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بسم اهلل الرحمن الرحيم
FACULTY OF ENGINEERING
ELECTRICAL ENGINEERING DEPARTMENT
ENEE520
WIRELESS QUEUING SYSTEM
Prepared by
Mousa Al-Shareef
Mohamad Lahaseh
Fadi Karajeh
Under the Guidance of
Mr Nofal Nofal
An Introduction to Graduation Project is submitted to the Electrical Engineering
Department in a partial Fulfillment of the Requirements for the Degree of BSc in
Electrical Engineering
BIRZIET
May - 2010
B
TABLE OF CONTENTS
Page
List of Tables I
List of Figures I
Abstract III
IV المستخلص
Chapter 1 Introduction to Wireless Queuing System 1
11 Queuing System 2
12 Why Wireless Queuing System 2
13
14
Basic Components of Queuing System
Basic Operation of Queuing System
3
3
15 Advantages of Queuing System 4
Chapter 2 Analysis and Performance of Queuing System
6
21 Introduction 7
22 What is the system 7
23
24
Types of Queuing System
Queuing System Characteristics
8
8
25 Birth Death Process 9
26 Queuing Behavior 11
27 System Statistics 11
28 Queuing System Modeling 14
C
29 Queuing System Notations 18
210 little‟s law 20
211 Server Utilization 21
212 Long-Run Measures of Performance 21
213 Steady State behavior of Infinite-Markovian Models 22
Chapter 3 Queuing System Components
25
31 Introduction 26
32 Entrance Numbering Unit 26
33 Teller Units 27
34 Display Units 28
35 Examples and Specifications of Some Practical Queuing
Systems
29
36 Connection of the System
34
Chapter 4 Wireless Technology
37
41 Introduction 38
42 WLANs Characteristics 39
43 Wi-Fi Technology 40
44
45
80211g Performance and Characteristics
Wi-Fi Access Protocol
41
44
46 Security Standards 44
47 Modulation
47
D
Conclusion and
Future Work
55
References
56
Appendix A
57
A1 MATLAB Code of PDF for Exponential Distribution 57
A2
A3
A4
A5
MATLAB Code of CDF for Exponential Distribution
MATLAB Code of PDF for Poisson Distribution
MATLAB Code of CDF for Poisson Distribution
Histogram of Average Waiting Time
57
57
58
58
A6 MATLAB Code to Calculate the Parameter of the
Queuing System From the Entered Lambda and Mu
59
E
List of Tables
I
Chapter 2
Chapter 4
2-1
2-2
2-3
2-4
2-5
4-1
4-2
Service Time Probability
Data Related to 20 Customers
Notations of Queuing System
Formulas for MG1
Formulas for MM1
Comparison between Wi-Fi Standards
Data Rates Parameters in 80211g
List of Figures
Chapter 1
1-1 Queuing System Configuration
Chapter 2
2-1
Flowchart for Departure Process
2-2
2-3
Flowchart for Arrival Process
Bank Queuing System
2-4
2-5
PDF for Poisson Distributions
CDF for Poisson Distributions
2-6 PDF for Exponential Distributions
2-7 CDF for Exponential Distributions
Chapter 3
3-1
Token Dispenser Unit
II
3-2 Terminal Unit
3-3 Main Display Unit
3-4
3-5
3-6
3-7
3-8
3-9
3-10
Counter Display Unit
TRONIX Wireless Queuing System
Automatic Queue Management System (AKIS)
LONBON Wireless Queuing Machine
Servicing the Customer
Practical System Connected Wirily
Practical System Connected Wirelessly
Chapter 4
4-1
Expected 80211a 80211b and 80211g Data Rates at
Varying Distance from Access Point
4-2 80211g Behavior in Different Environments
4-3 OFDM System Transmit Data on Multiple Subcarrier
4-4a Serial to Parallel Conversion
4-4b
4-5
4-6
4-7
4-8
4-9
4-10a
4-10b
OFDM Spectrum
Equivalent generation of OFDM signal
16-QAM constellation diagram
OFDM output with QAM incorporate
80211g OFDM carrier assignments
Simple OFDM Transmitter
OFDM Transmitter
OFDM Receiver
Abstract
III
Queuing systems are one of the most successful organizing techniques which are
used almost in every public place such as hospitals libraries sport centers museums
banks shopping centers and governmental institutions in order to spare peoples time and
effort by controlling and arranging their entrance waiting and servicing In this project
we will introduce all theoretical information and data needed to build a wireless queuing
system
The operation of such systems depend on the teller devices that will transmit
information to display units or LCDs through wireless channels also a server that saves
the readings and calculate every parameter that serves the customer such as number of
customers in the system or the queue waiting time service time and average time spent
in the system
The first part of this project focuses on studying the characteristics of queuing
systems and describing various models that implements them which contributes
significantly to improve the service quality in a customer oriented establishment
Furthermore statistical analysis can be adopted to achieve our goal such as Poisson-
Distribution Exponential Distribution and some measures of random variables
The second part deals with hardware devices which will generally be used to
construct the overall wireless queuing system These parts mainly consist of the Entrance
Numbering Unit the Teller Units and the Display Units A brief research on cost
availability and quality of components is taken into consideration Wireless techniques
are also introduced in order to be able to connect our system wirelessly for moving
purposes
MATLAB language program is used to illustrate some of the above operational and
statistical analysis
المستخلص
IV
ف اذس أ اصف أحذ أوثش ذماخ ارظ ااخحح اسرؼح ذمشثا ف ؼظ األاو االرظاسظا
ح اؼا ج شاوض اشاظح اراحف اثن شاوض ث اسرشفاخ اىرثاخ اؼا ساخ ق اؤطارس
ج ره ى ذفاحى خذر رظاساذشذة دخ اط الد ادذ ػ طشك س ػى ا
ف صف ارظاسظا اءةا حراج ار جي اؼاخ اثااخ اظشين لذط اششعف زا ح
السى
احذاخ ػشضحذاخ اي إى ؼاخ ذشس ار اإلخثاس أداخ ػى األظح ز ث ػ ػرذي
حسةي امشاءاخ فش ازي خاداي أعا االسى لاخ خالي ػذد ث اضت جخذي ا حراخ و
اظا ف اسره لدرسط اي خذحاي لد رظاساال ص اطاتس أ اظا ف اضتائ
طثمح ارج صف صفاي ظا ف الرظاسا خصائص دساسح ػى اششع زا األي ادضء شوض
صتؤسساخ ار ذخ اي اخذح ػح ذحس ف حظ تشى ذسا ز األظح خرفح
تؼط أس ذصغ تض ذصغ ث ذفا إحصائ ذح سم تؼ ره إى تاإلظافح
اؼشائ ارغش ػاخ
صفاي ف رظاساال ظا ثاء سرؼسد ياد األخضج داخاأل غ اششع اثا ادضء رؼا
ع لصش تحث اؼشض حذاخ خثاساإل حذاخ اذخ حذج اؼذ ػى ذش األخضاء ز االسى
اخ ػح ارافش اىفح ى أعا ذمذسف السىاي ذماخ االػرثاس تؼ ذؤخز سف اى
السى يتشه ظاا إصاي ػىساػذا خ
سسرخذ ف زا اششع تشاح ااذالب رحمك افا اظشح اإلحصائح
1
Chapter 1
Introduction to Wireless Queuing System
2
11 Queuing System
Queues build up in the institutes and companies that cater to large number of customers
where the customer service is necessary and the arrival rate to queue is larger than the service
rate Long time of waiting is unpleasant to customer and his service and therefore long queues
damage the company‟s image
Queuing System contributes significantly to improve the service quality in any customer
ndashoriented company Queuing System is ideal for bank university counter hospital and payment
center Queuing System avoid the dissatisfaction customer simply take a site where waiting his
turn to be served or reading advertisements
12 Why Wireless Queuing System
In this project we will build a practical Wireless Queuing System the use of the wireless
in the transfer of data is one of the major purposes of this project
Wireless network is commonly associated with a telecommunications network whose
interconnections between two nodes is implemented without using wires otherwise it is
implemented via some type of remote information transmission system that uses the EM waves
Such as radio wave
Our selections of the wireless refers to the features of this method of transfer data the
advantages using wireless rather than use another method are listed below
A) The addition of additional wires or drilling a new hole in office could be prohibited
impractical or too expensive
B) Flexibility of locations and data port required
C) Keep the look of the company nice
3
13 Basic Components of Queuing System
Queuing System consists from Server (PC) Entrance Numbering Unit Teller Unit
Display unit or Main LCD and other small LCDs
The components of Queuing System will discussed in chapter 3 but in this chapter let us
understand the basic operation of such a system
14 Basic Operations of Queuing System
There are two processes that affect the queuing system (birth process death process) To
explain the operation of the Queuing system we have to take each process independently and
show how the state of the system changes
To have a clear understanding of the operation of the Queuing System Let us assume that
it is installed in bank
When a customer enter the bank (birth occur) he will press on some key on the
numbering unit board or in some cases touch a sensitive screen then the Numbering unit
transfer the data to the server which make a calculations depend on two things first the number
of teller and customer in wait also on the profile and statistical data provided by the
programmer Then the server send information to the numbering unit contain the number of the
customer and the expected waiting time then it will print these information on a ticket also at
the same time the server communicates with Tellers units and Main LCD
However when a customer is served teller unit transfer data to the server which is
transfer these data to the main LCD so as a result a new customer is forwarding to the teller unit
The Figure [1-1] shows a simple graph for the Wireless Queuing System
4
Figure [1-1] Queuing System Configuration
15 Advantages of Queuing System [1]
Even though Queuing Systems improve the service quality in the company there are
several advantage of the use of such a system which are listed below
A) Reduction the waiting and service time for customers
Since the use of Queuing System avoid the dissatisfaction the service personal will work
in free conditions and he will served the customers efficiently so as a result the reduction of the
service and waiting time is achieved
B) Forward the customer to other operator
The use of such a system make it possible to forward the customer to other teller when
the first one is busy
C) Possibility to give a priority for a certain customer (Gold Customers)
In addition the Queuing system gives the flexibility to give a priority to certain
customers such as VIP person
D) Company manager can get report including statistical data
5
Also as a company use the Queuing System the manger can get statistical data this data
including the number served waiting time service rate and employee work loadhellipetc
This data give the manager indications to increase or decrease the number of employee
change the scenario on which the employee served the customers and other things related to the
company
E) The main display unit can not only show the information to the Queuing System but
also it can use to show the date and time and other advertising
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
B
TABLE OF CONTENTS
Page
List of Tables I
List of Figures I
Abstract III
IV المستخلص
Chapter 1 Introduction to Wireless Queuing System 1
11 Queuing System 2
12 Why Wireless Queuing System 2
13
14
Basic Components of Queuing System
Basic Operation of Queuing System
3
3
15 Advantages of Queuing System 4
Chapter 2 Analysis and Performance of Queuing System
6
21 Introduction 7
22 What is the system 7
23
24
Types of Queuing System
Queuing System Characteristics
8
8
25 Birth Death Process 9
26 Queuing Behavior 11
27 System Statistics 11
28 Queuing System Modeling 14
C
29 Queuing System Notations 18
210 little‟s law 20
211 Server Utilization 21
212 Long-Run Measures of Performance 21
213 Steady State behavior of Infinite-Markovian Models 22
Chapter 3 Queuing System Components
25
31 Introduction 26
32 Entrance Numbering Unit 26
33 Teller Units 27
34 Display Units 28
35 Examples and Specifications of Some Practical Queuing
Systems
29
36 Connection of the System
34
Chapter 4 Wireless Technology
37
41 Introduction 38
42 WLANs Characteristics 39
43 Wi-Fi Technology 40
44
45
80211g Performance and Characteristics
Wi-Fi Access Protocol
41
44
46 Security Standards 44
47 Modulation
47
D
Conclusion and
Future Work
55
References
56
Appendix A
57
A1 MATLAB Code of PDF for Exponential Distribution 57
A2
A3
A4
A5
MATLAB Code of CDF for Exponential Distribution
MATLAB Code of PDF for Poisson Distribution
MATLAB Code of CDF for Poisson Distribution
Histogram of Average Waiting Time
57
57
58
58
A6 MATLAB Code to Calculate the Parameter of the
Queuing System From the Entered Lambda and Mu
59
E
List of Tables
I
Chapter 2
Chapter 4
2-1
2-2
2-3
2-4
2-5
4-1
4-2
Service Time Probability
Data Related to 20 Customers
Notations of Queuing System
Formulas for MG1
Formulas for MM1
Comparison between Wi-Fi Standards
Data Rates Parameters in 80211g
List of Figures
Chapter 1
1-1 Queuing System Configuration
Chapter 2
2-1
Flowchart for Departure Process
2-2
2-3
Flowchart for Arrival Process
Bank Queuing System
2-4
2-5
PDF for Poisson Distributions
CDF for Poisson Distributions
2-6 PDF for Exponential Distributions
2-7 CDF for Exponential Distributions
Chapter 3
3-1
Token Dispenser Unit
II
3-2 Terminal Unit
3-3 Main Display Unit
3-4
3-5
3-6
3-7
3-8
3-9
3-10
Counter Display Unit
TRONIX Wireless Queuing System
Automatic Queue Management System (AKIS)
LONBON Wireless Queuing Machine
Servicing the Customer
Practical System Connected Wirily
Practical System Connected Wirelessly
Chapter 4
4-1
Expected 80211a 80211b and 80211g Data Rates at
Varying Distance from Access Point
4-2 80211g Behavior in Different Environments
4-3 OFDM System Transmit Data on Multiple Subcarrier
4-4a Serial to Parallel Conversion
4-4b
4-5
4-6
4-7
4-8
4-9
4-10a
4-10b
OFDM Spectrum
Equivalent generation of OFDM signal
16-QAM constellation diagram
OFDM output with QAM incorporate
80211g OFDM carrier assignments
Simple OFDM Transmitter
OFDM Transmitter
OFDM Receiver
Abstract
III
Queuing systems are one of the most successful organizing techniques which are
used almost in every public place such as hospitals libraries sport centers museums
banks shopping centers and governmental institutions in order to spare peoples time and
effort by controlling and arranging their entrance waiting and servicing In this project
we will introduce all theoretical information and data needed to build a wireless queuing
system
The operation of such systems depend on the teller devices that will transmit
information to display units or LCDs through wireless channels also a server that saves
the readings and calculate every parameter that serves the customer such as number of
customers in the system or the queue waiting time service time and average time spent
in the system
The first part of this project focuses on studying the characteristics of queuing
systems and describing various models that implements them which contributes
significantly to improve the service quality in a customer oriented establishment
Furthermore statistical analysis can be adopted to achieve our goal such as Poisson-
Distribution Exponential Distribution and some measures of random variables
The second part deals with hardware devices which will generally be used to
construct the overall wireless queuing system These parts mainly consist of the Entrance
Numbering Unit the Teller Units and the Display Units A brief research on cost
availability and quality of components is taken into consideration Wireless techniques
are also introduced in order to be able to connect our system wirelessly for moving
purposes
MATLAB language program is used to illustrate some of the above operational and
statistical analysis
المستخلص
IV
ف اذس أ اصف أحذ أوثش ذماخ ارظ ااخحح اسرؼح ذمشثا ف ؼظ األاو االرظاسظا
ح اؼا ج شاوض اشاظح اراحف اثن شاوض ث اسرشفاخ اىرثاخ اؼا ساخ ق اؤطارس
ج ره ى ذفاحى خذر رظاساذشذة دخ اط الد ادذ ػ طشك س ػى ا
ف صف ارظاسظا اءةا حراج ار جي اؼاخ اثااخ اظشين لذط اششعف زا ح
السى
احذاخ ػشضحذاخ اي إى ؼاخ ذشس ار اإلخثاس أداخ ػى األظح ز ث ػ ػرذي
حسةي امشاءاخ فش ازي خاداي أعا االسى لاخ خالي ػذد ث اضت جخذي ا حراخ و
اظا ف اسره لدرسط اي خذحاي لد رظاساال ص اطاتس أ اظا ف اضتائ
طثمح ارج صف صفاي ظا ف الرظاسا خصائص دساسح ػى اششع زا األي ادضء شوض
صتؤسساخ ار ذخ اي اخذح ػح ذحس ف حظ تشى ذسا ز األظح خرفح
تؼط أس ذصغ تض ذصغ ث ذفا إحصائ ذح سم تؼ ره إى تاإلظافح
اؼشائ ارغش ػاخ
صفاي ف رظاساال ظا ثاء سرؼسد ياد األخضج داخاأل غ اششع اثا ادضء رؼا
ع لصش تحث اؼشض حذاخ خثاساإل حذاخ اذخ حذج اؼذ ػى ذش األخضاء ز االسى
اخ ػح ارافش اىفح ى أعا ذمذسف السىاي ذماخ االػرثاس تؼ ذؤخز سف اى
السى يتشه ظاا إصاي ػىساػذا خ
سسرخذ ف زا اششع تشاح ااذالب رحمك افا اظشح اإلحصائح
1
Chapter 1
Introduction to Wireless Queuing System
2
11 Queuing System
Queues build up in the institutes and companies that cater to large number of customers
where the customer service is necessary and the arrival rate to queue is larger than the service
rate Long time of waiting is unpleasant to customer and his service and therefore long queues
damage the company‟s image
Queuing System contributes significantly to improve the service quality in any customer
ndashoriented company Queuing System is ideal for bank university counter hospital and payment
center Queuing System avoid the dissatisfaction customer simply take a site where waiting his
turn to be served or reading advertisements
12 Why Wireless Queuing System
In this project we will build a practical Wireless Queuing System the use of the wireless
in the transfer of data is one of the major purposes of this project
Wireless network is commonly associated with a telecommunications network whose
interconnections between two nodes is implemented without using wires otherwise it is
implemented via some type of remote information transmission system that uses the EM waves
Such as radio wave
Our selections of the wireless refers to the features of this method of transfer data the
advantages using wireless rather than use another method are listed below
A) The addition of additional wires or drilling a new hole in office could be prohibited
impractical or too expensive
B) Flexibility of locations and data port required
C) Keep the look of the company nice
3
13 Basic Components of Queuing System
Queuing System consists from Server (PC) Entrance Numbering Unit Teller Unit
Display unit or Main LCD and other small LCDs
The components of Queuing System will discussed in chapter 3 but in this chapter let us
understand the basic operation of such a system
14 Basic Operations of Queuing System
There are two processes that affect the queuing system (birth process death process) To
explain the operation of the Queuing system we have to take each process independently and
show how the state of the system changes
To have a clear understanding of the operation of the Queuing System Let us assume that
it is installed in bank
When a customer enter the bank (birth occur) he will press on some key on the
numbering unit board or in some cases touch a sensitive screen then the Numbering unit
transfer the data to the server which make a calculations depend on two things first the number
of teller and customer in wait also on the profile and statistical data provided by the
programmer Then the server send information to the numbering unit contain the number of the
customer and the expected waiting time then it will print these information on a ticket also at
the same time the server communicates with Tellers units and Main LCD
However when a customer is served teller unit transfer data to the server which is
transfer these data to the main LCD so as a result a new customer is forwarding to the teller unit
The Figure [1-1] shows a simple graph for the Wireless Queuing System
4
Figure [1-1] Queuing System Configuration
15 Advantages of Queuing System [1]
Even though Queuing Systems improve the service quality in the company there are
several advantage of the use of such a system which are listed below
A) Reduction the waiting and service time for customers
Since the use of Queuing System avoid the dissatisfaction the service personal will work
in free conditions and he will served the customers efficiently so as a result the reduction of the
service and waiting time is achieved
B) Forward the customer to other operator
The use of such a system make it possible to forward the customer to other teller when
the first one is busy
C) Possibility to give a priority for a certain customer (Gold Customers)
In addition the Queuing system gives the flexibility to give a priority to certain
customers such as VIP person
D) Company manager can get report including statistical data
5
Also as a company use the Queuing System the manger can get statistical data this data
including the number served waiting time service rate and employee work loadhellipetc
This data give the manager indications to increase or decrease the number of employee
change the scenario on which the employee served the customers and other things related to the
company
E) The main display unit can not only show the information to the Queuing System but
also it can use to show the date and time and other advertising
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
C
29 Queuing System Notations 18
210 little‟s law 20
211 Server Utilization 21
212 Long-Run Measures of Performance 21
213 Steady State behavior of Infinite-Markovian Models 22
Chapter 3 Queuing System Components
25
31 Introduction 26
32 Entrance Numbering Unit 26
33 Teller Units 27
34 Display Units 28
35 Examples and Specifications of Some Practical Queuing
Systems
29
36 Connection of the System
34
Chapter 4 Wireless Technology
37
41 Introduction 38
42 WLANs Characteristics 39
43 Wi-Fi Technology 40
44
45
80211g Performance and Characteristics
Wi-Fi Access Protocol
41
44
46 Security Standards 44
47 Modulation
47
D
Conclusion and
Future Work
55
References
56
Appendix A
57
A1 MATLAB Code of PDF for Exponential Distribution 57
A2
A3
A4
A5
MATLAB Code of CDF for Exponential Distribution
MATLAB Code of PDF for Poisson Distribution
MATLAB Code of CDF for Poisson Distribution
Histogram of Average Waiting Time
57
57
58
58
A6 MATLAB Code to Calculate the Parameter of the
Queuing System From the Entered Lambda and Mu
59
E
List of Tables
I
Chapter 2
Chapter 4
2-1
2-2
2-3
2-4
2-5
4-1
4-2
Service Time Probability
Data Related to 20 Customers
Notations of Queuing System
Formulas for MG1
Formulas for MM1
Comparison between Wi-Fi Standards
Data Rates Parameters in 80211g
List of Figures
Chapter 1
1-1 Queuing System Configuration
Chapter 2
2-1
Flowchart for Departure Process
2-2
2-3
Flowchart for Arrival Process
Bank Queuing System
2-4
2-5
PDF for Poisson Distributions
CDF for Poisson Distributions
2-6 PDF for Exponential Distributions
2-7 CDF for Exponential Distributions
Chapter 3
3-1
Token Dispenser Unit
II
3-2 Terminal Unit
3-3 Main Display Unit
3-4
3-5
3-6
3-7
3-8
3-9
3-10
Counter Display Unit
TRONIX Wireless Queuing System
Automatic Queue Management System (AKIS)
LONBON Wireless Queuing Machine
Servicing the Customer
Practical System Connected Wirily
Practical System Connected Wirelessly
Chapter 4
4-1
Expected 80211a 80211b and 80211g Data Rates at
Varying Distance from Access Point
4-2 80211g Behavior in Different Environments
4-3 OFDM System Transmit Data on Multiple Subcarrier
4-4a Serial to Parallel Conversion
4-4b
4-5
4-6
4-7
4-8
4-9
4-10a
4-10b
OFDM Spectrum
Equivalent generation of OFDM signal
16-QAM constellation diagram
OFDM output with QAM incorporate
80211g OFDM carrier assignments
Simple OFDM Transmitter
OFDM Transmitter
OFDM Receiver
Abstract
III
Queuing systems are one of the most successful organizing techniques which are
used almost in every public place such as hospitals libraries sport centers museums
banks shopping centers and governmental institutions in order to spare peoples time and
effort by controlling and arranging their entrance waiting and servicing In this project
we will introduce all theoretical information and data needed to build a wireless queuing
system
The operation of such systems depend on the teller devices that will transmit
information to display units or LCDs through wireless channels also a server that saves
the readings and calculate every parameter that serves the customer such as number of
customers in the system or the queue waiting time service time and average time spent
in the system
The first part of this project focuses on studying the characteristics of queuing
systems and describing various models that implements them which contributes
significantly to improve the service quality in a customer oriented establishment
Furthermore statistical analysis can be adopted to achieve our goal such as Poisson-
Distribution Exponential Distribution and some measures of random variables
The second part deals with hardware devices which will generally be used to
construct the overall wireless queuing system These parts mainly consist of the Entrance
Numbering Unit the Teller Units and the Display Units A brief research on cost
availability and quality of components is taken into consideration Wireless techniques
are also introduced in order to be able to connect our system wirelessly for moving
purposes
MATLAB language program is used to illustrate some of the above operational and
statistical analysis
المستخلص
IV
ف اذس أ اصف أحذ أوثش ذماخ ارظ ااخحح اسرؼح ذمشثا ف ؼظ األاو االرظاسظا
ح اؼا ج شاوض اشاظح اراحف اثن شاوض ث اسرشفاخ اىرثاخ اؼا ساخ ق اؤطارس
ج ره ى ذفاحى خذر رظاساذشذة دخ اط الد ادذ ػ طشك س ػى ا
ف صف ارظاسظا اءةا حراج ار جي اؼاخ اثااخ اظشين لذط اششعف زا ح
السى
احذاخ ػشضحذاخ اي إى ؼاخ ذشس ار اإلخثاس أداخ ػى األظح ز ث ػ ػرذي
حسةي امشاءاخ فش ازي خاداي أعا االسى لاخ خالي ػذد ث اضت جخذي ا حراخ و
اظا ف اسره لدرسط اي خذحاي لد رظاساال ص اطاتس أ اظا ف اضتائ
طثمح ارج صف صفاي ظا ف الرظاسا خصائص دساسح ػى اششع زا األي ادضء شوض
صتؤسساخ ار ذخ اي اخذح ػح ذحس ف حظ تشى ذسا ز األظح خرفح
تؼط أس ذصغ تض ذصغ ث ذفا إحصائ ذح سم تؼ ره إى تاإلظافح
اؼشائ ارغش ػاخ
صفاي ف رظاساال ظا ثاء سرؼسد ياد األخضج داخاأل غ اششع اثا ادضء رؼا
ع لصش تحث اؼشض حذاخ خثاساإل حذاخ اذخ حذج اؼذ ػى ذش األخضاء ز االسى
اخ ػح ارافش اىفح ى أعا ذمذسف السىاي ذماخ االػرثاس تؼ ذؤخز سف اى
السى يتشه ظاا إصاي ػىساػذا خ
سسرخذ ف زا اششع تشاح ااذالب رحمك افا اظشح اإلحصائح
1
Chapter 1
Introduction to Wireless Queuing System
2
11 Queuing System
Queues build up in the institutes and companies that cater to large number of customers
where the customer service is necessary and the arrival rate to queue is larger than the service
rate Long time of waiting is unpleasant to customer and his service and therefore long queues
damage the company‟s image
Queuing System contributes significantly to improve the service quality in any customer
ndashoriented company Queuing System is ideal for bank university counter hospital and payment
center Queuing System avoid the dissatisfaction customer simply take a site where waiting his
turn to be served or reading advertisements
12 Why Wireless Queuing System
In this project we will build a practical Wireless Queuing System the use of the wireless
in the transfer of data is one of the major purposes of this project
Wireless network is commonly associated with a telecommunications network whose
interconnections between two nodes is implemented without using wires otherwise it is
implemented via some type of remote information transmission system that uses the EM waves
Such as radio wave
Our selections of the wireless refers to the features of this method of transfer data the
advantages using wireless rather than use another method are listed below
A) The addition of additional wires or drilling a new hole in office could be prohibited
impractical or too expensive
B) Flexibility of locations and data port required
C) Keep the look of the company nice
3
13 Basic Components of Queuing System
Queuing System consists from Server (PC) Entrance Numbering Unit Teller Unit
Display unit or Main LCD and other small LCDs
The components of Queuing System will discussed in chapter 3 but in this chapter let us
understand the basic operation of such a system
14 Basic Operations of Queuing System
There are two processes that affect the queuing system (birth process death process) To
explain the operation of the Queuing system we have to take each process independently and
show how the state of the system changes
To have a clear understanding of the operation of the Queuing System Let us assume that
it is installed in bank
When a customer enter the bank (birth occur) he will press on some key on the
numbering unit board or in some cases touch a sensitive screen then the Numbering unit
transfer the data to the server which make a calculations depend on two things first the number
of teller and customer in wait also on the profile and statistical data provided by the
programmer Then the server send information to the numbering unit contain the number of the
customer and the expected waiting time then it will print these information on a ticket also at
the same time the server communicates with Tellers units and Main LCD
However when a customer is served teller unit transfer data to the server which is
transfer these data to the main LCD so as a result a new customer is forwarding to the teller unit
The Figure [1-1] shows a simple graph for the Wireless Queuing System
4
Figure [1-1] Queuing System Configuration
15 Advantages of Queuing System [1]
Even though Queuing Systems improve the service quality in the company there are
several advantage of the use of such a system which are listed below
A) Reduction the waiting and service time for customers
Since the use of Queuing System avoid the dissatisfaction the service personal will work
in free conditions and he will served the customers efficiently so as a result the reduction of the
service and waiting time is achieved
B) Forward the customer to other operator
The use of such a system make it possible to forward the customer to other teller when
the first one is busy
C) Possibility to give a priority for a certain customer (Gold Customers)
In addition the Queuing system gives the flexibility to give a priority to certain
customers such as VIP person
D) Company manager can get report including statistical data
5
Also as a company use the Queuing System the manger can get statistical data this data
including the number served waiting time service rate and employee work loadhellipetc
This data give the manager indications to increase or decrease the number of employee
change the scenario on which the employee served the customers and other things related to the
company
E) The main display unit can not only show the information to the Queuing System but
also it can use to show the date and time and other advertising
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
D
Conclusion and
Future Work
55
References
56
Appendix A
57
A1 MATLAB Code of PDF for Exponential Distribution 57
A2
A3
A4
A5
MATLAB Code of CDF for Exponential Distribution
MATLAB Code of PDF for Poisson Distribution
MATLAB Code of CDF for Poisson Distribution
Histogram of Average Waiting Time
57
57
58
58
A6 MATLAB Code to Calculate the Parameter of the
Queuing System From the Entered Lambda and Mu
59
E
List of Tables
I
Chapter 2
Chapter 4
2-1
2-2
2-3
2-4
2-5
4-1
4-2
Service Time Probability
Data Related to 20 Customers
Notations of Queuing System
Formulas for MG1
Formulas for MM1
Comparison between Wi-Fi Standards
Data Rates Parameters in 80211g
List of Figures
Chapter 1
1-1 Queuing System Configuration
Chapter 2
2-1
Flowchart for Departure Process
2-2
2-3
Flowchart for Arrival Process
Bank Queuing System
2-4
2-5
PDF for Poisson Distributions
CDF for Poisson Distributions
2-6 PDF for Exponential Distributions
2-7 CDF for Exponential Distributions
Chapter 3
3-1
Token Dispenser Unit
II
3-2 Terminal Unit
3-3 Main Display Unit
3-4
3-5
3-6
3-7
3-8
3-9
3-10
Counter Display Unit
TRONIX Wireless Queuing System
Automatic Queue Management System (AKIS)
LONBON Wireless Queuing Machine
Servicing the Customer
Practical System Connected Wirily
Practical System Connected Wirelessly
Chapter 4
4-1
Expected 80211a 80211b and 80211g Data Rates at
Varying Distance from Access Point
4-2 80211g Behavior in Different Environments
4-3 OFDM System Transmit Data on Multiple Subcarrier
4-4a Serial to Parallel Conversion
4-4b
4-5
4-6
4-7
4-8
4-9
4-10a
4-10b
OFDM Spectrum
Equivalent generation of OFDM signal
16-QAM constellation diagram
OFDM output with QAM incorporate
80211g OFDM carrier assignments
Simple OFDM Transmitter
OFDM Transmitter
OFDM Receiver
Abstract
III
Queuing systems are one of the most successful organizing techniques which are
used almost in every public place such as hospitals libraries sport centers museums
banks shopping centers and governmental institutions in order to spare peoples time and
effort by controlling and arranging their entrance waiting and servicing In this project
we will introduce all theoretical information and data needed to build a wireless queuing
system
The operation of such systems depend on the teller devices that will transmit
information to display units or LCDs through wireless channels also a server that saves
the readings and calculate every parameter that serves the customer such as number of
customers in the system or the queue waiting time service time and average time spent
in the system
The first part of this project focuses on studying the characteristics of queuing
systems and describing various models that implements them which contributes
significantly to improve the service quality in a customer oriented establishment
Furthermore statistical analysis can be adopted to achieve our goal such as Poisson-
Distribution Exponential Distribution and some measures of random variables
The second part deals with hardware devices which will generally be used to
construct the overall wireless queuing system These parts mainly consist of the Entrance
Numbering Unit the Teller Units and the Display Units A brief research on cost
availability and quality of components is taken into consideration Wireless techniques
are also introduced in order to be able to connect our system wirelessly for moving
purposes
MATLAB language program is used to illustrate some of the above operational and
statistical analysis
المستخلص
IV
ف اذس أ اصف أحذ أوثش ذماخ ارظ ااخحح اسرؼح ذمشثا ف ؼظ األاو االرظاسظا
ح اؼا ج شاوض اشاظح اراحف اثن شاوض ث اسرشفاخ اىرثاخ اؼا ساخ ق اؤطارس
ج ره ى ذفاحى خذر رظاساذشذة دخ اط الد ادذ ػ طشك س ػى ا
ف صف ارظاسظا اءةا حراج ار جي اؼاخ اثااخ اظشين لذط اششعف زا ح
السى
احذاخ ػشضحذاخ اي إى ؼاخ ذشس ار اإلخثاس أداخ ػى األظح ز ث ػ ػرذي
حسةي امشاءاخ فش ازي خاداي أعا االسى لاخ خالي ػذد ث اضت جخذي ا حراخ و
اظا ف اسره لدرسط اي خذحاي لد رظاساال ص اطاتس أ اظا ف اضتائ
طثمح ارج صف صفاي ظا ف الرظاسا خصائص دساسح ػى اششع زا األي ادضء شوض
صتؤسساخ ار ذخ اي اخذح ػح ذحس ف حظ تشى ذسا ز األظح خرفح
تؼط أس ذصغ تض ذصغ ث ذفا إحصائ ذح سم تؼ ره إى تاإلظافح
اؼشائ ارغش ػاخ
صفاي ف رظاساال ظا ثاء سرؼسد ياد األخضج داخاأل غ اششع اثا ادضء رؼا
ع لصش تحث اؼشض حذاخ خثاساإل حذاخ اذخ حذج اؼذ ػى ذش األخضاء ز االسى
اخ ػح ارافش اىفح ى أعا ذمذسف السىاي ذماخ االػرثاس تؼ ذؤخز سف اى
السى يتشه ظاا إصاي ػىساػذا خ
سسرخذ ف زا اششع تشاح ااذالب رحمك افا اظشح اإلحصائح
1
Chapter 1
Introduction to Wireless Queuing System
2
11 Queuing System
Queues build up in the institutes and companies that cater to large number of customers
where the customer service is necessary and the arrival rate to queue is larger than the service
rate Long time of waiting is unpleasant to customer and his service and therefore long queues
damage the company‟s image
Queuing System contributes significantly to improve the service quality in any customer
ndashoriented company Queuing System is ideal for bank university counter hospital and payment
center Queuing System avoid the dissatisfaction customer simply take a site where waiting his
turn to be served or reading advertisements
12 Why Wireless Queuing System
In this project we will build a practical Wireless Queuing System the use of the wireless
in the transfer of data is one of the major purposes of this project
Wireless network is commonly associated with a telecommunications network whose
interconnections between two nodes is implemented without using wires otherwise it is
implemented via some type of remote information transmission system that uses the EM waves
Such as radio wave
Our selections of the wireless refers to the features of this method of transfer data the
advantages using wireless rather than use another method are listed below
A) The addition of additional wires or drilling a new hole in office could be prohibited
impractical or too expensive
B) Flexibility of locations and data port required
C) Keep the look of the company nice
3
13 Basic Components of Queuing System
Queuing System consists from Server (PC) Entrance Numbering Unit Teller Unit
Display unit or Main LCD and other small LCDs
The components of Queuing System will discussed in chapter 3 but in this chapter let us
understand the basic operation of such a system
14 Basic Operations of Queuing System
There are two processes that affect the queuing system (birth process death process) To
explain the operation of the Queuing system we have to take each process independently and
show how the state of the system changes
To have a clear understanding of the operation of the Queuing System Let us assume that
it is installed in bank
When a customer enter the bank (birth occur) he will press on some key on the
numbering unit board or in some cases touch a sensitive screen then the Numbering unit
transfer the data to the server which make a calculations depend on two things first the number
of teller and customer in wait also on the profile and statistical data provided by the
programmer Then the server send information to the numbering unit contain the number of the
customer and the expected waiting time then it will print these information on a ticket also at
the same time the server communicates with Tellers units and Main LCD
However when a customer is served teller unit transfer data to the server which is
transfer these data to the main LCD so as a result a new customer is forwarding to the teller unit
The Figure [1-1] shows a simple graph for the Wireless Queuing System
4
Figure [1-1] Queuing System Configuration
15 Advantages of Queuing System [1]
Even though Queuing Systems improve the service quality in the company there are
several advantage of the use of such a system which are listed below
A) Reduction the waiting and service time for customers
Since the use of Queuing System avoid the dissatisfaction the service personal will work
in free conditions and he will served the customers efficiently so as a result the reduction of the
service and waiting time is achieved
B) Forward the customer to other operator
The use of such a system make it possible to forward the customer to other teller when
the first one is busy
C) Possibility to give a priority for a certain customer (Gold Customers)
In addition the Queuing system gives the flexibility to give a priority to certain
customers such as VIP person
D) Company manager can get report including statistical data
5
Also as a company use the Queuing System the manger can get statistical data this data
including the number served waiting time service rate and employee work loadhellipetc
This data give the manager indications to increase or decrease the number of employee
change the scenario on which the employee served the customers and other things related to the
company
E) The main display unit can not only show the information to the Queuing System but
also it can use to show the date and time and other advertising
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
E
List of Tables
I
Chapter 2
Chapter 4
2-1
2-2
2-3
2-4
2-5
4-1
4-2
Service Time Probability
Data Related to 20 Customers
Notations of Queuing System
Formulas for MG1
Formulas for MM1
Comparison between Wi-Fi Standards
Data Rates Parameters in 80211g
List of Figures
Chapter 1
1-1 Queuing System Configuration
Chapter 2
2-1
Flowchart for Departure Process
2-2
2-3
Flowchart for Arrival Process
Bank Queuing System
2-4
2-5
PDF for Poisson Distributions
CDF for Poisson Distributions
2-6 PDF for Exponential Distributions
2-7 CDF for Exponential Distributions
Chapter 3
3-1
Token Dispenser Unit
II
3-2 Terminal Unit
3-3 Main Display Unit
3-4
3-5
3-6
3-7
3-8
3-9
3-10
Counter Display Unit
TRONIX Wireless Queuing System
Automatic Queue Management System (AKIS)
LONBON Wireless Queuing Machine
Servicing the Customer
Practical System Connected Wirily
Practical System Connected Wirelessly
Chapter 4
4-1
Expected 80211a 80211b and 80211g Data Rates at
Varying Distance from Access Point
4-2 80211g Behavior in Different Environments
4-3 OFDM System Transmit Data on Multiple Subcarrier
4-4a Serial to Parallel Conversion
4-4b
4-5
4-6
4-7
4-8
4-9
4-10a
4-10b
OFDM Spectrum
Equivalent generation of OFDM signal
16-QAM constellation diagram
OFDM output with QAM incorporate
80211g OFDM carrier assignments
Simple OFDM Transmitter
OFDM Transmitter
OFDM Receiver
Abstract
III
Queuing systems are one of the most successful organizing techniques which are
used almost in every public place such as hospitals libraries sport centers museums
banks shopping centers and governmental institutions in order to spare peoples time and
effort by controlling and arranging their entrance waiting and servicing In this project
we will introduce all theoretical information and data needed to build a wireless queuing
system
The operation of such systems depend on the teller devices that will transmit
information to display units or LCDs through wireless channels also a server that saves
the readings and calculate every parameter that serves the customer such as number of
customers in the system or the queue waiting time service time and average time spent
in the system
The first part of this project focuses on studying the characteristics of queuing
systems and describing various models that implements them which contributes
significantly to improve the service quality in a customer oriented establishment
Furthermore statistical analysis can be adopted to achieve our goal such as Poisson-
Distribution Exponential Distribution and some measures of random variables
The second part deals with hardware devices which will generally be used to
construct the overall wireless queuing system These parts mainly consist of the Entrance
Numbering Unit the Teller Units and the Display Units A brief research on cost
availability and quality of components is taken into consideration Wireless techniques
are also introduced in order to be able to connect our system wirelessly for moving
purposes
MATLAB language program is used to illustrate some of the above operational and
statistical analysis
المستخلص
IV
ف اذس أ اصف أحذ أوثش ذماخ ارظ ااخحح اسرؼح ذمشثا ف ؼظ األاو االرظاسظا
ح اؼا ج شاوض اشاظح اراحف اثن شاوض ث اسرشفاخ اىرثاخ اؼا ساخ ق اؤطارس
ج ره ى ذفاحى خذر رظاساذشذة دخ اط الد ادذ ػ طشك س ػى ا
ف صف ارظاسظا اءةا حراج ار جي اؼاخ اثااخ اظشين لذط اششعف زا ح
السى
احذاخ ػشضحذاخ اي إى ؼاخ ذشس ار اإلخثاس أداخ ػى األظح ز ث ػ ػرذي
حسةي امشاءاخ فش ازي خاداي أعا االسى لاخ خالي ػذد ث اضت جخذي ا حراخ و
اظا ف اسره لدرسط اي خذحاي لد رظاساال ص اطاتس أ اظا ف اضتائ
طثمح ارج صف صفاي ظا ف الرظاسا خصائص دساسح ػى اششع زا األي ادضء شوض
صتؤسساخ ار ذخ اي اخذح ػح ذحس ف حظ تشى ذسا ز األظح خرفح
تؼط أس ذصغ تض ذصغ ث ذفا إحصائ ذح سم تؼ ره إى تاإلظافح
اؼشائ ارغش ػاخ
صفاي ف رظاساال ظا ثاء سرؼسد ياد األخضج داخاأل غ اششع اثا ادضء رؼا
ع لصش تحث اؼشض حذاخ خثاساإل حذاخ اذخ حذج اؼذ ػى ذش األخضاء ز االسى
اخ ػح ارافش اىفح ى أعا ذمذسف السىاي ذماخ االػرثاس تؼ ذؤخز سف اى
السى يتشه ظاا إصاي ػىساػذا خ
سسرخذ ف زا اششع تشاح ااذالب رحمك افا اظشح اإلحصائح
1
Chapter 1
Introduction to Wireless Queuing System
2
11 Queuing System
Queues build up in the institutes and companies that cater to large number of customers
where the customer service is necessary and the arrival rate to queue is larger than the service
rate Long time of waiting is unpleasant to customer and his service and therefore long queues
damage the company‟s image
Queuing System contributes significantly to improve the service quality in any customer
ndashoriented company Queuing System is ideal for bank university counter hospital and payment
center Queuing System avoid the dissatisfaction customer simply take a site where waiting his
turn to be served or reading advertisements
12 Why Wireless Queuing System
In this project we will build a practical Wireless Queuing System the use of the wireless
in the transfer of data is one of the major purposes of this project
Wireless network is commonly associated with a telecommunications network whose
interconnections between two nodes is implemented without using wires otherwise it is
implemented via some type of remote information transmission system that uses the EM waves
Such as radio wave
Our selections of the wireless refers to the features of this method of transfer data the
advantages using wireless rather than use another method are listed below
A) The addition of additional wires or drilling a new hole in office could be prohibited
impractical or too expensive
B) Flexibility of locations and data port required
C) Keep the look of the company nice
3
13 Basic Components of Queuing System
Queuing System consists from Server (PC) Entrance Numbering Unit Teller Unit
Display unit or Main LCD and other small LCDs
The components of Queuing System will discussed in chapter 3 but in this chapter let us
understand the basic operation of such a system
14 Basic Operations of Queuing System
There are two processes that affect the queuing system (birth process death process) To
explain the operation of the Queuing system we have to take each process independently and
show how the state of the system changes
To have a clear understanding of the operation of the Queuing System Let us assume that
it is installed in bank
When a customer enter the bank (birth occur) he will press on some key on the
numbering unit board or in some cases touch a sensitive screen then the Numbering unit
transfer the data to the server which make a calculations depend on two things first the number
of teller and customer in wait also on the profile and statistical data provided by the
programmer Then the server send information to the numbering unit contain the number of the
customer and the expected waiting time then it will print these information on a ticket also at
the same time the server communicates with Tellers units and Main LCD
However when a customer is served teller unit transfer data to the server which is
transfer these data to the main LCD so as a result a new customer is forwarding to the teller unit
The Figure [1-1] shows a simple graph for the Wireless Queuing System
4
Figure [1-1] Queuing System Configuration
15 Advantages of Queuing System [1]
Even though Queuing Systems improve the service quality in the company there are
several advantage of the use of such a system which are listed below
A) Reduction the waiting and service time for customers
Since the use of Queuing System avoid the dissatisfaction the service personal will work
in free conditions and he will served the customers efficiently so as a result the reduction of the
service and waiting time is achieved
B) Forward the customer to other operator
The use of such a system make it possible to forward the customer to other teller when
the first one is busy
C) Possibility to give a priority for a certain customer (Gold Customers)
In addition the Queuing system gives the flexibility to give a priority to certain
customers such as VIP person
D) Company manager can get report including statistical data
5
Also as a company use the Queuing System the manger can get statistical data this data
including the number served waiting time service rate and employee work loadhellipetc
This data give the manager indications to increase or decrease the number of employee
change the scenario on which the employee served the customers and other things related to the
company
E) The main display unit can not only show the information to the Queuing System but
also it can use to show the date and time and other advertising
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
I
Chapter 2
Chapter 4
2-1
2-2
2-3
2-4
2-5
4-1
4-2
Service Time Probability
Data Related to 20 Customers
Notations of Queuing System
Formulas for MG1
Formulas for MM1
Comparison between Wi-Fi Standards
Data Rates Parameters in 80211g
List of Figures
Chapter 1
1-1 Queuing System Configuration
Chapter 2
2-1
Flowchart for Departure Process
2-2
2-3
Flowchart for Arrival Process
Bank Queuing System
2-4
2-5
PDF for Poisson Distributions
CDF for Poisson Distributions
2-6 PDF for Exponential Distributions
2-7 CDF for Exponential Distributions
Chapter 3
3-1
Token Dispenser Unit
II
3-2 Terminal Unit
3-3 Main Display Unit
3-4
3-5
3-6
3-7
3-8
3-9
3-10
Counter Display Unit
TRONIX Wireless Queuing System
Automatic Queue Management System (AKIS)
LONBON Wireless Queuing Machine
Servicing the Customer
Practical System Connected Wirily
Practical System Connected Wirelessly
Chapter 4
4-1
Expected 80211a 80211b and 80211g Data Rates at
Varying Distance from Access Point
4-2 80211g Behavior in Different Environments
4-3 OFDM System Transmit Data on Multiple Subcarrier
4-4a Serial to Parallel Conversion
4-4b
4-5
4-6
4-7
4-8
4-9
4-10a
4-10b
OFDM Spectrum
Equivalent generation of OFDM signal
16-QAM constellation diagram
OFDM output with QAM incorporate
80211g OFDM carrier assignments
Simple OFDM Transmitter
OFDM Transmitter
OFDM Receiver
Abstract
III
Queuing systems are one of the most successful organizing techniques which are
used almost in every public place such as hospitals libraries sport centers museums
banks shopping centers and governmental institutions in order to spare peoples time and
effort by controlling and arranging their entrance waiting and servicing In this project
we will introduce all theoretical information and data needed to build a wireless queuing
system
The operation of such systems depend on the teller devices that will transmit
information to display units or LCDs through wireless channels also a server that saves
the readings and calculate every parameter that serves the customer such as number of
customers in the system or the queue waiting time service time and average time spent
in the system
The first part of this project focuses on studying the characteristics of queuing
systems and describing various models that implements them which contributes
significantly to improve the service quality in a customer oriented establishment
Furthermore statistical analysis can be adopted to achieve our goal such as Poisson-
Distribution Exponential Distribution and some measures of random variables
The second part deals with hardware devices which will generally be used to
construct the overall wireless queuing system These parts mainly consist of the Entrance
Numbering Unit the Teller Units and the Display Units A brief research on cost
availability and quality of components is taken into consideration Wireless techniques
are also introduced in order to be able to connect our system wirelessly for moving
purposes
MATLAB language program is used to illustrate some of the above operational and
statistical analysis
المستخلص
IV
ف اذس أ اصف أحذ أوثش ذماخ ارظ ااخحح اسرؼح ذمشثا ف ؼظ األاو االرظاسظا
ح اؼا ج شاوض اشاظح اراحف اثن شاوض ث اسرشفاخ اىرثاخ اؼا ساخ ق اؤطارس
ج ره ى ذفاحى خذر رظاساذشذة دخ اط الد ادذ ػ طشك س ػى ا
ف صف ارظاسظا اءةا حراج ار جي اؼاخ اثااخ اظشين لذط اششعف زا ح
السى
احذاخ ػشضحذاخ اي إى ؼاخ ذشس ار اإلخثاس أداخ ػى األظح ز ث ػ ػرذي
حسةي امشاءاخ فش ازي خاداي أعا االسى لاخ خالي ػذد ث اضت جخذي ا حراخ و
اظا ف اسره لدرسط اي خذحاي لد رظاساال ص اطاتس أ اظا ف اضتائ
طثمح ارج صف صفاي ظا ف الرظاسا خصائص دساسح ػى اششع زا األي ادضء شوض
صتؤسساخ ار ذخ اي اخذح ػح ذحس ف حظ تشى ذسا ز األظح خرفح
تؼط أس ذصغ تض ذصغ ث ذفا إحصائ ذح سم تؼ ره إى تاإلظافح
اؼشائ ارغش ػاخ
صفاي ف رظاساال ظا ثاء سرؼسد ياد األخضج داخاأل غ اششع اثا ادضء رؼا
ع لصش تحث اؼشض حذاخ خثاساإل حذاخ اذخ حذج اؼذ ػى ذش األخضاء ز االسى
اخ ػح ارافش اىفح ى أعا ذمذسف السىاي ذماخ االػرثاس تؼ ذؤخز سف اى
السى يتشه ظاا إصاي ػىساػذا خ
سسرخذ ف زا اششع تشاح ااذالب رحمك افا اظشح اإلحصائح
1
Chapter 1
Introduction to Wireless Queuing System
2
11 Queuing System
Queues build up in the institutes and companies that cater to large number of customers
where the customer service is necessary and the arrival rate to queue is larger than the service
rate Long time of waiting is unpleasant to customer and his service and therefore long queues
damage the company‟s image
Queuing System contributes significantly to improve the service quality in any customer
ndashoriented company Queuing System is ideal for bank university counter hospital and payment
center Queuing System avoid the dissatisfaction customer simply take a site where waiting his
turn to be served or reading advertisements
12 Why Wireless Queuing System
In this project we will build a practical Wireless Queuing System the use of the wireless
in the transfer of data is one of the major purposes of this project
Wireless network is commonly associated with a telecommunications network whose
interconnections between two nodes is implemented without using wires otherwise it is
implemented via some type of remote information transmission system that uses the EM waves
Such as radio wave
Our selections of the wireless refers to the features of this method of transfer data the
advantages using wireless rather than use another method are listed below
A) The addition of additional wires or drilling a new hole in office could be prohibited
impractical or too expensive
B) Flexibility of locations and data port required
C) Keep the look of the company nice
3
13 Basic Components of Queuing System
Queuing System consists from Server (PC) Entrance Numbering Unit Teller Unit
Display unit or Main LCD and other small LCDs
The components of Queuing System will discussed in chapter 3 but in this chapter let us
understand the basic operation of such a system
14 Basic Operations of Queuing System
There are two processes that affect the queuing system (birth process death process) To
explain the operation of the Queuing system we have to take each process independently and
show how the state of the system changes
To have a clear understanding of the operation of the Queuing System Let us assume that
it is installed in bank
When a customer enter the bank (birth occur) he will press on some key on the
numbering unit board or in some cases touch a sensitive screen then the Numbering unit
transfer the data to the server which make a calculations depend on two things first the number
of teller and customer in wait also on the profile and statistical data provided by the
programmer Then the server send information to the numbering unit contain the number of the
customer and the expected waiting time then it will print these information on a ticket also at
the same time the server communicates with Tellers units and Main LCD
However when a customer is served teller unit transfer data to the server which is
transfer these data to the main LCD so as a result a new customer is forwarding to the teller unit
The Figure [1-1] shows a simple graph for the Wireless Queuing System
4
Figure [1-1] Queuing System Configuration
15 Advantages of Queuing System [1]
Even though Queuing Systems improve the service quality in the company there are
several advantage of the use of such a system which are listed below
A) Reduction the waiting and service time for customers
Since the use of Queuing System avoid the dissatisfaction the service personal will work
in free conditions and he will served the customers efficiently so as a result the reduction of the
service and waiting time is achieved
B) Forward the customer to other operator
The use of such a system make it possible to forward the customer to other teller when
the first one is busy
C) Possibility to give a priority for a certain customer (Gold Customers)
In addition the Queuing system gives the flexibility to give a priority to certain
customers such as VIP person
D) Company manager can get report including statistical data
5
Also as a company use the Queuing System the manger can get statistical data this data
including the number served waiting time service rate and employee work loadhellipetc
This data give the manager indications to increase or decrease the number of employee
change the scenario on which the employee served the customers and other things related to the
company
E) The main display unit can not only show the information to the Queuing System but
also it can use to show the date and time and other advertising
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
II
3-2 Terminal Unit
3-3 Main Display Unit
3-4
3-5
3-6
3-7
3-8
3-9
3-10
Counter Display Unit
TRONIX Wireless Queuing System
Automatic Queue Management System (AKIS)
LONBON Wireless Queuing Machine
Servicing the Customer
Practical System Connected Wirily
Practical System Connected Wirelessly
Chapter 4
4-1
Expected 80211a 80211b and 80211g Data Rates at
Varying Distance from Access Point
4-2 80211g Behavior in Different Environments
4-3 OFDM System Transmit Data on Multiple Subcarrier
4-4a Serial to Parallel Conversion
4-4b
4-5
4-6
4-7
4-8
4-9
4-10a
4-10b
OFDM Spectrum
Equivalent generation of OFDM signal
16-QAM constellation diagram
OFDM output with QAM incorporate
80211g OFDM carrier assignments
Simple OFDM Transmitter
OFDM Transmitter
OFDM Receiver
Abstract
III
Queuing systems are one of the most successful organizing techniques which are
used almost in every public place such as hospitals libraries sport centers museums
banks shopping centers and governmental institutions in order to spare peoples time and
effort by controlling and arranging their entrance waiting and servicing In this project
we will introduce all theoretical information and data needed to build a wireless queuing
system
The operation of such systems depend on the teller devices that will transmit
information to display units or LCDs through wireless channels also a server that saves
the readings and calculate every parameter that serves the customer such as number of
customers in the system or the queue waiting time service time and average time spent
in the system
The first part of this project focuses on studying the characteristics of queuing
systems and describing various models that implements them which contributes
significantly to improve the service quality in a customer oriented establishment
Furthermore statistical analysis can be adopted to achieve our goal such as Poisson-
Distribution Exponential Distribution and some measures of random variables
The second part deals with hardware devices which will generally be used to
construct the overall wireless queuing system These parts mainly consist of the Entrance
Numbering Unit the Teller Units and the Display Units A brief research on cost
availability and quality of components is taken into consideration Wireless techniques
are also introduced in order to be able to connect our system wirelessly for moving
purposes
MATLAB language program is used to illustrate some of the above operational and
statistical analysis
المستخلص
IV
ف اذس أ اصف أحذ أوثش ذماخ ارظ ااخحح اسرؼح ذمشثا ف ؼظ األاو االرظاسظا
ح اؼا ج شاوض اشاظح اراحف اثن شاوض ث اسرشفاخ اىرثاخ اؼا ساخ ق اؤطارس
ج ره ى ذفاحى خذر رظاساذشذة دخ اط الد ادذ ػ طشك س ػى ا
ف صف ارظاسظا اءةا حراج ار جي اؼاخ اثااخ اظشين لذط اششعف زا ح
السى
احذاخ ػشضحذاخ اي إى ؼاخ ذشس ار اإلخثاس أداخ ػى األظح ز ث ػ ػرذي
حسةي امشاءاخ فش ازي خاداي أعا االسى لاخ خالي ػذد ث اضت جخذي ا حراخ و
اظا ف اسره لدرسط اي خذحاي لد رظاساال ص اطاتس أ اظا ف اضتائ
طثمح ارج صف صفاي ظا ف الرظاسا خصائص دساسح ػى اششع زا األي ادضء شوض
صتؤسساخ ار ذخ اي اخذح ػح ذحس ف حظ تشى ذسا ز األظح خرفح
تؼط أس ذصغ تض ذصغ ث ذفا إحصائ ذح سم تؼ ره إى تاإلظافح
اؼشائ ارغش ػاخ
صفاي ف رظاساال ظا ثاء سرؼسد ياد األخضج داخاأل غ اششع اثا ادضء رؼا
ع لصش تحث اؼشض حذاخ خثاساإل حذاخ اذخ حذج اؼذ ػى ذش األخضاء ز االسى
اخ ػح ارافش اىفح ى أعا ذمذسف السىاي ذماخ االػرثاس تؼ ذؤخز سف اى
السى يتشه ظاا إصاي ػىساػذا خ
سسرخذ ف زا اششع تشاح ااذالب رحمك افا اظشح اإلحصائح
1
Chapter 1
Introduction to Wireless Queuing System
2
11 Queuing System
Queues build up in the institutes and companies that cater to large number of customers
where the customer service is necessary and the arrival rate to queue is larger than the service
rate Long time of waiting is unpleasant to customer and his service and therefore long queues
damage the company‟s image
Queuing System contributes significantly to improve the service quality in any customer
ndashoriented company Queuing System is ideal for bank university counter hospital and payment
center Queuing System avoid the dissatisfaction customer simply take a site where waiting his
turn to be served or reading advertisements
12 Why Wireless Queuing System
In this project we will build a practical Wireless Queuing System the use of the wireless
in the transfer of data is one of the major purposes of this project
Wireless network is commonly associated with a telecommunications network whose
interconnections between two nodes is implemented without using wires otherwise it is
implemented via some type of remote information transmission system that uses the EM waves
Such as radio wave
Our selections of the wireless refers to the features of this method of transfer data the
advantages using wireless rather than use another method are listed below
A) The addition of additional wires or drilling a new hole in office could be prohibited
impractical or too expensive
B) Flexibility of locations and data port required
C) Keep the look of the company nice
3
13 Basic Components of Queuing System
Queuing System consists from Server (PC) Entrance Numbering Unit Teller Unit
Display unit or Main LCD and other small LCDs
The components of Queuing System will discussed in chapter 3 but in this chapter let us
understand the basic operation of such a system
14 Basic Operations of Queuing System
There are two processes that affect the queuing system (birth process death process) To
explain the operation of the Queuing system we have to take each process independently and
show how the state of the system changes
To have a clear understanding of the operation of the Queuing System Let us assume that
it is installed in bank
When a customer enter the bank (birth occur) he will press on some key on the
numbering unit board or in some cases touch a sensitive screen then the Numbering unit
transfer the data to the server which make a calculations depend on two things first the number
of teller and customer in wait also on the profile and statistical data provided by the
programmer Then the server send information to the numbering unit contain the number of the
customer and the expected waiting time then it will print these information on a ticket also at
the same time the server communicates with Tellers units and Main LCD
However when a customer is served teller unit transfer data to the server which is
transfer these data to the main LCD so as a result a new customer is forwarding to the teller unit
The Figure [1-1] shows a simple graph for the Wireless Queuing System
4
Figure [1-1] Queuing System Configuration
15 Advantages of Queuing System [1]
Even though Queuing Systems improve the service quality in the company there are
several advantage of the use of such a system which are listed below
A) Reduction the waiting and service time for customers
Since the use of Queuing System avoid the dissatisfaction the service personal will work
in free conditions and he will served the customers efficiently so as a result the reduction of the
service and waiting time is achieved
B) Forward the customer to other operator
The use of such a system make it possible to forward the customer to other teller when
the first one is busy
C) Possibility to give a priority for a certain customer (Gold Customers)
In addition the Queuing system gives the flexibility to give a priority to certain
customers such as VIP person
D) Company manager can get report including statistical data
5
Also as a company use the Queuing System the manger can get statistical data this data
including the number served waiting time service rate and employee work loadhellipetc
This data give the manager indications to increase or decrease the number of employee
change the scenario on which the employee served the customers and other things related to the
company
E) The main display unit can not only show the information to the Queuing System but
also it can use to show the date and time and other advertising
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
III
Queuing systems are one of the most successful organizing techniques which are
used almost in every public place such as hospitals libraries sport centers museums
banks shopping centers and governmental institutions in order to spare peoples time and
effort by controlling and arranging their entrance waiting and servicing In this project
we will introduce all theoretical information and data needed to build a wireless queuing
system
The operation of such systems depend on the teller devices that will transmit
information to display units or LCDs through wireless channels also a server that saves
the readings and calculate every parameter that serves the customer such as number of
customers in the system or the queue waiting time service time and average time spent
in the system
The first part of this project focuses on studying the characteristics of queuing
systems and describing various models that implements them which contributes
significantly to improve the service quality in a customer oriented establishment
Furthermore statistical analysis can be adopted to achieve our goal such as Poisson-
Distribution Exponential Distribution and some measures of random variables
The second part deals with hardware devices which will generally be used to
construct the overall wireless queuing system These parts mainly consist of the Entrance
Numbering Unit the Teller Units and the Display Units A brief research on cost
availability and quality of components is taken into consideration Wireless techniques
are also introduced in order to be able to connect our system wirelessly for moving
purposes
MATLAB language program is used to illustrate some of the above operational and
statistical analysis
المستخلص
IV
ف اذس أ اصف أحذ أوثش ذماخ ارظ ااخحح اسرؼح ذمشثا ف ؼظ األاو االرظاسظا
ح اؼا ج شاوض اشاظح اراحف اثن شاوض ث اسرشفاخ اىرثاخ اؼا ساخ ق اؤطارس
ج ره ى ذفاحى خذر رظاساذشذة دخ اط الد ادذ ػ طشك س ػى ا
ف صف ارظاسظا اءةا حراج ار جي اؼاخ اثااخ اظشين لذط اششعف زا ح
السى
احذاخ ػشضحذاخ اي إى ؼاخ ذشس ار اإلخثاس أداخ ػى األظح ز ث ػ ػرذي
حسةي امشاءاخ فش ازي خاداي أعا االسى لاخ خالي ػذد ث اضت جخذي ا حراخ و
اظا ف اسره لدرسط اي خذحاي لد رظاساال ص اطاتس أ اظا ف اضتائ
طثمح ارج صف صفاي ظا ف الرظاسا خصائص دساسح ػى اششع زا األي ادضء شوض
صتؤسساخ ار ذخ اي اخذح ػح ذحس ف حظ تشى ذسا ز األظح خرفح
تؼط أس ذصغ تض ذصغ ث ذفا إحصائ ذح سم تؼ ره إى تاإلظافح
اؼشائ ارغش ػاخ
صفاي ف رظاساال ظا ثاء سرؼسد ياد األخضج داخاأل غ اششع اثا ادضء رؼا
ع لصش تحث اؼشض حذاخ خثاساإل حذاخ اذخ حذج اؼذ ػى ذش األخضاء ز االسى
اخ ػح ارافش اىفح ى أعا ذمذسف السىاي ذماخ االػرثاس تؼ ذؤخز سف اى
السى يتشه ظاا إصاي ػىساػذا خ
سسرخذ ف زا اششع تشاح ااذالب رحمك افا اظشح اإلحصائح
1
Chapter 1
Introduction to Wireless Queuing System
2
11 Queuing System
Queues build up in the institutes and companies that cater to large number of customers
where the customer service is necessary and the arrival rate to queue is larger than the service
rate Long time of waiting is unpleasant to customer and his service and therefore long queues
damage the company‟s image
Queuing System contributes significantly to improve the service quality in any customer
ndashoriented company Queuing System is ideal for bank university counter hospital and payment
center Queuing System avoid the dissatisfaction customer simply take a site where waiting his
turn to be served or reading advertisements
12 Why Wireless Queuing System
In this project we will build a practical Wireless Queuing System the use of the wireless
in the transfer of data is one of the major purposes of this project
Wireless network is commonly associated with a telecommunications network whose
interconnections between two nodes is implemented without using wires otherwise it is
implemented via some type of remote information transmission system that uses the EM waves
Such as radio wave
Our selections of the wireless refers to the features of this method of transfer data the
advantages using wireless rather than use another method are listed below
A) The addition of additional wires or drilling a new hole in office could be prohibited
impractical or too expensive
B) Flexibility of locations and data port required
C) Keep the look of the company nice
3
13 Basic Components of Queuing System
Queuing System consists from Server (PC) Entrance Numbering Unit Teller Unit
Display unit or Main LCD and other small LCDs
The components of Queuing System will discussed in chapter 3 but in this chapter let us
understand the basic operation of such a system
14 Basic Operations of Queuing System
There are two processes that affect the queuing system (birth process death process) To
explain the operation of the Queuing system we have to take each process independently and
show how the state of the system changes
To have a clear understanding of the operation of the Queuing System Let us assume that
it is installed in bank
When a customer enter the bank (birth occur) he will press on some key on the
numbering unit board or in some cases touch a sensitive screen then the Numbering unit
transfer the data to the server which make a calculations depend on two things first the number
of teller and customer in wait also on the profile and statistical data provided by the
programmer Then the server send information to the numbering unit contain the number of the
customer and the expected waiting time then it will print these information on a ticket also at
the same time the server communicates with Tellers units and Main LCD
However when a customer is served teller unit transfer data to the server which is
transfer these data to the main LCD so as a result a new customer is forwarding to the teller unit
The Figure [1-1] shows a simple graph for the Wireless Queuing System
4
Figure [1-1] Queuing System Configuration
15 Advantages of Queuing System [1]
Even though Queuing Systems improve the service quality in the company there are
several advantage of the use of such a system which are listed below
A) Reduction the waiting and service time for customers
Since the use of Queuing System avoid the dissatisfaction the service personal will work
in free conditions and he will served the customers efficiently so as a result the reduction of the
service and waiting time is achieved
B) Forward the customer to other operator
The use of such a system make it possible to forward the customer to other teller when
the first one is busy
C) Possibility to give a priority for a certain customer (Gold Customers)
In addition the Queuing system gives the flexibility to give a priority to certain
customers such as VIP person
D) Company manager can get report including statistical data
5
Also as a company use the Queuing System the manger can get statistical data this data
including the number served waiting time service rate and employee work loadhellipetc
This data give the manager indications to increase or decrease the number of employee
change the scenario on which the employee served the customers and other things related to the
company
E) The main display unit can not only show the information to the Queuing System but
also it can use to show the date and time and other advertising
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
IV
ف اذس أ اصف أحذ أوثش ذماخ ارظ ااخحح اسرؼح ذمشثا ف ؼظ األاو االرظاسظا
ح اؼا ج شاوض اشاظح اراحف اثن شاوض ث اسرشفاخ اىرثاخ اؼا ساخ ق اؤطارس
ج ره ى ذفاحى خذر رظاساذشذة دخ اط الد ادذ ػ طشك س ػى ا
ف صف ارظاسظا اءةا حراج ار جي اؼاخ اثااخ اظشين لذط اششعف زا ح
السى
احذاخ ػشضحذاخ اي إى ؼاخ ذشس ار اإلخثاس أداخ ػى األظح ز ث ػ ػرذي
حسةي امشاءاخ فش ازي خاداي أعا االسى لاخ خالي ػذد ث اضت جخذي ا حراخ و
اظا ف اسره لدرسط اي خذحاي لد رظاساال ص اطاتس أ اظا ف اضتائ
طثمح ارج صف صفاي ظا ف الرظاسا خصائص دساسح ػى اششع زا األي ادضء شوض
صتؤسساخ ار ذخ اي اخذح ػح ذحس ف حظ تشى ذسا ز األظح خرفح
تؼط أس ذصغ تض ذصغ ث ذفا إحصائ ذح سم تؼ ره إى تاإلظافح
اؼشائ ارغش ػاخ
صفاي ف رظاساال ظا ثاء سرؼسد ياد األخضج داخاأل غ اششع اثا ادضء رؼا
ع لصش تحث اؼشض حذاخ خثاساإل حذاخ اذخ حذج اؼذ ػى ذش األخضاء ز االسى
اخ ػح ارافش اىفح ى أعا ذمذسف السىاي ذماخ االػرثاس تؼ ذؤخز سف اى
السى يتشه ظاا إصاي ػىساػذا خ
سسرخذ ف زا اششع تشاح ااذالب رحمك افا اظشح اإلحصائح
1
Chapter 1
Introduction to Wireless Queuing System
2
11 Queuing System
Queues build up in the institutes and companies that cater to large number of customers
where the customer service is necessary and the arrival rate to queue is larger than the service
rate Long time of waiting is unpleasant to customer and his service and therefore long queues
damage the company‟s image
Queuing System contributes significantly to improve the service quality in any customer
ndashoriented company Queuing System is ideal for bank university counter hospital and payment
center Queuing System avoid the dissatisfaction customer simply take a site where waiting his
turn to be served or reading advertisements
12 Why Wireless Queuing System
In this project we will build a practical Wireless Queuing System the use of the wireless
in the transfer of data is one of the major purposes of this project
Wireless network is commonly associated with a telecommunications network whose
interconnections between two nodes is implemented without using wires otherwise it is
implemented via some type of remote information transmission system that uses the EM waves
Such as radio wave
Our selections of the wireless refers to the features of this method of transfer data the
advantages using wireless rather than use another method are listed below
A) The addition of additional wires or drilling a new hole in office could be prohibited
impractical or too expensive
B) Flexibility of locations and data port required
C) Keep the look of the company nice
3
13 Basic Components of Queuing System
Queuing System consists from Server (PC) Entrance Numbering Unit Teller Unit
Display unit or Main LCD and other small LCDs
The components of Queuing System will discussed in chapter 3 but in this chapter let us
understand the basic operation of such a system
14 Basic Operations of Queuing System
There are two processes that affect the queuing system (birth process death process) To
explain the operation of the Queuing system we have to take each process independently and
show how the state of the system changes
To have a clear understanding of the operation of the Queuing System Let us assume that
it is installed in bank
When a customer enter the bank (birth occur) he will press on some key on the
numbering unit board or in some cases touch a sensitive screen then the Numbering unit
transfer the data to the server which make a calculations depend on two things first the number
of teller and customer in wait also on the profile and statistical data provided by the
programmer Then the server send information to the numbering unit contain the number of the
customer and the expected waiting time then it will print these information on a ticket also at
the same time the server communicates with Tellers units and Main LCD
However when a customer is served teller unit transfer data to the server which is
transfer these data to the main LCD so as a result a new customer is forwarding to the teller unit
The Figure [1-1] shows a simple graph for the Wireless Queuing System
4
Figure [1-1] Queuing System Configuration
15 Advantages of Queuing System [1]
Even though Queuing Systems improve the service quality in the company there are
several advantage of the use of such a system which are listed below
A) Reduction the waiting and service time for customers
Since the use of Queuing System avoid the dissatisfaction the service personal will work
in free conditions and he will served the customers efficiently so as a result the reduction of the
service and waiting time is achieved
B) Forward the customer to other operator
The use of such a system make it possible to forward the customer to other teller when
the first one is busy
C) Possibility to give a priority for a certain customer (Gold Customers)
In addition the Queuing system gives the flexibility to give a priority to certain
customers such as VIP person
D) Company manager can get report including statistical data
5
Also as a company use the Queuing System the manger can get statistical data this data
including the number served waiting time service rate and employee work loadhellipetc
This data give the manager indications to increase or decrease the number of employee
change the scenario on which the employee served the customers and other things related to the
company
E) The main display unit can not only show the information to the Queuing System but
also it can use to show the date and time and other advertising
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
1
Chapter 1
Introduction to Wireless Queuing System
2
11 Queuing System
Queues build up in the institutes and companies that cater to large number of customers
where the customer service is necessary and the arrival rate to queue is larger than the service
rate Long time of waiting is unpleasant to customer and his service and therefore long queues
damage the company‟s image
Queuing System contributes significantly to improve the service quality in any customer
ndashoriented company Queuing System is ideal for bank university counter hospital and payment
center Queuing System avoid the dissatisfaction customer simply take a site where waiting his
turn to be served or reading advertisements
12 Why Wireless Queuing System
In this project we will build a practical Wireless Queuing System the use of the wireless
in the transfer of data is one of the major purposes of this project
Wireless network is commonly associated with a telecommunications network whose
interconnections between two nodes is implemented without using wires otherwise it is
implemented via some type of remote information transmission system that uses the EM waves
Such as radio wave
Our selections of the wireless refers to the features of this method of transfer data the
advantages using wireless rather than use another method are listed below
A) The addition of additional wires or drilling a new hole in office could be prohibited
impractical or too expensive
B) Flexibility of locations and data port required
C) Keep the look of the company nice
3
13 Basic Components of Queuing System
Queuing System consists from Server (PC) Entrance Numbering Unit Teller Unit
Display unit or Main LCD and other small LCDs
The components of Queuing System will discussed in chapter 3 but in this chapter let us
understand the basic operation of such a system
14 Basic Operations of Queuing System
There are two processes that affect the queuing system (birth process death process) To
explain the operation of the Queuing system we have to take each process independently and
show how the state of the system changes
To have a clear understanding of the operation of the Queuing System Let us assume that
it is installed in bank
When a customer enter the bank (birth occur) he will press on some key on the
numbering unit board or in some cases touch a sensitive screen then the Numbering unit
transfer the data to the server which make a calculations depend on two things first the number
of teller and customer in wait also on the profile and statistical data provided by the
programmer Then the server send information to the numbering unit contain the number of the
customer and the expected waiting time then it will print these information on a ticket also at
the same time the server communicates with Tellers units and Main LCD
However when a customer is served teller unit transfer data to the server which is
transfer these data to the main LCD so as a result a new customer is forwarding to the teller unit
The Figure [1-1] shows a simple graph for the Wireless Queuing System
4
Figure [1-1] Queuing System Configuration
15 Advantages of Queuing System [1]
Even though Queuing Systems improve the service quality in the company there are
several advantage of the use of such a system which are listed below
A) Reduction the waiting and service time for customers
Since the use of Queuing System avoid the dissatisfaction the service personal will work
in free conditions and he will served the customers efficiently so as a result the reduction of the
service and waiting time is achieved
B) Forward the customer to other operator
The use of such a system make it possible to forward the customer to other teller when
the first one is busy
C) Possibility to give a priority for a certain customer (Gold Customers)
In addition the Queuing system gives the flexibility to give a priority to certain
customers such as VIP person
D) Company manager can get report including statistical data
5
Also as a company use the Queuing System the manger can get statistical data this data
including the number served waiting time service rate and employee work loadhellipetc
This data give the manager indications to increase or decrease the number of employee
change the scenario on which the employee served the customers and other things related to the
company
E) The main display unit can not only show the information to the Queuing System but
also it can use to show the date and time and other advertising
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
2
11 Queuing System
Queues build up in the institutes and companies that cater to large number of customers
where the customer service is necessary and the arrival rate to queue is larger than the service
rate Long time of waiting is unpleasant to customer and his service and therefore long queues
damage the company‟s image
Queuing System contributes significantly to improve the service quality in any customer
ndashoriented company Queuing System is ideal for bank university counter hospital and payment
center Queuing System avoid the dissatisfaction customer simply take a site where waiting his
turn to be served or reading advertisements
12 Why Wireless Queuing System
In this project we will build a practical Wireless Queuing System the use of the wireless
in the transfer of data is one of the major purposes of this project
Wireless network is commonly associated with a telecommunications network whose
interconnections between two nodes is implemented without using wires otherwise it is
implemented via some type of remote information transmission system that uses the EM waves
Such as radio wave
Our selections of the wireless refers to the features of this method of transfer data the
advantages using wireless rather than use another method are listed below
A) The addition of additional wires or drilling a new hole in office could be prohibited
impractical or too expensive
B) Flexibility of locations and data port required
C) Keep the look of the company nice
3
13 Basic Components of Queuing System
Queuing System consists from Server (PC) Entrance Numbering Unit Teller Unit
Display unit or Main LCD and other small LCDs
The components of Queuing System will discussed in chapter 3 but in this chapter let us
understand the basic operation of such a system
14 Basic Operations of Queuing System
There are two processes that affect the queuing system (birth process death process) To
explain the operation of the Queuing system we have to take each process independently and
show how the state of the system changes
To have a clear understanding of the operation of the Queuing System Let us assume that
it is installed in bank
When a customer enter the bank (birth occur) he will press on some key on the
numbering unit board or in some cases touch a sensitive screen then the Numbering unit
transfer the data to the server which make a calculations depend on two things first the number
of teller and customer in wait also on the profile and statistical data provided by the
programmer Then the server send information to the numbering unit contain the number of the
customer and the expected waiting time then it will print these information on a ticket also at
the same time the server communicates with Tellers units and Main LCD
However when a customer is served teller unit transfer data to the server which is
transfer these data to the main LCD so as a result a new customer is forwarding to the teller unit
The Figure [1-1] shows a simple graph for the Wireless Queuing System
4
Figure [1-1] Queuing System Configuration
15 Advantages of Queuing System [1]
Even though Queuing Systems improve the service quality in the company there are
several advantage of the use of such a system which are listed below
A) Reduction the waiting and service time for customers
Since the use of Queuing System avoid the dissatisfaction the service personal will work
in free conditions and he will served the customers efficiently so as a result the reduction of the
service and waiting time is achieved
B) Forward the customer to other operator
The use of such a system make it possible to forward the customer to other teller when
the first one is busy
C) Possibility to give a priority for a certain customer (Gold Customers)
In addition the Queuing system gives the flexibility to give a priority to certain
customers such as VIP person
D) Company manager can get report including statistical data
5
Also as a company use the Queuing System the manger can get statistical data this data
including the number served waiting time service rate and employee work loadhellipetc
This data give the manager indications to increase or decrease the number of employee
change the scenario on which the employee served the customers and other things related to the
company
E) The main display unit can not only show the information to the Queuing System but
also it can use to show the date and time and other advertising
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
3
13 Basic Components of Queuing System
Queuing System consists from Server (PC) Entrance Numbering Unit Teller Unit
Display unit or Main LCD and other small LCDs
The components of Queuing System will discussed in chapter 3 but in this chapter let us
understand the basic operation of such a system
14 Basic Operations of Queuing System
There are two processes that affect the queuing system (birth process death process) To
explain the operation of the Queuing system we have to take each process independently and
show how the state of the system changes
To have a clear understanding of the operation of the Queuing System Let us assume that
it is installed in bank
When a customer enter the bank (birth occur) he will press on some key on the
numbering unit board or in some cases touch a sensitive screen then the Numbering unit
transfer the data to the server which make a calculations depend on two things first the number
of teller and customer in wait also on the profile and statistical data provided by the
programmer Then the server send information to the numbering unit contain the number of the
customer and the expected waiting time then it will print these information on a ticket also at
the same time the server communicates with Tellers units and Main LCD
However when a customer is served teller unit transfer data to the server which is
transfer these data to the main LCD so as a result a new customer is forwarding to the teller unit
The Figure [1-1] shows a simple graph for the Wireless Queuing System
4
Figure [1-1] Queuing System Configuration
15 Advantages of Queuing System [1]
Even though Queuing Systems improve the service quality in the company there are
several advantage of the use of such a system which are listed below
A) Reduction the waiting and service time for customers
Since the use of Queuing System avoid the dissatisfaction the service personal will work
in free conditions and he will served the customers efficiently so as a result the reduction of the
service and waiting time is achieved
B) Forward the customer to other operator
The use of such a system make it possible to forward the customer to other teller when
the first one is busy
C) Possibility to give a priority for a certain customer (Gold Customers)
In addition the Queuing system gives the flexibility to give a priority to certain
customers such as VIP person
D) Company manager can get report including statistical data
5
Also as a company use the Queuing System the manger can get statistical data this data
including the number served waiting time service rate and employee work loadhellipetc
This data give the manager indications to increase or decrease the number of employee
change the scenario on which the employee served the customers and other things related to the
company
E) The main display unit can not only show the information to the Queuing System but
also it can use to show the date and time and other advertising
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
4
Figure [1-1] Queuing System Configuration
15 Advantages of Queuing System [1]
Even though Queuing Systems improve the service quality in the company there are
several advantage of the use of such a system which are listed below
A) Reduction the waiting and service time for customers
Since the use of Queuing System avoid the dissatisfaction the service personal will work
in free conditions and he will served the customers efficiently so as a result the reduction of the
service and waiting time is achieved
B) Forward the customer to other operator
The use of such a system make it possible to forward the customer to other teller when
the first one is busy
C) Possibility to give a priority for a certain customer (Gold Customers)
In addition the Queuing system gives the flexibility to give a priority to certain
customers such as VIP person
D) Company manager can get report including statistical data
5
Also as a company use the Queuing System the manger can get statistical data this data
including the number served waiting time service rate and employee work loadhellipetc
This data give the manager indications to increase or decrease the number of employee
change the scenario on which the employee served the customers and other things related to the
company
E) The main display unit can not only show the information to the Queuing System but
also it can use to show the date and time and other advertising
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
5
Also as a company use the Queuing System the manger can get statistical data this data
including the number served waiting time service rate and employee work loadhellipetc
This data give the manager indications to increase or decrease the number of employee
change the scenario on which the employee served the customers and other things related to the
company
E) The main display unit can not only show the information to the Queuing System but
also it can use to show the date and time and other advertising
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
6
Chapter 2
Analysis and Performance of Queuing
System
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
7
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
8
21 Introduction
In the previous chapter we introduce the component of the Wireless Queuing System In this
chapter we will show some basic concepts of the Queuing System In this system we have a multiple
server an infinite waiting room exponentially distributed inter-arrival times For which at least the mean
value and the standard deviation is known The service discipline is FIFO
However before starting with the desired system we present some concepts The heart of this
chapter is to derive formulas for the expected waiting time
22 What Is the System [1]
Let us first introduce the required definitions
System A set of objects joined to accomplish some purpose
Events Object of interest in the system
Attribute Property of an entity
Activity Predefined set of actions in a specified time period
State of system Collection of variables that describes the system at any time
Event Instantaneous occurrence that may be associated with change of system state
Delay Duration of time of unspecified length which is not known until it ends
Event notice Record of an event to occur at some present or future time along with the
associated data
Event list List of event notices (Future Event List FEL)
List A collection of associated entities ordered in some logical fashion
More and more understanding of these concepts is obtained by applying these previous
concepts to our system
A) Entities server queue
B) State
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
9
1- Number of units (customers for the bank example) in the system Q
2- Server status busyidle S = B I
C) Events In the analysis of the Queuing System we interested in two events Arrival
and Departure
D) Simulation Clock tracks simulated time
E) Actions Different actions depending on the type of the event and the current system
state
23 Types of Queuing System[1]
Queuing System is widely classified into one of the following type
1) Open-type System In open-type system customers arrive from outside and depart to
outside
2) Closed-type System There are no customers arrive from outside and depart to
outside All customers operate internally
Remark1 In our case we desired in the first type (Open-type)
24 Queuing System Characteristics[2][4]
In order to get the analysis of the Queuing System Firstly we have to investigate the
characteristics of such a system The characteristics of the Queuing System are discussed below
A) Calling populations calling population may be finite and infinite
Finite Customers in queue have reduced the available size of population and so
as a result causing a reduction in the arrival rate
Infinite Customers already in the queue do not influence the arrival rate process
B) System Capacity There may be a limit on the queue size When a customer arrive and
find the queue full will return to the calling population Other scenario may be found
Since the system capacity may be limited some customer will not be served and they will
go outside let us take the following definition
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
10
Effective arrival rate number of customers who arrive and enter the system (are served
or are waiting in queue to be served) per unit time
C) Arrival process specified in terms of inter arrival time between successive customers
Arrival may occur at deterministic or at random times The random one is given by
probability density function (PDF) The customers may arrive one a time or in batches
that can be constant size or variable size Usually the Poisson arrival process is used to
implement the arrival process
D) Queue Discipline there are various scenarios for this queue discipline we will take
some of them
I FIFO first-inndashfirstndashout
II LIFO last-in-first-out
III SIRO service in random order
IV SPT shortest processing time first
V PR service according to priority
Remark 1 FIFO and PR are mostly used in queuing system Also we can use both in the same
system as in our desired system
Remark 2 FIFO means that the first in is taken first however the discipline may be not depend
on the order of the customer since the service time is different
25 Birth Death Process[1]
Assume that a Queuing System in state S _n where n is the number of customers in the
system The system can only transition to S_n-1 or S_n+1
Death process Is the process where one customer is departed from a system The system is then
described by S_n-1
Birth process Is the process where one customer is entered to the system The system state is
given by S_n+1
The block diagram shown in the figure below are describe both the Arrival and the
Departure
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
11
Figure [2-1] Flowchart for Departure Process
Figure [2-2] Flowchart for Arrival Process
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
12
26 Queuing Behavior[2]
Customer behavior while standing in a queue line is different
Balk Incoming customers may leave when they see that the line is too long
Renege Leave after being in the line when they see that the line is moving
slowly
Jockey Move from one line to another if they think they have chosen a slow line
27 System Statistics[1]
In this section we will introduce some formulas needed to estimate the parameters of the
Queuing System such as waiting time service timehellipetc These parameters required in the
distributions that modeling the arrival and the departure processes
Average time between arrivals = (sum of all inter-arrival times) (number arrivals
-1)
Expected time between arrival E(T) = tp(t)
Average service time = (total service time) (total number of customers)
Average waiting time = (total waiting time in queue) (number of customers who
wait)
Average time spent in the system = (total time that customers spend in the system) (total
number of customers)
Average time in queue+ average time in service = average time spent in the
system
Probability that a customer has to wait in a queue
P (wait) = (number of customers that wait) (total number of customers)
Fraction of idle time for server
P (idle) = (total idle time) (total simulation time)
Let us take a queuing system work in a bank as an example Figure [2-3] shown below
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
13
The data in this example are collected for 20 customers enter the bank in a period
of time see Table [2-2] then we do some calculations needs to show the customers behaviors
and the servers behaviors
In this system the service policy stat that if both teller are idle Teller 1serves the
next customers otherwise the customer is served by the next available teller
If the service time distribution is specified as in the Table [2-1]
Service time(min) probability Cumulative probability
3 035 035
4 025 060
5 020 080
6 020 100
Table [2-1] Service Time Probability
Figure [2-3][1] Bank Queuing System
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
14
Customer
Arrival
time
Service
time
Time
service
begins
T1
Time
service
ends
T1
Time
service
begins
T2
Time
service
ends
T2
Time
in
Queue
Idle
time
T1
Active
time
T2
1 0 4 0 4 0 0 0
2 8 1 8 9 0 4 0
3 14 4 14 18 0 5 0
4 15 3 15 18 0 0 3
5 23 2 23 25 0 5 0
6 26 4 26 30 0 1 0
7 34 5 34 39 0 4 0
8 41 4 41 45 0 2 0
9 43 6 43 49 0 0 6
10 46 5 46 51 0 1 0
11 47 4 49 53 2 0 4
12 48 3 51 54 3 0 0
13 53 4 53 57 0 0 4
14 59 3 59 62 0 5 0
15 62 5 62 67 0 0 0
16 70 4 70 74 0 3 0
17 71 4 71 75 0 0 4
18 73 1 74 75 1 0 0
19 77 5 77 82 0 2 0
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
15
20 82 4 82 86 0 0 0
Total 6 32 21
Table [2-2][1] Data Related to 20 Customers
We can use the formulas discussed above to calculate the desired parameters
We have to see other options for the service policy
If both teller flip a coin and randomly choose one to service the next customer
Add a new teller to serve only preferred customers (priority)
Two separate line
Two queuing times one for regular customers the other for the preferred
customers
We can add a more rapid teller with high salary instead if slower tellers
28 Queuing System Modeling[3]
In the previous sections we introduce some concepts needed to analysis the Queuing
System and we take simple example of such a system In this chapter we will introduce
important branch in the studying of the Queuing System which is the Queuing System
Modeling The model of the Queuing System enables us to derive formulas to calculate expected
waiting time which is the heart of this chapter
Arrival process
In section 24 we see that customer may arrive one at a time or in batches
Also in our system the arrival of the customer occur randomly which is described by
Poisson distributions
Poisson process
A Poisson process is a counting process N(t) for t ge 0 where N(t) is the number of
events occurred in the interval [0t] if arrival happens once at a time N(t) has stationary and
independent increments and the probability of K arrivals in [0t] is
P (N(t) = k) = λt k lowast eminus λt
k k=0 1hellip (2-1)
Useful properties of the Poisson process
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
16
1) Random splitting
The arrival process for two types of arrivals X and Y are Poisson with rates
λX = λ P and λY = λ (1-p) (2-2)
2) Pooling of more than one arrival stream
The arrival process will be Poisson with rate equal to the sum of all rates
arrived
λ = λki=1 i
(2-3)
Figure [2-4] shows the PDF for the Poisson distributions
Figure [2-4] PDF for Poisson Distributions
And Figure [2-5] shows CDF for Poisson distributions
0 5 10 150
005
01
015
02
025
03
035
04
K
P(X
=K
)
PDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
17
Figure [2-5] CDF for Poisson Distributions
For more details see Appendix A
Service process
Service process can be described using probability density function (PDF) which in our
case the exponential distributions with mean E(X) = 1 (μ) and variance Var(X) = 1 μ 2
Let us noting some properties
μ is the average service time
Exponential PDF is given by
F(x) = μ e- μx
xge 0 and 0 other wise (2-4)
Mean E(X) =1 (μ) (2-5)
Variance Var(X) = 1 μ 2
(2-6)
f(x) is strictly decreasing of x
Lack of memory actions are independent of each other The serving of adjacent
customers is independent
Memory-less property P(X gt s+t Xgts) = P(X gt t) (2-7)
Conditional property for two events A B
0 5 10 150
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Poisson Distribution
lamda=5
lamda=1
lamda=9
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
18
P(AB)=P(A B)P(B)=P(B A)P(A) (2-8)
And we can show that the memory-less property for random of the exponential random
variable
P(X gt s+t X gt s) = P(X gt 119904+119905 119883 gt 119904)
P(Xgt119904)
= eminus λ t+s
eminus λ s
= e- λt
(2-9)
See Figure [2-6] which shows the sketch of the PDF for different value of μ
Figure [2-6] PDF for Exponential Distributions
Also Figure [2-7] shows the sketch of CDF of the exponential distributions
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
PDF for Exponential Distribution
mu=5
mu=1
mu=9
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
19
Figure [2-7] CDF for Exponential Distributions
29 Queuing System Notation[1]
Usually we use the notation for the simplification purposes Queuing system also can be
described using notations In this section we will introduce these notations and we will take
some systems and describing them using these notations
A B X Y Z
A Describes the inter-arrival time distributions
B Describes the service time distributions
X Number of parallel server
Y System capacity
Z The size of calling population
0 2 4 6 8 10 12 14 16 18 200
01
02
03
04
05
06
07
08
09
1
K
P(X
=K
)
CDF for Exponential Distribution
mu=5
mu=1
mu=9
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
20
Notation for A and B
I M exponential or Poisson distributions
II D deterministic constant
III G general arbitrary
Remark If the system capacity and the size of calling population are infinite then Y Z
can be dropped from the notation
So in our desired system the notation contain A B X
A can be replaced by M since Poisson
B can be replaced by M since exponential
X is the number of servers or tellers in our system
As a result the system is finally described by MMX
Remark Exponential distributions are related to the Poisson distributions
If the interval between generation of events (eg arrival service) is an exponential
random variable with mean 1 λ then the event generation process is a Poisson process with
mean λ
ndash Example If buses arrive at the station at intervals that are exponentially distributed the
arrival process for the buses is Poisson
So we can referred to both exponential and Poisson distributions by M in the notation
There are other notations for the Queuing system and we listed these notations in table [2-3]
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
21
Table [2-3] Notations of Queuing System
210 Littlersquos Law[1]
Little‟s law or conservation equation stats that the average number of arrivals at a given
time multiplied by the average total time in the system per number of arrivals equals the average
number of customers in the system or in another words average number of customers in the
system at random interval of time equals the arrival rate times average time spent in the system
Pn Steady-state probability of having n customers in the system
Pn(t) Probability of n customers in system at time t
λ Arrival rate
λe Effective arrival rate
μ Service rate of one server
ρ Server utilization
An Inter-arrival time between customer n and n-1
Sn Service time of the nth arriving customer
Wn Total time spent in the system by the nth arriving customer
Wn
Q
Total time spent in the waiting line by the nth arriving customer
L(t) Number of customers in system at time t
LQ(t) The number of customers in queue at time t
L Long-run time-average number of customers in the system
lQ Long-run time-average number of customers in the queue
W Long-run average time spent in system per customer
WQ Long-run average time spent in queue per customer
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
22
This is a powerful consequence since it is applied almost for every queuing system
regardless of its characteristic
Little‟s law
L = λ W (2-10)
211 Server Utilization[1]
It is a percentage of time measures how much the server is busy and for an infinite
population it must be less than one for the system to be stable
ρ = λ
micro but from stability condition arrival rate ltservice rate
As a result we say that ρlt 1
For a simple queuing system with single server say MM1
ρ = λ
micro (2-11)
And for multi-server like MMX
ρ = λ
xmicro (2-12)
212 Long-run measures of performance[1]
Time average number in system L
Observe the system for period T L (t) = no customers at time t Ti = total time during
[0T] in which the system contained exactly (i) customers
Lav = 1
119879 119894 lowast 119879119894infin
0 = 119894 lowast (119879119894infin0 119879) (2-13)
But 119894 lowast 119879119894infin0 = 119871 119905 119889119905
119879
0
So Lav=1
119879 119871 119905 119889119905
119879
0 (2-14)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
23
Lavrarr L as Trarr infin
Time average number in system LQ
For the same reason as above
LQav = 1
119879 119871119876 119905 119889119905
119879
0 (2-15)
LQavrarr LQ as Trarr infin
Average time spent in system by customer
Similarly Wav=(1N) 119882119894infin119900 (2-16)
Wavrarr infinW as Trarr infin
N Number of arrival during [0 T]
Average time spent in queue by customer
Similarly WQav = (1N) 119882119876119894infin119900 (2-17)
WQavrarr infinWQ as Trarr infin
N Number of arrival during [0 T]
213 Steady-state behavior of infinite-population Markovian
models[1]
In order to have a clear understanding of the system we have to investigate the behavior
of it in the steady-state
In this system we have the following properties
I Infinite population the arrival rate not influenced by the customers already in the
system
II Queuing discipline is FIFO
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
24
Steady ndashstate system state the number of customer in the system is independent of time
The system in the steady-state is referred as a statistical equilibrium
P (L(t) = n) = Pn(t)= Pn (2-18)
Remark If a system is stable it will approach equilibrium state regardless of the initial
state And once the equilibrium is reached the system will remain in it
Let us list the formulas describe the system behavior in the steady-state (desired state)
A) Average number of customer in the system is given b
L= 119899119875119899infin0 (2-19)
B) Average customer time in the system by using little‟s law
W=L
λ (2-20)
C) Average number of customer in queue is given by
LQ=WQ λ (2-21)
D) Average customer time in queue
WQ=W-1 μ (2-22)
Steady-state formulas for MG1 with mean service time 1micro and service variance σ2 are listed
in table [2-4]
Equation Parameter
λmicro ρ
ρ + ρ2(1+σ2micro2)
2(1minusρ)
L
1micro + λ(σ2+ 1micro2)
2(1minusρ)
W
W ndash 1micro Wq
ρ2(1 + σ2micro2)
2(1 minus ρ)
Lq
(1-ρ) P0
Table [2-4] Formulas for MG1
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
25
Steady-state formulas for MM1 with arrival rate λ and service mean 1micro are listed in Table [2-
5]
Equation Parameter
λmicro ρ
ρ
(1minusρ)
L
1 (micro - λ) W
W ρ Wq
λ Wq Lq
(1-ρ) ρn Pn
Table [2-5] Formulas for MM1
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
26
Chapter 3
Queuing System Components
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
27
31 Introduction
In this chapter we will introduce some information about the hardware devices used in
building either wirelessly connected or wired queuing systems and these information will help
us later choose the appropriate equipments and sets used to design manufacture and install full
system completely
Banking machines manufactures and companies try always to improve such systems at
the beginning they built very simple systems which were connected using cables and that
affected the range of freedom the customer have then although they are technologically
advanced wireless types were improved for making movement easier and simplifying the
service
Common industrialization through these companies exists when building the system The
Entrance Numbering Unit or known as the Ticker Dispenser is one of the main devices then we
have the Teller Units or known as Terminal devices the Display Units which consists of special
types of LCDs with different implementations the server that has software running on it for
calculation and service issues
Different examples will be given for each part describing the interfaces between them
how they work and the suitable choice we should take
32 Entrance Numbering Unit[5]
Improvement of service quality and speeds it up with getting the customer satisfaction
can be achieved first by using the Entrance Numbering Unit which is a ticket dispenser that
dispense a ticket for the customer immediately after using it and displays information on that
ticket necessary for who people who need service like the expected waiting time average
waiting time number of customers and at which counter one should go to be served after his
number appears on the main display
The unit consists of
A number of bush buttons for selecting the type of service
Thermal printer
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
28
Two cables one of them used as a power cable the other for transferring data
Wireless connection may be used instead of this data cable but transmitting data will be slower
The figure below shows a ticket dispenser which is a part of the AQMS-16 system
Figure [3-1] Token Dispenser Unit
33 Teller Units[5]
The teller units organize the operation that a customer takes in the institute by calling
him to the counter using a terminal unit connected to the display unit either wirily or wirelessly
and these calling panels usually have a lot of buttons on it for servicing purposes but the most
popular calling method used with this units is by bushing the increment button or the decrement
one to let the customer know that his waiting time in the queue come to an end and he then must
go to the specified counter
The virtual call terminal is an alternative solution of this calling device since a software
program is installed on the employer PC with windows operating system and it can work with
other programs to complete the management
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
29
So this keypad enables the staff to control the flowing of visitors and customers calling
everyone in specific order and forwarding a customer to another casher box or counter if
needed
Figure [3-2] Terminal unit
34 Display Units[5]
It is the most important part in the management queuing system due to the customer
since it leads everyone to the right position when the number of the customer he took from the
card dispenser displayed on this LCD unit put at every counter box Also a main display LCD
mounted on the ceiling appears for all customers and it is necessary for one who is far from the
counter box and cant see his number so this main display shows the required counter and
customer numbers
These LCDs are directly connected to the terminal units by serial cables and the interface
that connect the overall system together in order to receive data from the server or PC software
in the case of having programs manage the process Or they can wirelessly connected by using
the transceiver module and PIC interfacing
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
30
Figure [3-3] Main Display Unit Figure [3-4] Counter Display Unit
A sound box also may be connected to the computer server for better service so when a
teller unit chooses the customer voice played on the speaker calling this customer and it must be
interfaced with amplifier to give load voice
35 Examples and specifications of some practical queuing systems
Companies try always to achieve the best specification for their products by making the
advantages of the system more than disadvantages and try to build the lowest cost system which
is economical for both buyer and supplier and the simplicity of the system must exist regardless
of its complex technology used to build it in order to reduce the staff training also the
independency of operation must exist so that it does not affect other new installed systems or
affected by them
A good reliability of the system must be also taken into consideration it must not be
affected by software upgrades or any computer related issues and the setup of the system must
be easy to maintain by the staff and easier to be supported any time Summary reports is given by
the software to document every operation occurred in the system including the calculation of
different parameters
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
31
We will take examples of queuing systems used all over the world and give some of their
specifications
1) TRONIX WIRELESS QUEUING SYSTEM[6]
This simple system can deal with large number of customers and it is easy to control and
operate with good display It consists of one teller unit one display board and a power adapter
while the display has two 6 high red LED digits set to count from 0099 and the display unit
can be clearly visible up to 100 meter distance
The teller unit uses wireless communication to transmit data to the display unit and has
an INCREMENT-DECREMENT buttons and interfaced with the power adapter in case of low
battery power and has two LED the red one informs us that there is data transmission and the
green one tells us about power
Operation of TRONIX WIRELESS QUEUING SYSTEM
The power adapter is plugged to a 220V power source and then we turn the SWITCH-
ON button on the display unit to display 00 these numbers can be incremented or decremented
by the teller buttons and with every number displayed on the unit there will be a sound indicates
the change of this number
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
32
Figure [3-5] TRONIX Wireless Queuing System
Technical specifications
o Teller Box has a transmitter that can transmit in the range of 15-20 meter for
indoor applications and 30-45 meter for outdoor application with a transmission time 250
millisecond and can be supplies with 9V battery and 12V adaptor Gross weight is 250 gram
with dimensions 38 cm height x 135 cm length x 76 cm width
o Display Board had a receiver with receiving frequency 315 MHz and two red
LED digits H-6 x L-4 with visibility up to 30 meters and supplies from 110220V AC with
power consumption equals to 7 watt Gross weight is 6 Kilogram with dimensions of 267 cm
height x 318 cm length x 9 cm top width 64 cm bottom width
o Power Adapter the input is 220V-560 Hz AC and it supplies 12V DC with
ratings 1000mA The dimensions are 55 cm height x 55 cm length x 7 cm width
2) AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)[7]
This system can provide advanced service for customers to make them very comfortable
and a very relieving situation in working for the worker staff and providing the data for
managers to develop their companys services
Statistical data can contain the customer distribution in the queue the distribution of
service and the average service and waiting times for customers
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
33
Operation of AUTOMATIC QUEUE MANAGEMENT SYSTEM (AKIS)
The customer gets to the ticket dispenser and pushes a key service to get his own number
with the time he may wait until service and waits till his number called without needing to wait
in a line and waste his time The employee working in the system knows whether there are
customers waiting for service and then he pushes the calling key to bring the customer to his
window For every ticket taken the system program registers information to make a full report of
what happening in the system in order to improve the quality by making decisions about workers
who works hard or reducing the number of employees and these reports can be made every day
week or month
Figure [3-6] Automatic Queue Management System (AKIS)
Technical specifications
o Display Unit it has colored LED digits the electric power is 12 watt per
information line and the interfacing is RS-485 The dimensions of information display line are
600 mm x 140 mm x 30 mm
o Ticket dispenser it has push buttons for various types of servicing and a thermal
printer to print the ticket The Gross weight is almost 40 Kilogram and the dimensions are 408 x
1287 x 185
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
34
3) LONBON WIRELESS QUEUING MACHINE[8]
This system is applicable at every institute mentioned before easy to be composed and
very convenient in operation It has a wireless ticket master station ticket-caller virtual caller
window display the main display plasma display wireless Main Control Box and sound box
Operation of LONBON WIRELESS QUEUING MACHINE
Wireless master box receive data from the wireless transceiver module which is located
in the touch screen wireless operating system The LCD touch screen has a printer VIP card
reader and a queue communication and statistics software which can control the information
of the calling display and printer also the software can be changes anytime for the purpose of
upgrading and has many options for calling and tickets
Technical specification
o Touch screen wireless ACD it can be supplied from a 220V AC with ripple
factor 5 and consumes 350 watt and the control signal level ranges from 1V to 5V with baud
rate 9600 bps the thermal printer prints with speed reaches 80MMsecond The gross weight is
41 Kilogram and the dimensions are 600 mm length x 500 mm width x 1350 mm height The
wireless working parameters are 433 MHz RF frequency and 192 KHz data rate using half-
duplex FSK with transmission distance up to 50 meter
o Wireless main control box it has six output ports with RJ45 socket and can be
connected to the parts included in the system and it has a speaker output port 24V DC 63A
switch power supply is attached to it and operates with 24V DC 220V AC The dimensions are
253 mm length x 74 mm width x 233 mm height
o Ticket station it is wirelessly connected to the main control box and has three
buttons Next Last and Re-Call The dimensions are 135 mm length x 75 mm width x 40
mm height
o Main LCD display 42 LCD which can display 6 calling numbers
o Other parts like window dot matrix display relay box sound box ceiling
speaker VIP card and paper roll
o
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
35
Figure [3-7] LONBON Wireless Queuing Machine
36 Connection of the System
To summarize the operation and tell how the system works first the customer comes to
the entrance of the institute and presses a button on the entrance unit to take a ticket and the
counter number required for service appears on the main LCD then the customer goes to the
counter displayed and get served after his number called with a speaker and after he got served
the operator working at the counter presses the increment button on terminal or manipulator unit
to define and the number of the next customer in queue appears on the main LCD again
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
36
Figure [3-8] Servicing the Customer
The whole practical system is connected as follows
Figure [3-9] Practical System Connected Wirily
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
37
Figure [3-10] Practical System Connected Wirelessly
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
38
Chapter 4
Wireless Technology
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
39
41 Introduction
A wireless local area network (WLAN) is two or more computers joined together using
radio frequency (RF) transmissions unlike the wired LAN which uses cabling to link computers
together
Using wireless technology simplifies the aim of networking it enables multiple computer
users to share resources in a home or business without the need to use wires These resources
might include Internet connection network printers data files and even audio and video files
This kind of sharing has become more practical by making computer users change from using
single stand-alone computers to working on networks with multiple computers
It is very important to notice that WLANs are typically an extension to wired LAN they
might be slower than wired LANs (the nominal data transfer rate in WLANs is between 11 and
54Mbps compared to most wired LANs which operate at 100Mbps or 1000Mbps) But they have
a great advantage of eliminate the need of wires which might cause problems in some situations
Moving data through a wireless network involves three separate elements the radio
signals the data format and the network structure In our project we will focus on the network
structure which includes the wireless network interface adapters and base stations that send and
receive the radio signals The network interface adapters in each computer and base station
convert digital data to radio signals which they transmit to other devices on the same network
and they receive and convert incoming radio signals from other network elements back to digital
data
There are several wireless technologies in existence but most wireless LANs use
wireless Ethernet technologies based on IEEE 80211 standards
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
40
42 WLANs Characteristics
Advantages
o Fast and Simple Network Set-up there are no cables to install at a user‟s desk or
work area Placing wires or drilling new holes in a home or office could be hard in some
situations such as
- It could be prevented because of rental regulations
- If the work area consists of several buildings
- In historic buildings where placing cables would be difficult
- It could be very expensive
o Flexibility it is typically easier and quicker to add or move devices on the
network (wired LAN is difficult to move and expensive to change)
o Roaming capability a user can stay connected to the network from almost
anywhere inside or outside a home or business depending on the network coverage
o Cost reduction WLANs reduce the cost because there is no need for cables
o Scalability network expansion and reconfiguration is very simple it can be done
by adding more access points
o Small dynamic ad hoc networks can be created very quickly and relatively easily
Disadvantages
o Limited data rate (maximum of 54Mbps)
o Increasing the number of users will decrease the data transfer rate for each device
o Some devices could not be compatible with each other due to the different
wireless standards which mean that we might need to replace some equipments
o Security is more difficult to guarantee
o Coverage of the network is limited due to existence of walls This will force us to
use more access points which mean higher cost
o In practice a wireless LAN is not a complete solution and will still need a wired
LAN to provide a network backbone
o Data speeds drop as the user moves further away from the access point
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
41
43 Wi-Fi Technology [9]
Wi-Fi stands for Wireless Fidelity Wi-Fi is based on the IEEE 80211 family of
standards and is primarily a local area networking (LAN) technology designed to provide in-
building broadband coverage
The 80211 standard is defined through several specifications of WLANs It defines an
over-the-air interface between a wireless client and a base station or between two wireless
clients There are several specifications in the 80211 family
o 80211 This standard defines the basic wireless LANs and provides 1- or 2-Mbps
transmission in the 24-GHz band using either frequency-hopping spread spectrum (FHSS) or
direct-sequence spread spectrum (DSSS)
o 80211a This is an extension to 80211 that pertains to wireless LANs and goes
as fast as 54 Mbps in the 5-GHz band 80211a employs the orthogonal frequency division
multiplexing (OFDM) encoding scheme
o 80211b This standard gives a data rate up to 11Mbps (with a fallback to 55 2
and 1 Mbps depending on strength of signal) in the 24-GHz band The 80211b specification
uses only DSSS
o 80211g This standard gives the same data rate as 80211a (54Mbps) while
working in the same frequency range as 80211b (24GHz) for backwards compatibility (the best
of the two standards)
Choosing a Service
Our choice of which standard to apply in our project must subject to many factors such
as equipments we are using the size of area to be covered by the network the number of users
to support the applications to be used on the network environmental conditions speed (data
rate) security reliability ease of use and cost
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
42
This is a technical comparison between Wi-Fi standards
WiFi (a) WiFi (b) WiFi (g)
Standard 80211a 80211b 80211g
Frequency (GHz) 5 24 24
Speed (Mbps) 54 11 54
Range (m) 50 100 100
Table (4-1) Comparison between WiFi standards
In our project we are building a wireless network for a bank we choose the standard of
80211g because
o Its coverage area is perfect for our purpose
o The most important factor we are interested in is the speed (data rate) and this
standard offers the best data rate possible for a WLAN
o It is backwards compatible with 80211b equipments since they are operating at
the same frequency band
44 80211g Performance and Characteristics[11]
80211g Data Rates
The 80211 standard technologies support different data rates to allow clients to
communicate at the best possible speed When a client selects a data rate it considers obtaining
the highest possible speed and trying to minimize the number of communication errors When an
error occurs in data the system must spend time in retransmission of data until it is error free
Each 80211 client performs a procedure to select the best data rate The 80211g clients can
select from the widest possible range of both OFDM data rates of 54 48 36 24 18 12 9 and 6
Mbps and the CCK rates of 11 55 2 and 1 Mbps
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
43
80211g Range
As distance from the access point increases 80211 based products reduce data rates to
maintain connectivity The 80211g standard has the same propagation characteristic as 80211b
because they both act on the same 24 GHZ frequency band Because 80211b and 80211g
products share the same propagation characteristics we can get the same maximum range at the
same data rate Because 5-GHz radio signals do not propagate as well as 24-GHz radio signals
the 80211a product range is limited compared to the 80211b or 80211g product range
The following figure shows the expected data rate of the different 80211 standards at
different ranges
Figure (4-1) Expected 80211a 80211b and 80211g Data Rates at Varying Distance from
Access Point
NETWORK ENVIRONMENT CONSIDERATIONS
One of the major benefits of the 80211g standard is the ability of 80211g and 80211b
devices to communicate with each other At all 80211b low data rates 80211b devices
communicate with 80211g products as if they were 80211b products However 80211g
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
44
products behave differently when using OFDM high data rates if there are 80211b devices in the
network environment This is a short discussion of this behavior
80211g-ONLY
When the access point and all clients are 80211g communication occurs at the highest
possible data rate The 80211g AP detects that all of the clients are 80211g and inform the
network not to use any protection method
80211g AP MIXED CLIENTS
When the AP is 80211g and there is a mixture of 80211g and 80211b clients the AP
detects both technologies on the network The 80211g AP instructs 80211g clients to use a
protection mechanism That‟s yields 80211g clients to act at reduced 80211g data rate (up to 15
Mbps) which is faster than the 80211b client that communicates at a maximum rate of up to 58
Mbps
80211b AP 80211g CLIENT
When the AP is 80211b and the client is 80211g the 80211g client is able to
successfully communicate with the 80211b AP Communication between the AP and the
80211g client uses CCK modulation and gives the 80211b speeds An 80211g client can
always act as an 80211b client
Figure (4-2) 80211g Behaviour in Different Environments
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
45
Protection Mechanism Air Traffic Control
The protection mechanism is provided by the 80211g standard to manage
communication in a mixed 80211bg environment The 80211b radios do not hear when the
airspace is busy with 80211g OFDM signals Protection mechanisms prevent 80211b clients
from transmitting if the wireless channel is busy with the 80211g OFDM signals The 80211g
products have the priority and still communicate at the same 80211g OFDM data rates when
protection is in use
45 Wi-Fi Access Protocol
IEEE 80211 wireless LANs use a media access control protocol called Carrier Sense
Multiple Access with Collision Avoidance (CSMACA)
Wi-Fi systems have a fundamental problem that is all stations share the same media
(transmit and receive on the same radio channel) This problem yields that a station
cannot hear while it is sending and hence it impossible to detect a collision Because of this the
developers of the 80211 specifications came up with a collision avoidance mechanism called the
Distributed Control Function (DCF)
According to DCF A Wi-Fi station will transmit only if it thinks the channel is clear All
transmissions are acknowledged so if a station does not receive an acknowledgement it assumes
a collision occurred and retries after a random waiting interval
46 Security standards
Security of the network we are building needs very large amount of interest because our
project (Queuing System) is dealing with people privacy such as finance (in the bank case) or
private information (in service centers case)
Wireless LAN came with a default security mechanism called Wireless Equivalent
Privacy (WEP) WEP uses data encryption to provide a basic level of security for WLAN users
WEP allows the administrator to define an encryption key which is used to encrypt data before
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
46
it is transmitted through the airwaves When WEP is enabled all stations (clients and Access
Points) are required to have the same WEP key Network access is denied to anyone who does
not have the correct key However WEP is very weak mechanism WEP mechanism had been
attacked very much by hackers and they success in beating this mechanism so WEP should be
used if other solutions are not available
80211 developers introduced more efficient mechanisms than WEP such as WPA and
WPA2
WPA (Wi-Fi Protected Access)
WPA incorporates features of the IEEE 80211i standard WPA runs in either enterprise
mode or pre-shared key (PSK) mode
o Enterprise Mode requires an authentication server for authentication and dynamic
key distribution
o Personal Mode (pre-shared key) does not require an authentication server A
shared key is entered once on the access point and the wireless client to act as a starting point for
the dynamic encryption process
WPA includes three main elements
o Authentication using the 8021x protocol (only in enterprise mode)
o Data encryption through Temporal Key Integrity Protocol (TKIP)
o Data validation with Message Integrity Check (MIC)
8021x is a protocol for secure mutual authentication of users and networks 8021x uses
Extensible Authentication Protocols (EAPs) to provide a secure link between the client AP and
Authentication server There are three parts to an 8021x solution
o The supplicant (software on the client device incorporating 8021x and at least
one EAP)
o An authenticator (usually the AP which communicates between the client and
authentication server)
o An authentication server (typically a RADIUS server to validate the client)
WPA allows for several different EAPs to be used EAP-TLS is one of the major versions
that have been tested by the Wi-Fi Alliance but it requires Public Key Infrastructure (PKI)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
47
certificates on the server and clients 8021x is currently not widely implemented in networks
Organizations may wish to consider a plan to move the whole network (wired and wireless) to
8021x authentication
TKIP enhances WEP and securely alters the key with every data packet sent using Per
Packet Keying (PPK) It uses 128 bit encryption although it still employs the same encryption
algorithm used by WEP
MIC provides data validity to prevent accidental changes to data sent across the network
It should be noted though that WPA offers no support for devices in ad hoc mode For
encryption to take place in this mode WEP will still need to be used
WPA280211i
The 80211i security standard provides a very secure mechanism for wireless networks
WPA2 adds a stronger encryption algorithm based on the Advanced Encryption Standard (AES)
It also reduces the number of data packets involved in key management
It is advisable to ensure that all future purchases are WPA2 compliant Due to the
processing demands of AES many older APs will have to be replaced in order to handle
80211iWPA2 However some APs will only need a software upgrade Users will need to check
with the manufacturer to determine whether this is possible
Both WPA and WPA2 can be used in a bdquomixed mode‟ which allows a WPA device to be
backwards compatible with another device using a previous wireless security protocol
Unfortunately this means that if a WPA device interacts with one using WEP this greatly
reduces the security so is not recommended
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
48
47 Modulation[10]
80211g is the latest standard in wireless networking It results from the development
80211a and 80211b combining the speed of 80211a with the low cost and the coverage area of
80211b
80211g will have a high data transfer rate by using the orthogonal frequency division
multiplexing (OFDM) modulation technique that is used in 80211a while maintaining the
timing and frequency arrangements from 80211b
80211g is best understood as the combination of 80211a and 80211b wireless
networking standards 80211g will use the two different modulation techniques of the a and b
systems at 24 GHz which is the operating frequency of 80211b to allow compatibility with
80211b systems and get the same coverage area while keeping the data rate of the 80211a
standard
OFDM is a multi-carrier modulation scheme The data is divided to multiple closely
spaced subcarriers By doing so OFDM systems are able to provide very reliable operation and
high data rates
Figure (4-3) OFDM System Transmit Data on Multiple Subcarrier
Let‟s consider transmitting binary digits at a rate of R bps The bandwidth B required to
transmit these bits is R(1 + r) with r the Nyquist rolloff factor Now consider we have a
sequence of N of these bits stored for an interval TS = NR (the OFDM symbol interval) Then the
system carry out the Serial-to-parallel conversion and each of the N bits stored is used to
modulate a separate carrier signal All N modulated-carrier signals are then transmitted
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
49
simultaneously over the Ts interval Figure (4-4a) shows the operation of OFDM the parameters
ak represent the successive bits stored while the frequencies fk represent the N carrier frequencies
transmitted in parallel Figure (4-4b) shows the resultant OFDM spectrum To make the carrier
frequencies orthogonal to each other it must have the spacing Δf between carriers equal to 1TS
Thus we have B = NΔf where B is the transmission bandwidth as shown in Figure (4-4b) Δf
also represents the bandwidth of each of the N parallel frequency channels
(a)
(b)
Figure (4-4) (a) serial to parallel conversion (b)OFDM spectrum
From the above analysis we conclude that this process has reduced the transmission
bandwidth of each of the transmitted signals by the factor of N Using the previous process of
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
50
transmitting multiple carriers in parallel can yield a problem in implementation of OFDM To
solve this problem we use the discrete Fourier Transform technique
Back to the N parallel output signals of Figure (4-4a) transmitted over a TS interval We
define the total signal transmitted v(t) as the sum of these signals And the kth carrier frequency
fk as [fc +kΔf] 0lekleNminus1 Consider the kth carrier signal to be cos 2π(fc + kΔf)t then v(t) may be
written as
119907 119905 = 119877119890 119886119896 119873minus1119896=0 1198901198952120587 119891119888+119896∆119891 119905
= 119877119890 1198901198952120587119891119888119905 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
= 119877119890 1198901198952120587119891119888119905 119886(119905) (4-1)
With a(t)= 119886119896 119873minus1119896=0 1198901198952120587119896 ∆119891119905
Now we sample a(t) at intervals TSN apart (at the rate of R samples per second) After
sampling we got the sampled function a(n) with t replaced by nTSN And we can substitute Δf
with 1TS Finally we can write a(n) as
119886 119899 = 1198861198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-2)
We note that the previous equation is exactly in the form of the inverse Discrete Fourier
Transform and it may be evaluated using Fast Fourier Transform (FFT) techniques In place of
the transmitting N orthogonal carriers in parallel we can transmit them at the single carrier
frequency using FFT calculation This process is shown in figure (4-5)
Figure (4-5) Equivalent generation of OFDM signal
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
51
This is the procedure that followed in high-speed WLANs At the receiver the process is
reversed for each symbol interval TS the receiver demodulate the received modulated carrier
signal the discrete Fourier Transform is calculated from which the N coefficients ak k = 0 N
minus 1 are recovered and parallel-to-serial conversion used to generate the desired output bit stream
Note that N is chosen as multiple of 2 to help carrying out the FFT calculations
In order to get higher bit rate data signals to be transmitted over a specific bandwidth the
previously discussed process of generating the OFDM signal from binary input samples using
FFT may be generalized to an input of QAM signal samples First QAM is used to reduce the
bandwidth required to transmit a given input bit stream Let K lt N successive binary digits be
stored generating one of 2K possible QAM signals Figure (4-6) show an example of 16-QAM
signals each point in the group represents one of the 2K signals to be transmitted the signals may
be represented as a complex number
Figure (4-6) 16-QAM constellation diagram
Let the kth complex number be ak We carry out QAM generation using each successive
group of K binary digits and then store the resultant N successive complex numbers ak k = 0
N minus 1 over the TS OFDM symbol interval and then use serial-to-parallel conversion to transmit
these N complex numbers over different subcarrier for each We have thus obtained a more
general form of OFDM But in this process we have to notice that we deal with complex
numbers ak in place of the binary coefficient used in equation (4-2)The inverse discrete Fourier
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
52
Transform is again obtained to perform the OFDM operation by sampling the resultant equation
but this time sampling at the QAM intervals( KR units of time apart) Finally we got the more
general case of considering complex coefficients ak in place of the ak coefficients below
119886 119899 = 1199381198961198901198952120587119896119899
119873 119899 = 0 helliphellip119873 minus 1119873minus1119896=0 (4-3)
Inverse Fast Fourier techniques may be carried out to perform the equation (4-3) The
OFDM more general system (working with QAM) operations before carrying out serial-to -
parallel conversion is shown in figure (4-7)The I and Q signals represent the inphase and
quadrature components of the complex IFFT operation (real part imaginary part ak coefficients)
Figure (4-7) OFDM output with QAM incorporate
Physical layer specifications 80211g and 80211a
The IEEE 80211g standard specifies an OFDM physical layer (PHY) that splits an
information signal across 52 separate subcarrier signals to provide transmission of data at a rate
of 6 9 12 18 24 36 48 or 54 Mbps Operation is done over 20-MHz wide bands within the
overall frequency band used In order to provide the desired OFDM operation subcarriers must
be spaced 3125 kHz apart with the equivalent inverse Fourier Transform technique used to
perform the OFDM operation through IFFT techniques
The carrier spacing of 3125 kHz over the 20-MHz band allows 64 subcarriers to be
transmitted over this band But a bandwidth of 166 MHz within the center of the 20-MHz band
is actually used to carry out the OFDM operation 52 subcarriers with equivalent spacing from
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
53
each side of the band center as shown in figure (4-8) are used to cover the 166 MHz band 48
carriers of these 52 are used to carry data and the other four are used to carry pilot information
Figure (4-8) 80211g OFDM carrier assignments
OFDM symbols are defined as 48 complex numbers each representing one of the data
subcarriers The OFDM data rates supported by these standards are 6 9 12 18 24 36 48 and
54 Mbps These eight data rates are obtained by using different combinations of QAM with
OFDM as shown in table (4-2) As we mentioned previously for orthogonal frequency
operation the sub-carrier spacing must be 1TS where TS is the OFDM symbol interval With a
sub-carrier spacing here of 3125 kHz we have TS = 32 microsec
Data Rate
(Mbps)
Modulation Coding Rate Coded bits per
subcarrier
Coded bits per
OFDM
symbol
Data bits per
OFDM
symbol
6 BPSK 12 1 48 24
9 BPSK 34 1 48 36
12 QPSK 12 2 96 48
18 16-QAM 34 2 96 72
24 16-QAM 12 4 192 96
36 16-QAM 34 4 192 144
48 64-QAM 23 6 288 192
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
54
54 64-QAM 34 6 288 216
Table (4-2) Data rates parameters in 80211g
Figure (4-9) shows a simple 80211g OFDM transmitter using the IFFT calculation The
bit rate R is one of the eight bit rates mentioned above Forward-error correction and
convolutional encoder is then carried out Some bits of the output bit stream of this encoder is
deleted (the number depends on the input bit rate) to get the desired output bit rate
Figure (4-9) Simple OFDM transmitter
An interleaver is then used to spread out the modified output stream and the resultant bit
stream stored the appropriate number of bits to provide a QAM symbol Each QAM-
constellation complex number referring to a set of input bits received in the QAM interval is
stored until 48 complex numbers are accumulated for input to the IFFT calculator These
complex numbers are represented by a sequence of I (inphase) and Q (quadrature) numbers in a
32 microsec interval and represented by I and Q in figure (4-9)
These 48 complex numbers which represent the data to be transmitted are augmented by
four numbers corresponding to the four pilot signals A 64-point IFFT is used with 16 of the
IFFT input coefficients set equal to zero The IFFT output is then used to modulate the system
carrier
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
55
The whole operation of transmission and receiving the OFDM signals is represented in
figure (4-10)
(a)
(b)
Figure (4-10) OFDM transmitter (a) and receiver (b)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
56
Conclusion and Future work
In this project we understand the basic concepts that related to Wireless Queuing System
and how this system provide an efficient organizing for the companies and institutes
In the first part of this project we studied all the theoretical and statistical analysis of the
system also we studied all the parameters associated with the system MATLAB codes were
used to implement these parameters
In the second part we learn how the system operates and how it will be interfaced
wirelessly Also we introduce some examples of such a system Wireless technology was
introduced and focused on the Wi-Fi technology in order to help us in the Wireless connection
As a future work we look forward to implement the system practically and making all the
interfacing and the code program that will be used in the server (PC) This is our plan for the
first semester of the Final Graduation Project (EE530) but our plane can be modulated or
changed according to discussion committee
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
57
References
[1] Gross and Harris ldquoFundamentals of Queueing Theoryrdquo 3rd Ed Wiley 1998 (Required)
[2] Banks Carson Nelson amp Nicol ldquoDiscrete Event System Simulation Prentice Hall 2001
[3] Kleinrock ldquoQueueing Systems vol 2 Computer Applicationsrdquo Wiley 1976 (Reference)
[4] httpwwwecestevens-techedu~ccomaniccpe345_05html
[5] httpwwwwikipediaorg
[6] httpwwwinnovatronixcom
[7] httpwwwqms-akiscom
[8] httpwwwlonboncom
[9] Institute of Electrical Engineer (IEEE) wwwieeeorg][wwwwikipediaorg]
[10] Mobile Wireless Communication Mischa Schwartz Department of Electrical Engineering
Columbia University
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
58
Appendix A
A1 MATLAB Code for Exponential Distributions
PDF for exponential x = 0520 y = exppdf(x5) z=exppdf(x1) a=exppdf(x9) plot(xy-r) hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(PDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A2 MATLAB Code of CDF for Exponential Distributions
CDF for exponential gtgt x = 0520 y = expcdf(x5) z=expcdf(x1) a=expcdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(mu=5mu=1mu=9) title(CDF for Exponential Distribution) xlabel(K) ylabel(P(X=K))
A3 MATLAB Code of PDF for Poisson Distributions
PDF for poisson gtgt x = 015 y = poisspdf(x5) z=poisspdf(x1) a=poisspdf(x9) plot(xy-r) gtgt hold
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
59
plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(PDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A4 MATLAB Code of CDF for Poisson Distributions
CDF for poisson gtgt x = 015 y = poisscdf(x5) z=poisscdf(x1) a=poisscdf(x9) plot(xy-r) gtgt hold plot(xz-or) plot(xa-r) grid on legend(lamda=5lamda=1lamda=9) title(CDF for Poisson Distribution) xlabel(K) ylabel(P(X=K))
A5 Histogram of Average Waiting Time
MM1 queue
a = 15 average number of arrivals per minute b = 2 average number of people served per minute ncust = 1000
at = zeros(ncust1) arrival time of a person joining the queue ft = zeros(ncust1) finish time after waiting and being served
Generate random arrival times assuming Poisson process r = rand(ncust1) iat = -1a log(r) Generate inter-arrival times exponential
distribution at(1) = iat(1) Arrival time of first customer for i=2ncust at(i) = at(i-1) + iat(i) arrival times of other customers end
Generate random service times for each customer r = rand(ncust1) st = -1b log(r) service times for each
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
60
Compute time each customer finishes ft(1) = at(1)+st(1) finish time for first customer for i=2ncust compute finish time for each customer as the larger of arrival time plus service time (if no wait) finish time of previous customer plus service time (if wait) ft(i) = max(at(i)+st(i) ft(i-1)+st(i)) end
total_time = ft - at total time spent by each customer wait_time = total_time - st time spent waiting before being served ave_service_time = sum(st)ncust ave_wait_time = sum(wait_time)ncust ave_total_time = sum(total_time)ncust
Plot histogram of waiting times hist(total_time0520)
A6 MATLAB Code to Calculate the Parameter of the Queuing System from
the Entered Lambda and Mu
MM3 (poisson inter-arrival exponential service three servers) queuing
system model with FCFS
lambda = input(Enter lambda ) entering arrival rate
-5 0 5 10 15 20 250
50
100
150
200
250
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
61
mu = input(Enter mu ) entering service rate
x = [ lambda mu] y = [lambda mu] disp(x) disp(y)
rho = lambda(3mu) rho which is the
utilization factor or how busy the servers are Lq = (27rho^4)(6(1 - rho)(1+2rho+15rho^2)) the number of customers
in a queue (waiting) or the average length of a queue L = Lq + 3rho the number of customers
in the system (waiting and served) Wq = Lqlambda the average or mean
waiting time ( customer spend in a queue) W = Llambda the average or mean
time spend in the system (waiting in queue and being served) P0 = (1-rho)(1+2rho+15rho^2) probability that the
system is empty Pn2 = (((lambdamu)^2)P0)2 probability of having n
customers (lets say n=2 lt= servers) in the system (in queue and being
served) Pn6 = (((lambdamu)^6)P0)162 probability of having n
customers (lets say n=6 gt servers) in the system (in queue and being served) Pw = ((lambdamu)^3)(1(1-rho))(P06) probability of an
arriving customer to wait in the queue before being served
A = [ rho L Lq Wq W P0 Pn2 Pn6 Pw] B = [rho L Lq Wq W P0 Pn2 Pn6 Pw] disp(A) disp(B)
k = input(Enter row matrix of values k ) c = 3muWq(1 - rho) probability that P(Wq gt 0) PW3 = exp(-muk)(1 + (c(1 - exp(-2muk + lambdak))(2-3rho)))
calculate P(W gt k) for lambda not equal 2mu PW3eq = exp(-muk)(1 + (cmuk))
calculate P(W gt k) for lambda equal 2mu
F = [ k P(Wgtk)for lambda not equal 2mu] f = [k PW3] disp(F) disp(f)
S = [ k P(WgtK)for lambda equal 2mu] s = [k PW3eq] disp(S) disp(s)
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