Mobile Picture

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Mobile Communication

Services and Systems

Lecture [1]

Basics of Mobile Communication

Mohammed Elmusrati University of Vaasa

References• This course consists of 12 lecture.

• We will use different books and articles for the course materials.

• The main two books are:

– J. Eberspächer, H. Vögel, and C. Bettstetter, GSM, Switching, Services, and Protocols 2nd ed, Wiley (ISBN 0471 49903 X)

– H. Holma and A. Toskala, WCDMA for UMTS 3ed, Wiley (ISBN 0-470-

87096-6)

• Other used material

– J. Korhonen, Introduction to 3G Mobile Communication 2nd ed, ISBN 1-58053-507-0

– A. Mishra, Fundamentals of Cellular Network Planning and Optimization ,Wiley (ISBN 0-470-86267-X)

– R. Steele and L. Hanzo, Mobile radio Communications 2nd ed., Wiley (ISBN0-471-97806-X)

– Understanding Telecommunications parts 1 and 2, (ISBN 91-44-00212-2)

– C. Politis ,Cooperative Networks for the Future Wireless World , IEEEComm. Magazine, Sep. 2004

– There are many reports and articles available on the internet. Just searchusing for example Google.



2

Mobile Communication• The aim of mobile communication systems is to

offer services to customers whenever andwherever the customers are located.

• This requires the provision of radio spectrumover the geographic area to be covered.

• Terrestrial mobile systems aim to achieve thistarget by providing a network of radio stations.This is called Spatial Division Multiple Access

• Such systems are termed “Public Land MobileNetwork” (PLMN)

Mohammed Elmusrati, Telecommunication Group, University of Vaasa, Finland

Mobile Network Evolution

F D M A

AMPS

NMT

T D M

A

IS-136

TDMA

D-AMPSGSM

IMT-DSUTRA FDD/W-CDMA

GPRS

EDGE IMT-SCIS-136HS

UWC-136

HSPA

1G 2G 2.5G 3G 3.5G

C D M A IMT-TC UTRA

TDD/TD-CDMA IMT-TC TD-SCDMA IMT-MCcdma2000 1X EV-DO

IS-95cdmaOne

cdma2000 1X

2.75G

time



3

Evolution• The first-generation System – Started about 1980s, in Nordic countries Nordic Mobile Telephones

(NMT) and in UK Total Access Communication System (TACS).

– .

• The Second-generation System – Started about 1991, it is called in Europe Global System for Mobile

communication (GSM).

– Although the original system designed for voice and low data ratecommunication it has been improved and enhanced for many other types of services.

– The first improvement is GSM with VAS( Value Added Services) whichincludes the addition of two latforms called Voice Mail S stem VMS and Short Message Service (SMS) Center.

– Between 2G and 3G there is no real revolutionary step but the datacommunication has been supported in 2G systems by introducingGPRS which is a packet oriented services at higher data rates. GPRScan be used with all TDMA based systems. EDGE proposed a newmodulation scheme to increase the supported data rates.

– CdmaOne was enhanced to cdma2000 1X to offer higher data rates.

Evolution• The Third-generation System

– The current GSM systems (even with the modifications) will notbe able to fulfill the near future requirements for more efficient

.

– The 3G systems are more efficient and faster than GSM. InEurope it is called UMTS, and in USA it is named cdma2000.There are some differences between the two standards.

– The maximum data rate of the first drafts of the 3G standard wasabout 2Mb/s. By applying minor modifications with usingopportunistic scheduling of the resources the data rate has beenincreased to about 14 Mb/s. This is called High Speed PacketAccess (HSPA). It is based on 3G core, so that it is classified as.

• The Fourth-generation System – The fundamental reason for the transition to the All-IP is to have

a common platform for the technologies that have beendeveloped so far, and to harmonies with the user expectations of the many services to be provided. There are several projectsunder cellular core such as LTE.




4

The OSI Model• The Open System Interconnection (OSI) was

developed by ITU (InternationalTelecommunication Union) to be layered with(almost) independent layers.

• Some benefits of this layering process are: – To separate the various parts that form a

communication system

– To introduce the possibility to modify or even change-

system. – Easy debugging and system verification

– Easy maintainability and future extensibility.


OSI Model

Application Layer Application Layer

Transport Layer

Session Layer

Presentation Layer

Session Layer

Transport Layer

Presentation Layer

4

5

6

e wor ayer

Physical Layer Physical Layer

Data Link Layer

e wor ayer

Data Link Layer

1

3

2




5

OSI Layers• Layer 1: Physical Layer

– e p ys ca ayer s respons e or e ac ua ransm ss on o

data. It transmits the information that it receives from layer 2

without any changes except for the information needed to

synchronize with the physical layer of the next node where the

information is to be sent.

• Layer 2: Data Link Layer – .

the data into packets or frames and send them to the physicallayer for transmission. Layer 2 does the error detection and

correction.


OSI Layers

• Layer 3: Network Layer –

the path that a data packet has to take and the final destination ithas to reach. Thus, this layer gives the routing information for the

data packets.

• Layer 4: Transport Layer – This layer is a boundary between the physical elements and

logical elements in a network and provides a communication.

detection (but no error correction), and can cater for a reducedflow rate to enable re-transmission of data. Thus, layer 4provides flow control, error detection , and multiplexing of theseveral transport connections on one network connection.




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OSI Layers• Layer 5: Session Layer

– .This means that it does the application identification but not themanagement of the application.

• Layer 6: Presentation Layer – This layer basically defines and prepares the data before it is

sent to (or from) the application layer. This layer is responsiblefor encryption/decryption, compression/decompression and

.

• Layer 7: Application Layer – This layer is responsible for matters related to the origin and the

final use of the data.


GSM Architecture

PSTN

NSS

EIR AUC OMC OSS

MSCVLR

MSC

MSC

A interface

VLRBSC

BTSAir interface Um

Abis interfaceBSSuplink

downlinkMS



7

GSM Architecture• The previous slide shows a simplified functional architecture of a

GSM system. It consists of three subsystems, the base station, ,

operation subsystem (OSS).

• Mobile Station (MS): The MS is the user end terminal. It maycontain many functions not necessary to perform calls such asPDA, digital camera, etc. Mainly each MS consists of user independent hard- and software and of the subscriber identitymodule (SIM), which stores all user-specific data that is relevantto GSM. The MS itself can be identified via the international

. identifiers and tables, such as card type, serial number, a list of subscribed services, a personal identity number (PIN), a PINunlock key (PUK), an authentication key Ki, and the internationalmobile subscriber identity (IMSI), and it also contains dynamicinformation such as temporary mobile subscriber identity (TMSI)and the location area identification (LAI).


GSM Architecture

• Base Station Subsystem (BSS)

– The BSS consists of

1) Base Transreceiver Station (BTS)2) Base Station Controller (BSC)



8

GSM ArchitectureBase Transreceiver Station (BTS)

•and the mobile station (MS). Hence, it performs theimportant function of acting as a hub for the wholeof the network infrastructure.MS are linked to the BTS through the air-interface.The major functions of the BTS are transmission of signals in the desired format, coding and decoding

, -

transmission by using equalization algorithms,encryption, measurements of quality and receivedsignal power and operation and management of thebase station equipment itself.

GSM Architecture

Base Station Controller (BSC)• This controls the radio subs stem es eciall the

base stations.

• The major functions of the BSC include

management of the radio resources andhandover.

• It is also responsible for control of thetransmitted power, security configurations andalarms.

• The interface between BTS and BSC is calledAbis.

• The Abis interface consists of 16 or 64 kbit/sconnections.



9

GSM Architecture• Network Subsystem (NSS)

• The main components of the NSS are

– Mobile Switching Centre (MSC)

– Home Location Registrar (HLR)

– Visitor Location Registrar (VLR)

GSM Architecture

– Mobile Switching Centre (MSC):• The MSC is the sin le most im ortant element of

the NSS and it is responsible for the switchingfunctions that are necessary for interconnection

between mobile users and other mobile and fixednetwork users.

• It is like a normal Public Switched TelephoneNetwork (PSTN) exchange, but it needs to takeinto account of the mobility nature of customers.

,components, HLR, VLR, and AUC.

• The Gateway MSC (GMSC) is a normal MSC withthe additional functions necessary to interconnecta PLMN with other networks.



10

GSM ArchitectureHome Location Register (HLR):

– The HLR contains the information related to

each mobile subscriber, such as the type of

subscription, services that the user can use,

the subscriber’s current location and the

mobile equipment status.

– The database in the HLR remains intact and

unchanged until the termination of the

subscription.

GSM Architecture

Visitor Location Register (VLR):

• The VLR comes into action once the subscriber

enters the coverage region.

• Unlike the HLR, the VLR is dynamic in nature and

interacts with the HLR when recording the data of

.

• When the subscriber moves to another region, the

database of the subscriber is also shifted to the

VLR of the new region.



11

GSM Architecture• Operation Subsystem (OSS): The OSS

con a ns e necessary unc ons or

network operation and maintenance and it

consists of

– Operation and maintenance center (OMC)

– Authentication center AUC

– Equipment identity register (EIR)

GSM Architecture

Operation and maintenance center (OMC)

The OMC monitors and controls all other

network entities via the O interface (SS7 with

X.25).

Typical OMC management functions are traffic

monitoring, status reports of network entities,

su scr er an secur y managemen .



12

GSM ArchitectureAuthentication Centre (AUC)

• e or s respons e or po c ng ac onsin the network.

• This has all the data required to protect thenetwork against false subscribers and to protectthe calls of regular subscribers.

• There are two major keys in the GSM standards:the encr tion of communication between mobile

users, and the authentication of the users.• The encryption keys are held in the mobile

equipment and the AUC and the information isprotected against unauthorized access.

GSM Architecture

Equipment Identity Registers (EIR)• Each item of mobile equipment has its own personal

identification, which is denoted by a number- the

International Mobile Equipment Identity (IMEI).• The number is installed during the manufacturing of

the equipment and states its conformation to the

GSM standards. Whenever a call is made, the

network checks the identity number; if this number

is not found on the approval list of authorized

equipments, access is denied.

• The EIR contains this list of authorized numbers

and allows the IMEI to be verified.



13

GSM Architecture• Network Management System (NMS):

– The main task of the NMS is to ensure that

the running of the network is smooth. For this

purpose, it has four major tasks to perform

• Network Monitoring

• Network Development

• e wor easuremen s

• Fault Management

GSM Architecture

• GSM Interfaces

– There are three interface types:

1)Air interface

2)Abis interface



14

GSM ArchitectureAir Interface

•

every mobile system. The importance of this interface arises

from the fact that it is the only interface the mobile subscriber

is exposed to, and the quality of this interface is crucial for

the success of the mobile network.

• The GSM radio link uses the FDMA and TDMA technologies.

• The frequency bands for the GSM downlink and uplink signal

- - .

frequency band are divided into 124 pairs of frequencyduplex channels with 200kHz carrier spacing. Each cell site

has a fixed assignment of a certain number of carriers,

ranging from only one to usually not more than 15 channels.

The cell ranges in size from 1 to several km.

GSM Architecture

• The length of a GSM time frame in a frequency channel is 4.615 ms.

Which is divided into 8 time slots (bursts).

• The length of each time slot is 0.577 ms.

• The gross bit rate is about 270 kb/s (with a Gaussian minimum shift

keying GMSK)• The physical channel of the TDMA frames carry logical channels

that transport user data and signaling information.

Tailing Data Flag Training Flag Data Tailing Guard

3 57 bits 57 bits1 126 bits 38.25

bits

Time slot (156.25 bits or 0.577 ms.)



15

GSM Architecture935-960 MHz 124 channels (200 kHz) downlink

890-915 MHz 124 channels (200 kHz) uplink

time

GSM TDMA frame

1 2 3 4 5 6 7 8

546.5 μs

Tail

3 bits

tail3bits

User data57 bits

User data57 bits

Training26 bits

S1

S1

Guard

space

Guard

space

577 μs

GSM Architecture

– Abis Interface• bis

and the BSC. It is a PCM interface, i.e. it is definedby the 2Mb/s PCM link. Thus it has 32 channels of

64 kb/s each.• With 13Kb/s of air interface, each PCM channel

can multiplex 4 user.

– A Interface• The A interface is present between the MSC and

the BSC. This interface consists of one or morePCM links each having a capacity of 2Mb/s.



16

Multiple Access ConceptsFrequency Frequency

time

time

FrequencyCode

Code

FDMA TDMA

time

CodeCDMA

Frequency Division Multiple Access

Filter

Fre uenc

Channelsum

A

A

A B

A

Filter

er

Shift

B BB

Frequency

Shift



Time Devision Multiple AccessADC DACA

A

Channelt

ADC

DAC

Synchronization

A AB B

B

Code Division Multiple Access

∫

C1

Channel

C1

sum( ) ( ) ( )

( )

i j ij

ij

C t C dt ,

1 i j

1 i

τ = σ τ

<< ≠⎧σ τ = ⎨

= =

∫

C2

C2

∫

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