MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION … · 2015. 5. 25. · MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION (Autonomous) (ISO/IEC - 27001 - 2005 Certified) Summer – 14

MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION (Autonomous)

(ISO/IEC - 27001 - 2005 Certified)

Summer – 14 EXAMINATION

Subject Code: 12272 Model Answer

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Important Instructions to examiners:

1. The answers should be examined by key words and not as word-to-word as given in the

model answer scheme.

2. The model answer and the answer written by candidate may vary but the examiner may try

to assess the understanding level of the candidate.

3. The language errors such as grammatical, spelling errors should not be given more

Importance (Not applicable for subject English and Communication Skills.

4. While assessing figures, examiner may give credit for principal components indicated in the figure.

The figures drawn by candidate and model answer may vary. The examiner may give credit for

any equivalent figure drawn.

5. Credits may be given step wise for numerical problems. In some cases, the assumed constant

values may vary and there may be some difference in the candidate‟s answers and model answer.

6. In case of some questions credit may be given by judgement on part of examiner of relevant

answer based on candidate‟s understanding.

7. For programming language papers, credit may be given to any other program based on equivalent

concept.

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Q.1A.) Solve any three of the following

a) Describe the basic cellular system.

Answer:- (2M Diagram & 2 M Explanation)

OR

Fig. shows a cellular telephone system that includes all the basic components necessary for cellular

telephone communication.

The radio network is defined by a set of radio frequency transreceiver located within each of the

cells. The location of these radio frequency transreceiver are called base station

Base station: base station serves as central control for all users within that cell.

Mobile unit communicate directly with the base stations & the base stations communicate directly

with a mobile





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Telephone switching office (MTSO): The Switching center is one component which co-ordinates

the routing of calls in a large service area. An MTSO controls channel assignment, call processing,

call setup & call termination which includes signaling switching, supervision & allocating radio-

frequency channels. The MTSO provides a centralized administration & maintenance point for the

entire network & interfaces with the public telephone network over wire line voice trunks & data

links.

OR

{Note: Student can interpret block diagram in different way but it should consist basic blocks

marks should be given for that also.}

b) Draw the block diagram of mobile unit & explain each block

Answer:- . (2 M Diagram & 2 M Explanation)

Mobile unit:-

The RF selection contents the transmitter and receiver CKT including mixers local oscillators

or frequency. Synthesizers for channel selection. The receiver LNA and the transmitter power

ampere.

The base band selection contains the Vocoder with its A / D and D/ A converts plus a DSP

chip that handles many processing functions typically performed by analog ckt in older

synthesizers.

An embedded control handles all the digital control and signaling , hand offs and connection

and identification, operation that take place transparent to the subscriber.





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It also takes care of running the display and keyboard and all user functions such as number

storage, auto dialing and caller ID.

This has led to some interesting architectures especially, in the receiver section. Although

super heterodyne design is still used, several variations have emerged as dominant. These are

the down conversion and very low - IF designs.

c) Describe the functional Architecture of IMT-2000

Answer. (2M Diagram & 2M Explanation)

OR

Functional architecture of IMT – 2000 :-

IMT 2000 expected to support a number of different radio operating environments covering

indoor picocells with very high overall system capacity all the way through large outdoor

terrestrial cells and satellite.





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The broad classes of functions that need to be supported by an IMT -2000 system are shown in

the fig. above. It is seen that separation of call and collection controls functions and is

desirable for supporting multimedia and advanced services in IMT 2000 .

In this architecture the connection and call control function are integrated rather than separated.

It illustrates one possible assignment of functional entities to physical entities and identifies

relationship between these collection and function that need to be supported by the physical

interface specification.

d) Describe the GSM system architecture with neat block diagram.

Answer : (2 M Diagram & 2M Explanation)

z

Mobile Station

The mobile station (MS) consists of the mobile equipment (the terminal) and a smart card called

the Subscriber Identity Module (SIM).

The mobile equipment is uniquely identified by the International Mobile Equipment Identity

(IMEI). The SIM card contains the International Mobile Subscriber Identity (IMSI) used to

identify the subscriber to the system, a secret key for authentication, and other information.

Base Station Subsystem:

The Base Station Subsystem is composed of two parts:

1. The Base Transreceiver Station (BTS) and

2. The Base Station Controller (BSC).

These communicate across the standardized Ab is interface, allowing (as in the rest of the system)

operation between components made by different suppliers.

The Base Transreceiver Station houses the radio transreceivers that define a cell and handles the

radio-link protocols with the Mobile Station.

BTS

BTS

BTS

BTS

BTS

BTS

BSC

BSC HLR VLR AUC

OMC

MSC

PSTN

ISDN

DATA

NETWORKS

PUBLIC

NETWORK

NETWORK SWITCHING

SYSTEM BASE STATION

SUBSYSTEM

MS: MOBILE STATION BTS: BASE TRANSWERCIVER STATION

BSC: BASE STATION CONTROLLER MSC: MOBILE SWITCHING CENTER

VLR: VISITOR LOCATION REGISTER HLR: HOME LOCATION REGISTER

AUC: AUTHENTICATION CENTER OMC: OPERATIONAL & MAINTAINANCE

CENTER

PSTN: PUBLIC SWITCH TELEPHONE ISDN: INTEGRATED SERVICES DIGITAL

NETWORK NETWORK

MS

MS





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The Base Station Controller manages the radio resources for one or more BTSs. It handles radio-

channel setup, frequency hopping, and handovers, as described below. The BSC is the connection

between the mobile station and the Mobile service Switching Center (MSC).

Network Subsystem:

The central component of the Network Subsystem is the Mobile services Switching Center (MSC).

It acts like a normal switching node of the PSTN or ISDN, and additionally provides all the

functionality needed to handle a mobile subscriber, such as registration, authentication, location

updating, handovers, and call routing to a roaming subscriber.

These services are provided in conjunction with several functional entities, which together form

the Network Subsystem. The MSC provides the connection to the fixed networks (such as the

PSTN or ISDN). Signaling between functional entities in the Network Subsystem uses Signaling

System Number 7 (SS7), used for trunk signaling in ISDN and widely used in current public

networks.

The Home Location Register (HLR) and Visitor Location Register (VLR), together with the MSC,

provide the call-routing and roaming capabilities of GSM.

Q.1B.) Solve any one of the following. (6 Marks)

a) With the help of neat sketch explain the forward & reverse link channel structure used in IS-

95.

Answer : (1M Diagram & 2 M Explanation for forward & reverse link structure)

Forward channel is a communication channel used for transmission of information from BS to mobile

station.

Pilot channel: This channel allows a MS to acquire timing for forward CDMA channel. It provides a phase

reference for coherence demodulation. It provides each mobile with an answer for signal strength

comparison between BS for determining when to handoff.

Synchronization channel: The synchronization channel broadcasts synchronization message to the MS.

The sync channel message parameters are System Identification (SID) and Network Identification (NID)





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Paging Channel: The paging channel is used to send control information and paging messages from BS to

the mobile and paging messages from BS to the mobile.

Forward Traffic channel: Information on the forward traffic channel includes the primary traffic (voice

and data) secondary traffic (data) and signaling.

Reverse channel is a communication channel used for transmission of information from MS to base

station

.

Access channel: On access channel mobile users communicate short messages such as information

registration, call origination, and responses to pages, or providing other data to cell site. When mobile user

places a call, it uses the access channel to inform the serving base station.

Reverse Traffic channel: This traffic channel carries the user speech or data. It is similar to the forward

traffic channel and is intended to transfer dedicated user data. The traffic channels in reverse channel are

unique to each mobile user.

b) Draw & describe the transmitter system in cellular communication with block diagram.

Answer:- (3 M Diagram & 3 M Explanation).





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It is a Low-Power FM unit operating in Frequency range of 825 MHz. Channel 1 is 825.03 MHz,

Channel 2 is 825.06 MHz & So on.

The carrier furnished by frequency synthesizer is phase-modulated by the voice signal.

The modulator output is translated up to the final transmitter frequency by a mixer whose second

input also comes from frequency synthesizer.

The mixer output is fed to class c & or class E power ampere stages where output signal is

developed. The final ampere stage is designed to supply about 600 mw to the antenna.

The APC ckt can introduce power attenuation in steps of 4db to 28db.

This s/g is used in APC ckt & is Transmitted back to the cell site, permitting the MTSO to know the

current power level.

The transmitter output is fed to a duplexer ckt or isolator that allows the transmitter & receiver to

share the same antenna. Since cellular telephone units use full duplex operation, the transmitter &

receiver operates simultaneously.

The duplexer consists of two very sharp BPF, one for the transmitter & one for the receiver. The

transmitter output passes through this filter to the antenna.

Q.2) Solve any four of the following.

a) Draw frequency reuse pattern with cluster size 7 & 12.

Answer: - (2 marks for each pattern)

For cluster size 7:





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For cluster size 12:

b) List various features & services of IS-95.

Answer:- Features & services of IS-95 – (Any Eight 4M)

1. Diversity

2. Power control

3. Soft handoff

4. IS-95 system capacity

5. Soft capacity

6. Quality of service

7. Economics

8. Variable Rate Vocoder Offering high speed coding and reducing background noise and system

9. Interference based on the detection of the voice activity.

10. Coding Technique for Enhancing the privacy and security.

11. Roaming

c) Describe the mobile call Terminations

Answer:- . ( 2M Diagram & 2M Explanation)





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Mobile call termination:

1. The PSTN user dials the MSISDN of the called user in GSM.

2. The LE routes the call to the GMSC of the called GSM user.

3. The GMSC uses the dialed MSISDN to determine the serving HLR for the GSM user and

interrogates it to obtain the required routing number.

4. The HLR requests the current serving VLR for the called MS for a MSRN(MS roaming number)

so that the call can be routed to the correct MSC.

5. The HLR passes the MSRN to the GMSC.

6. Using the MSRN, the GMSC routes the call to the serving MSC.

7. The MSC interrogates the VLR for the current location area identity (LAI) for the MS.

8. The VLR provides the current location for the MS.

9. The MSC pages MS via the appropriate BSS. The MS responds to the page and sets up the

necessary signaling links.

10. When the BSS has established the necessary radio links, the MSC is informed and the call is

delivered to the MS.

12. When the MS Answer the call, the connection is completed to the calling PSTN user. The

VLR passes the MSRN to the HLR

d) Draw & describe the network architecture of UMTS

Answer:- (2 marks Diagram & 2 marks Explanation)

The UMTS is a system that is capable of providing a variety of mobile services to a wide range of

global mobile communication standards.

To handle a mixed range of traffic, a mixed cell layout, which would consist of macrocells

overlaid on microcells & picocells is one of the plans being considered.

This type of network distributes the traffic with the local traffic operating on the microcells &

picocell, while the highly mobile traffic is operated on macrocell, thus reducing the number of

handoffs required for fast moving traffic.





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It is observed from the fig. that the macro cells cover the spots not covered by other cells & also

provide redundancy in certain areas.

Thus macro cells will also be able to avoid the failures of the overlapped cells.

e) Define the following terms w.r.t. mobile communication.

Base station

Forward Channel

Control Channel

Voice Channel

Answer:- (1M each)

Base station: - A fixed station in a mobile radio system used for radio communication with

stations. Base stations are located at the center or on the edge of a coverage region & consist of

radio channel & Transmitter and Receiver antennas mounted on a tower.

Forward Channel: - Radio channels used for Transmission of information from the BASE

STATION to the MOBILE.

Control Channel :- Radio channels used for Transmission of call setup, call request, call

Initiation & other beacon or control purpose.

Voice Channel: Radio channels used for Transmission & reception of voice messages.





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Q3 Attempt any four. ( 16 Marks)

a) Describe the near end far end interference in cellular system

Answer:

If motor vehicle in a given cell is moving, then some mobile phone units are close to the

cell site and some are not. The close in mobile phone unit has a strong signal which causes

adjacent-channel interference

In this situation, near end – far end interference can occur only at the reception point in the

cell site

If a separation of five channel bandwidth 95B) is needed for two adjacent channels in a

cell in order to avoid the near end – far end interference, it is then implied that a minimum

separation of 5B is required between each adjacent channel used with one cell

The adjacent channel interference can also occur between two systems in a duopoly market

system

In this situation, adjacent channel interference can occur at both the cell site and the mobile

phone unit

For instance, mobile phone unit A can be located at the boundary of its own home cell A in

the system A but very close to cell B of system B

The other situation would occur if mobile phone unit B was at the boundary of cell B of

system B but very close to cell A of system A.

The same interference will be introduced at cell B and mobile unit B

The two causes of near end – far end interference are as below

Interference caused on the set up channels

Interference caused on the voice channels

The adjacent channel interference can be minimized through careful filtering and channel

assignments

Since each cell is given only a fraction of the available channels a cell need not be assigned

channels which are all adjacent in frequency

By keeping the frequency separation between each channel in a given cell as large as

possible the adjacent channel interference may be reduced considerably

Some channel of allocation schemes also prevent a secondary source of adjacent channel

interference by avoiding the use of adjacent channels in neighboring cell sites

In practice, the base station receivers are preceded by high Q cavity filter in order to reject

adjacent channel interference

The adjacent channel interference can be reduced by the frequency assignment





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b) Describe the WLL technology and also write its application

Answer: (3M diagram , 3 M explanation)

WLL stands for Wireless Local Loop. Microwave wireless links can be used to create a wireless

local loop such as shown in figure below.

Local Loop is a network that resides between the central office (CO) and the individual

homes and business in close proximity to the central office (CO) as shown in figure above.

In most developed countries, copper or optical fiber cable already has been installed to

residence and business.

One more advantage of WLL is that we have to pay only once for that wireless equipment,

after there is no additional costs involved.

System WLL is based on Cellular, satellite, microcellular

The WLL can greatly improve the telecommunication facilities and services in an

inexpensive way.





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OR 3 marks Wi Wireless Access Network Unit (WANU): Interface between underlying telephone network and

wireless link. It consists of Base Transceiver Station (BTS), Radio Controller (RPCU), Access

Manager (AM), Home Location Register (HLR)

Wireless Access Subscriber Unit (WASU): Located at subscriber side. Translates wireless link into

a traditional telephone connection

c) Describe the microcell zone concept

Answer: 2 Marks--- Diagram

2 Marks--- Explanation

The problem associated with the sectoring is the number of handoffs. This puts additional

load on the switching and control link elements of the mobile system.

A solution to this problem is based on microcell concept for seven cell reuse.





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In this scheme, all the three or more zone sites represented as Tx/Rx are connected to the

same base station and share the same radio equipment.

The transmission media used for connecting the zones to the base station are coaxial cable,

fiber optics cable or a microwave link.

So each cell consists of a base station and multiple zones.

A mobile travelling within a cell is served by the zone that has the strongest signal of all.

As shown in figure, the antennas in zones are placed at the outer edge of the cell and any

base station channel can be assigned to any zone by the base station.

As a mobile travels from one zone to the other within a cell, it uses the same channel. This

will avoid handoff. The base station will just switch the channel to the appropriate zone

site.

Thus a given channel is being used only in a particular zone in which the mobile is

travelling. So the base station radiation is localized. This will reduce interference.

The channels are distributed in space and time by all zones and are reused in the co channel

cells.

The microcell zone concept is very useful along highways or in the busy areas

d) List the basic features and coding methods in CDMA

Answer:- The various types of codes and coding methods used in CDMA system are as under:

Auto correlation codes- a) Barker code b) Pseudo- noise codes

Orthogonal codes

Walsh codes

Scrambling codes

Channelization codes

Carrier modulation codes

Features: (any 3 feature) 3 marks

It is wide band DS-CDMA system

W-CDMA assures backward compatibility with the 2G GSM.

Packet data rate-2.048 Mbps

Channel Bandwidth- 5MHz

Provides high capacity upgrade path for GSM

Frame structure- 16 slots per frame

Network structure and bit level packaging of GSM data is retained

Computers, entertainment devices, and telephone may all share same wireless network and

be connected to internet anytime anywhere.

Each channel will be able to support between 100 to 350 voice channels.

Uses Direct Sequence Spread Spectrum (DSSS) with chip rate of 16Mcps.

Provides Videoconferencing and Virtual Home Entertainment (VHE)





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e) Write a short note on the evolution of radio mobile communications

Answer:-

Mobile wireless (or radio) communication has started after of electromagnetic (or radio)

waves by Hertz

Mobile radio communication systems using simplex channel introduced in 1920 for

emergency services in USA

First public mobile radio system in USA introduced in 1946

The cellular concept was developed by ATT in 1947 and commercial tests were done in

1962

In 1970, ATT proposed AMPS.

In 1979 worlds first cellular system was implemented by Nippon Telephone. The analog

cellular mobile systems fall in the category of 1st generation mobile system

Besides frequency reuse, digital signal processing, integrated circuits, increased battery life

lead to exponential growth in mobile communication.

The first digital system cellular system was introduced in 1990 by ETSI for GSM. This was

considered to be second generation mobile comms

The 3rd generation digital cellular system called PDC was developed by Japan for

commercial uses

In late 1991, DSDC system hardware was installed in USA, it improved the capacity by 3

times of that provide by AMPS

A cellular system based on CDMA was developed by Qualcomm and standardized by TIA.

With the rapidly increasing penetration of laptop computers which are primarily used by

mobile users to access internet services. Mobile IP allows IP nodes to change physical

location without having to change IP address there by offering nomadicity to internet users

IMT-2000 standard is being developed to set stage for 3rd generation mobile

communication system. It will consolidate different wireless environment and will also

ensure global mobility in terms of global seamless roaming and delivery of services

ETSI has also developed 3rd generation mobile communication system call UMTS which

belongs to IMT-2000 system

Q-4 Attempt any three

a) Describe the messages and call processing in GSM system

Answer: 1 mark—Diagram





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1 mark explanation

Mobile call origination in GSM

The MS sends the dialed number indicating service requested to the MSC(via BSS)

The MSC checks from the VLR if the MS is allowed the requested service. If so, MSC asks

BSS to allocate necessary resources for the call.

If the call is allowed, the MSC routes the call to GMSC.

The GMSC routes the call to the local exchange of called user.

The LE alerts (applies ringing) the called terminal.

Answer back (ring back tone) from the called terminal to LE.

Answer back signal is routed back to the MS through the serving MSC which also

completes the speech path to the MS.

OR

1 mark—Diagram

1 mark—Explanation

Mobile call termination:

The PSTN user dials the MSISDN of the called user in GSM.

The LE routes the call to the GMSC of the called GSM user.

The GMSC uses the dialed MSISDN to determine the serving HLR for the GSM user and

interrogates it to obtain the required routing number.

The HLR requests the current serving VLR for the called MS for a MSRN (MS roaming

number) so that the call can be routed to the correct MSC.

The VLR passes the MSRN to the HLR.

The HLR passes the MSRN to the GMSC.

Using the MSRN, the GMSC routes the call to the serving MSC.





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The MSC interrogates the VLR for the current location area identity (LAI) for the MS.

The VLR provides the current location for the MS.

The MSC pages MS via the appropriate BSS. The MS responds to the page and sets up the

necessary signaling links.

When the BSS has established the necessary radio links, the MSC is informed an the call is

delivered to the MS.

When the MS answers the call, the connection is completed to the calling PSTN user.

Message Processing 2M OR any other correct explanation should be considered

1. Types: The types of messages to be transmitted over the reverse control channel

(RCCH) are:

Page response message: When the mobile station receives a page from the land station, the

mobile station responds back.

Origination message: The mobile station originates the call.

Order confirmation message: The mobile station responds to the order from the land

station.

Order message: The mobile station orders the tasks which should be performed by the land

station and the mobile transmission switching office (MTSO).

2. Structure: All messages contain the following:

An application message header

Mandatory fixed parameters

Mandatory variable parameters

Remaining length

Optical variable parameters

b) Describe the architecture of SS

Answer:-

The message transfer part (MTP) provides OSI level protocol model as level-1 data service,

level-2 link service and level-3 network service

The full level-3 service is provided by the signaling connection control part (SCCP)

The SCCP provides an enhanced addressing capability that may be considered as level 3+

or close to level-4

The layer 4-6 in the OSI model don‟t exist in SS7 protocol model

The transaction capability application part (TCAP) level and operations maintenance and

administration (OMAP) part level are considered the same as the Application level-7 in the

OSI

The application service element ASE is at the same level as the OMAP

The TCAP includes protocol and services to perform remote operations

The primary use of TCAP in these networks is for invoicing remote procedures in

supporting IN service like, 800 services

The OMAP provides the application protocols and procedures to monitor coordinate and

control all the network resources which make communication based on SS7 possible





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The ASE is for the MTP routing verification test (MRVT) which uses the connectionless

services of TCAP

The MRVT is an important function on OMAP

c) How and why is the variable spread factor used in CDMA 2000

Answer:-

In case of CDMA 2000 the spread factor can vary from 4 to 256 depending upon the data

rates.

The use of interleaving and variable spread factor enables support of the data rates up to

386kbps

When high data rate signals are to be transmitted then multi carrier transmission can be

used

We can use N carriers where N=1, 3, 6, 9 or 12 in CDMA 2000. Similarly chipping rates of

Nx1.2288 M-chips-per-sec can be used

In CDMA 2000 there are three carriers of 1.25 MHz each for N=3 and all carriers have a

separate code for each channel

Any relevant answer should be given full marks

d) What is the necessity of logical channel in GSM system

Answer:-

In practice, a multimode terminal used by a third generation (3G) mobile communication

system network will have to scan for suitable frequency band or channel, identify

application radio and standard and select from among the set or available services





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If it develops at a very large number of frequency bands need to be scanned and the many

standards need to be searched registering such a roaming multimode terminal by means of

systematic scanning procedure will become very inefficient, tending to degrade quality of

service for the users perspective

This problem can be alleviated by using common physical or logical broadcast channel

called the global radio control channel

Therefore there is a necessity of logical channel in GSM system to scan a single frequency

or a small range of frequency and thereby find the required information on available

network or standards and services

Q.5. Attempt any two: 16 Marks

a) Describe how the improving coverage and capacity in cellular system and also list the

techniques for improving the capacity of cellular system.

Answer:

(Note: If student draw the diagram of Cell splitting, Cell sectoring, microcell zone concept,

frequency reuse then 2 M for diagram 2 M for explanation should be given)

Description:

Cell splitting is the process of subdividing congested cell into smaller cells, each with its own

base station and a corresponding reduction in antenna height and transmitter power.

Cell splitting increases capacity of a cellular system since its increases the number of times

that channels are reused.

Cell sectoring increases SIR using directional antennas, then capacity improvement is

achieved by reducing the number of cells in a cluster, thus increasing frequency reuse.

Often wireless operator needs to provide dedicated coverage for hard-to-reach areas. Such as

within buildings, or in valleys or tunnels. Radio transmitters, known as ―repeaters‖ are often

used to provide such range (coverage) extension capabilities.

In microcell zone concept each of three (or possibly more) zone sites are connected to a single

base station and share the same radio equipment. Decreased co-channel interference improves

the signal quality and also leads to increase in capacity without the degradation in trunking

efficiency caused by sectoring.

By limiting the coverage area to within the boundaries of a cell, the same group of channels

may be used to cover different cells that are separated from one another by distance large

enough to keep interference levels within tolerable limits and capacity of system can be

increases is called a frequency reuse or frequency planning.

Techniques for improving capacity:

Cell splitting

Cell sectoring

Microcell-zone concept





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Frequency Reuse

b) Write a note on following components:

a) Mobile station

b) Forward channel

c) Base Station controller

And also state the advantages of cellular mobile services.

Answer :

Mobile Station: (2 Marks)

A Station in cellular radio service intended for use while in motion at unspecified locations.

Mobile stations may be handheld personal units (portable) or installed in vehicles (mobiles). A MS

comprises of single antenna, transceiver, and microprocessor- based control circuit. Because

cellular system is full duplex, the transmitter and receiver must operate with single antenna.

Forward channel: (2 Marks)

A radio channel used for transmission of information from the base station to mobile is called

forward channel. The forward voice channel can be further divided in to Forward Voice Channel

(FVC) which is used for voice transmission from base station to mobile, and Forward Control

Channel (FCC) which is responsible for initiating mobile calls, and service requests, and are

monitored by mobile when they do not have a call in progress.

Base Station Controller (BSC): (2 Marks)

The base station controller manages each of the radio channels at each cell-site, turns the radio

transmitter and receiver ON and OFF, transfers‟ data on to the control and voice channels,

monitors calls and performs built-in diagnostic tests on the cell-site equipment. The BSC operates

under the control of the central switching center MSC or MTSO.

Advantages of cellular mobile services: (2 Marks)

Instant Communications- “Coast to Coast in Under a Second”.

Solves many interoperability problems with first responders.

Bypasses the PSTN.

Higher voice compression= less blocking.

Priority Connect available.

High and variable data rate.

On the air privacy

Subscriber Identity Module (SIM)

c) Draw the block diagram and explain each block and also write the list of various types of SS7

services.

Note: Any of the block diagram or Protocol architecture should be given marks





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Answer:

The SS7 signaling protocol is widely used for Common Channel Signaling (CCS) between

interconnected networks.

Block Diagram: (3 Marks)

Explanation of each block: (3 Marks)

An SS7 network is composed of service switching points (SSPs), signaling transfer points

(STPs), and service control points (SCPs).

Service Switching Point (SSP): The SSP gathers the analog signaling information from the local

line in the network (end point) and converts the information into an SS7 message. These messages

are transferred into the SS7 network to STPs.

Signaling Transfer Points (STPs): The STP transfers the packet closer to its destination. When

special processing of the message is required (such as rerouting a call to a call forwarding

number), the STP routes the message to a SCP.

Service Control Points (SCPs): The SCP is a database that can use the incoming message to

determine other numbers and features that are associated with this particular call.

Signaling Connection Control Part (SCCP) translation function: This is a process in the SS7

system that uses a routing tables to convert an address (usually a telephone number) into the actual

destination address (forwarding telephone number) or into the address of a service control point

(database) that contains the customer data needed to process a call.

OR





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Protocol Architecture: (3 Marks)

Explanation of protocol architecture: (3 Marks)

Network Service Part of SS7: The NSP provides ISDN with a highly reliable and efficient means

of exchanging traffic using connectionless services.

a) Signaling data link functions (MTP Level 1): This level provide an interface to the actual

physical channel over which communication takes place.

b) Signaling link function (MTP Level 2): It provides a reliable link for the transfer of traffic

between two directly connected signaling points.

c) Signaling Network Function (MTP Level 3): Provides procedure that transfer message

between signaling nodes.

d) Signaling Connection Control Part (SCCP): The SCCP provides enhancement to the

addressing capabilities provided by the MTP. SCCP also provides the ability to address global

title messages, such as 800 numbers or non-billed numbers.

SS7 User Part: SS7 user part provides call control and management functions and call setup

capabilities to the network.

a) Integrated Service Digital Network User Part (ISUP): The ISUP provides the signaling

functions for carrier and supplementary services for voice, data and video in ISDN

environment. ISUP uses the MTP for transfer of messages between different exchanges.





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b) Transaction Capabilities Application Part (TCAP): The TCAP part in SS7 refers to the

application layer which invokes the services of the SCCP and the MTP in a hierarchical

format.

c) Operation Maintenance and Administration Part (OMAP): The OMAP functions include

monitoring, co-ordination and control function to ensure that trouble free communications are

possible.

Various types of SS7 services: (any two) (2 Marks)

Touch star

800 services

Alternate billing services and Line Information Database (LIDB)

Q.6 Attempt any two: 16 Marks

a) Draw the schematic diagram of a basic cellular telephone system and describe it.

Answer:

A cellular telephone system provides a wire-less connection to the PSTN user for any user location

within the radio range of the system.

Schematic Diagram: (4 Marks)

Description: (4 Marks)

Figure above shows a basic cellular system which consists of

Mobile Station (MS)

Base Station (BS), and

Mobile Switching Centre (MSC) OR Mobile Telephone Switching Office (MTSO)





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1) Mobile Station (MS): The mobile station contains a transceiver, an antenna, and control circuitry

and may be mounted in a vehicle or used as a portable hand-held unit.

2) Base Station (BS):

The base stations consist of several transmitter and receiver which simultaneously handle

full duplex communication and generally have towers which support several transmitting

frequency and receiving antennas.

The BS serves as a bridge between all mobile users and connects simultaneous mobile calls

via telephone lines or microwave links to the MSC.

3) Mobile Switching Centre (MSC):

The MSC co-ordinates the activities of all the base stations and connects the entire cellular

system to the PSTN.

A typical MSC handles 100,000 cellular subscribers and 5,000 simultaneous conversations

at a time, and accommodates all billing and system maintenance functions as well.

Communication between the BS and mobiles is defined by a standard Common Air

Interface (CAI) that specifies four different channels.

4) Forward Voice Channel (FVC): This channel is used for voice transmission from the BS to

mobile.

5) Reverse Voice Channel (RVC): This channel is used for voice transmission from mobile to BS.

6) Forward Control Channel (FCC) and Reverse Control Channel (RCC):

These channels are responsible for initiating mobile calls. Control channels are often called

“setup channels” because they are only involved in setting up a call and moving it to an

unused voice channel.

Control channels transmits and receives data messages that carry call initiation and service

requests, and are monitored by mobiles when they do not have a call in progress.

b) Describe the Co-channel interference and system capacity in mobile communication.

Answer:

Co-channel Interference:

Diagram (any 1):

(2 marks)

OR





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Explanation: (3 Marks)

Frequency reuse implies that in a given coverage areas there are several cells that use the same set

of frequency.

These cells are called co-channel cells, and the interference between signals from these cells is

called co-channel interference.

Unlike thermal noise which can be overcome by increasing the signal-to-noise ratio (SNR), co-

channel interference cannot be combated by simply increasing the carrier power of transmitter.

This is because an increase in carrier transmits power increase the interference from neighboring

co-channel cells.

To reduce co-channel interference, co-channel cells must be physically separated by a minimum

distance to provide sufficient isolation due to propagation.

When the size of each cell is approximately the same and the base stations transmit the same

power, the co-channel interference ratio is independent of transmitted power and becomes a

function of the radius of the cell (R) and the distance between centers of the nearest co-channel

cells (D).

By increasing the ratio D/R, the spatial separation between co-channel cells relative to the

coverage distance of a cell is increased.

Thus interference is reduced from improved isolation of RF energy from the co-channel cell.

Capacity of system: (3 Marks)

The parameter Q is called the co-channel reuse ratio, is related with cluster size (N).

For hexagonal geometry;





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A small value of „Q‟ provides larger capacity since the cluster size „N‟ is small.

Whereas a large value of „Q‟ improves the transmission quality, due to a smaller level of co-

channel interference.

A trade-off must be made between these two objectives in actual cellular design.

c)List various features and services of IS-95 and also write the various services offered by a GSM

system.

Answer:

Features of IS-95: (any three) (3 Marks)

Diversity

Power control

Soft hand-off

A 3-finger RAKE receiver is used in IS-95 to improve reception at the BS and MS.

Many users of a CDMA system share the same frequency. Either TDD or FDD is used.

Channel data rate is very high in IS-96 CDMA system.

Services of IS-95: (any two) (2 Marks)

Short Message Services (SMS)

Slotted paging

Over the air activation

Call services

Data services

Services offered by GSM system: (any three) (3 Marks)

1) Telephone Services:

Standard mobile telephone

Mobile-originated

Base-originated traffic.

emergency calling

Fax

Videotext

Tele text,

SMS

MMS.

2) Supplementary ISDN services:

Call diversion

Caller line ID

Closed user group

Call barring

Call waiting





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Call hold

Connected line ID

Multiparty (Teleconferencing)

Call charge advice

This service also include the Short Messaging Service (SMS) which allow GSM subscriber and

BS to transmit alphanumeric pages of limited length (160 -7 ASCII characters) while

simultaneously carrying normal voice traffic.

Documents

MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION … · 2015. 5. 25. · MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION (Autonomous) (ISO/IEC - 27001 - 2005 Certified) Summer – 14