1

Vidyalankar T.Y. Diploma : Sem. VI

[EJ/ET/EN/EX] Mobile Communication

Time : 3 Hrs.] Prelim Question Paper Solution [Marks : 100

Q.1(a) Attempt any THREE of the following : [12]Q.1(a) (i) State four ways to improve capacity and coverage in cellular system. [4](A) (If student draw the diagram of Cell splitting, Cell sectoring, microcell zone concept, frequency

reuse then 2 M for diagram 2 M for diagram 2 M for Note 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 hardtoreach 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 cochannel 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 Frequency Reuse Q.1(a) (ii) State specification of IMT2000 [4](A) Specification of IMT2000 [Any 8 Features - 4 Marks] It is more robust for multipath delays and provides higher immunity towards frequency

selective fading. It has very high channel data rates. It gives signal of higher voice and data quality and also small bit error rates. It has a very high channel bandwidth. It has a common worldwide spectrum band. It can operate in multiple ratio environments such as cellular, cordless, satellite, LAN etc. It has a wide range of telecommunication service such as voice, data, multimedia, internet

etc. It provides global seamless connectivity to the mobile system. It has a improved security and enhanced performance. It has global coverage due to integrations of satellite and terrestrial system.

Vidyala

nkar

Vidyalankar : T.Y. Diploma MC

2

Q.1(a) (iii) Write short note on evolution of radio mobile communication. [4](A) [4 mark] 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 communication. 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.1(a) (iv) State examples of wireless communication system and explain any one in detail

with labelled block diagram. [4]

(A) Examples of wireless communication system are: [1 mark] 1) Paging System 2) Cordless Telephone System 3) Cellular System [2 marks] Paging System

Vidyala

nkar

Prelim Question Paper Solution

3

[1 mark] Pager is a Simplex Communication Device. Paging Systems are communication systems that send messages to a subscriber. Message can be numeric or alphanumeric. Paging Systems are used to notify a subscriber of the need to call a particular telephone

number or to travel to a location to receive further instructions. In modern paging systems, news headlines, faxes can also be sent. A message is sent to a paging subscriber via the paging system access number with a

telephone keypad or modem. The issued message is called a Page. The paging system then transmits the page throughout the service area using base stations

which broadcast the page on a radio carrier. The coverage area of a simple paging system ranges from 2 to 5 km while a wide paging

system can have a worldwide coverage area. Whenever a sender wants to send a message to a receiver he dials the 10 digit pager number

of receiver through his telephone. Then this call is accepted by the operator present in the paging control center to whom the

receiver pager number and the message to be sent has to be sent. Then the operator will broadcast the message and the receiver paging number to all the

paging terminals or the base stations. Then a particular base station under the area where the receiver is present will transmit the

message to the receiver pager. Then the receiver’s pager device will receive all messages and will verify whether the sender

number is stored in its memory or not. If it is stored then the pager device will give beep which indicates the receiver that a message

is sent by sender to his pager and the message will be displayed in the LCD. Cordless Telephone System 2 marks]

[1 mark] Cordless Telephone Systems are full duplex communication systems that use radio to connect a portable handset to a dedicated base station, which is also connected to a dedicated telephone line with a specific telephone number on PSTN. The fixed port of a cordless telephone is nothing but the base unit on which cordless handset

is placed, is connected to a telephone line and an adapter to produce a dc supply for various electronic circuits inside the base unit.

The communication between the base unit and the handset is wireless and the range is limited to 50 meters.

In the base unit all call processing circuits like amplifiers and also ring circuit is present. In addition a transceiver is also present which is used for communication with the handset.

In handset also the transceiver along with an antenna, amplifier, microphone and loud speaker are present.

Vidyala

nkar

Vidyalankar : T.Y. Diploma MC

4

1st generation cordless telephone systems could cover only distance of a few ten meters(approximately 50m)and can be operated solely as extension telephones to a transceiver connected to a subscriber line on the PSTN and are primarily for in-home use.

2nd generation cordless telephone systems could cover distance of a few hundred meters which allows subscribers to use their handsets at many outdoor locations within urban centers.

Cordless telephone systems provide the user with limited range and mobility, as it is not possible to maintain a call if the user travels outside the range of the base station.

Cellular System The basic systems present in the cellular system are: Base Station: A fixed station in a mobile radio system used for radio communication with mobile stations.

Base stations are located at the center or on the edge of a coverage region and consist of radio channels and transmitter and receiver antennas mounted on a tower.

Control Channel: Radio channel used for transmission of call setup, call request, call initiation and other beacon or control purposes.

Forward Channel: Radio channel used for transmission of information from the base station to the mobile.

Reverse Channel: Radio channel used for transmission of information from mobile to the base station.

Mobile Station: A station in the cellular radio service intended for use while in motion at unspecified locations. Mobile stations may be hand-held personal units (portable) or installed in vehicles (mobiles).

Mobile Switching Center: Switching Center which co-ordinates the routing of calls in a large service area. In a cellular radio system, MSC connects the cellular base station and the mobiles to the PSTN. An MSO is also called as Mobile Telephone Switching Office (MTSO).

Transceiver: A device capable of simultaneously transmitting and receiving radio signal Forward Voice Channel: Radio channel used for voice transmission from the base station

to the mobile. Reverse Voice Channel: Radio channel used for voice transmission from mobile to the

base station.

Vidyala

nkar

Prelim Question Paper Solution

5

Q.1 (b)Attempt any ONE of the following : [6]Q.1 (b)(i) Draw GSM architecture and write function of each block [6](A) [Diagram - 3 marks, subsystem name - 1 mark and function of OMC - 2 mark] The GSM Architecture Consists of following subsystems :

1. Mobile Station Mobile Equipment SIM 2. Base Station Subsystem Base Transceiver Station Base Station Controller 3. Network and Switching Subsystem Mobile Switching Center Home Location Register Visitor Location Register Authentication Center Operation & Maintenance Center Equipment Identity Register 4. Operation Support Subsystem Public Switched Telephone Network Integrated Services Digital Network Function of Operation maintenance center (OMC) Network operation and maintenance functions, subscription, management including

charging and billing and also mobile equipment management. The OMC also has provision for adjusting all base station parameter and billing

procedure as well as providing system operators with the ability to determine the performance and integrity of all equipment’s in the system.

Vidyala

nkar

Vidyalankar : T.Y. Diploma MC

6

Q.1 (b)(ii) Explain process of mobile originated call in GSM system. [6](A) [Diagram and Description – 3 marks each]

Mobile call origination in GSM 1) The MS sends the dialed number indicating service requested to the MSC (via BSS) 2) 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.

3) If the call is allowed, the MSC routes the call to GMSC. 4) The GMSC routes the call to the local exchange of called user. 5) The LE alerts (applies ringing) the called terminal. 6) Answer back (ring back tone) from the called terminal to LE. 7) Answer back signal is routed back to the MS through the serving MSC which also

completes the speech path to the MS. Q.2 Attempt any Four [16]Q.2 (i) Compare cell sectoring with cell splitting. [4](A) 4 Marks for correct four comparison points

Cell sectoring Cell splitting The technique used for decreasing the co-channel interference & improving the capacity of a cellular system by using directional antenna & frequency reuse concept is called sectoring.

It is the process of subdividing a congested cell into smaller cell with its own base station having the corresponding reduction in the antenna heights & the transmitted power.

In cell sectoring the cell is normally partitioned into three 120 degree sectors or 60 degree sector.

There are two cell splitting techniques, 1. Permanent splitting 2. Dynamic splitting

Improves the signal to interference ratio & hence reduces co-channel interference

This technique utilizes the allocated spectrum efficiency in real time. In situations such as traffic jams, the ideal small cell sites may be rendered operative in order to increase the cell’s traffic capacity

Vidyala

nkar

Prelim Question Paper Solution

7

Q.2 (ii) State specification of Bluetooth [4](A) Any four specifications 1M each 1) RF spectrum allocation:2.4GHZ(Unlicensed ISM Band) 2) Number of RF channels:79 3) Channel Bandwidth:1MHZ 4) Frequency hop rate:1600 hops/sec 5) Modulation scheme:GFSK 6) Symbol transmission rate:1 Msps Q.2 (iii) Compare 3G CDMA 2000 with 3 G TDSCDMA [4](A) 4 Marks for correct four comparison points

Parameter 3G-TD-SCDMA 3G CDMA Spectrum utilization

Less spectrum utilization, 5ms frame is used & divided in to seven time slot and assigned to user

High spectrum utilization because it uses three adjacent 1.25MHz radio channels & operated simultaneously in parallel.

Bandwidth High, 1.6 MHz Low, 1.25MHz Data Rate Up to 384 kbps of packet data rate Up to 144 kbps for voice & data users.

Antenna Used

Smart antenna

Simple antenna

Q.2 (iv) Distinguish between WCDMA and IS95 [4](A) 4 Marks for correct four points of comparison

Parameter W-CDMA IS-95 1) Channel Bandwidth 5MHZ 1.25 MHZ 2) chip rate 3.84 Mcps 1.2288Mcps 3) Data rate Up to 2 Mbps Up to 9.6 kbps 4) frame size 10 ms 20 ms 5) Spreading factor Up to 512 64 6) Number of channel/terminal Variable 1 7) Downlink/uplink sharing FDD/TDD FDD 8) Downlink modulation QPSK QPSK 9) Uplink modulation QPSK OQPSK/Orthogonal 10)Traffic channels/RF Channel Depends upon data rate Up to 63 in theory

Vidyala

nkar

Vidyalankar : T.Y. Diploma MC

8

Q.2 (v) Give any four applications of MANET [4](A) Any four applications 1M Each 1) Personal area networking formed with cellphones, laptops, notebooks,PDA’S 2) Education sector such as virtual classrooms, conferences, seminars 3) Sensor networks for homes, environmental applications, wearable computing 4) Civilian environments like meeting rooms, sports stadiums, hospitals 5) Military environments in battlefields by soldiers in tanks/planes 6) Emergency operations such as search –and-rescue in case of natural disasters. Q.2 (vi) Determine [4] 1) The channel capacity for a cellular telephone are comprised of 7 macro cells

with 16 channels per cell 2) Channel capacity if each macro cell is further spilt in to 4

minicells. 3) Channel capacity if each minicell is further split into 4 microcells. (A) S = Total duplex channels K = Number of channels per cells N = Number of cells M = Number of clusters Capacity = kMN 1. N = 7 k = 16 C = kMN = 16 x 1 x 7 = 112 2 N = 7 x 4 = 28, k = 16 C = 16 x 1 x 7 x 4 = 112 x 4 = 448 3 N = 28 x 4, k = 16 C = 16 x 7 x 4 x 4 = 448 x 4 = 1792 Q.3 Attempt any Four [16]Q.3 (i) Draw block diagram of cellular receive and write the function of each block (A)

(Receiver diagram – 2 Marks, principle of operation – 2 Marks, It is a dual conversion superheterodyne receiver Signal received by the antenna is isolated from the o/p stage of the transmitter with the help of a device called duplexer. The duplexer connect the received signal only to cellular receiver i/p. The duplexer o/p goes to the RF amplifier which boosts the level of i/p signal to a sufficient value & applies it to the first mixer.

Vidyala

nkar

Prelim Question Paper Solution

9

The second input to mixer 1 is the local oscillator 1 signal obtained from frequency synthesizer. The receiver range is 870.03 to 889.98MHz. The first mixer will convert the incoming signal to produce the first IF which is equal to 82.2 MHz. This signal passes through first IF amplifier where it is amplified & applied to 2nd mixer. The local oscillator for the 2nd mixer is crystal oscillator. 2nd down conversion takes place at the 2nd mixer. 2nd IF of 10.7 MHz is produced. Signal is amplified by 2nd IF amplifier & demodulated by FM demodulator to get the voice signal. Demodulated signal is de-emphasized, filtered & amplified before applying it to loud speaker. Demodulated signal is also applied to DC amplifier. It produces DC voltage indicating the strength of received signal. This indicator is termed as RSSI (Received Signal Strength Indicator). RSSI signal is then sent back to cell site in order to help MTSO to monitor the received signal from the cell & decide about switching to another cell.(Hand Off) Demodulated signal is also applied to a band pass filter which selects out a band pass filter (BPF). BPF selects out the control audio tones & digital control data signal which are sent by cell site. These signals are applied to logic unit which produces the set & control signals for transmitter & receiver

Q.3 (ii) Give the classification of GSM logical channels and function of each channel [4](A) Classification-2M and functions-2M 1) GSM traffic channel (TCH) GSM TCH may be either full rate or half rate and may carry either digitized speech or user data.

(a) Full rate TCH: Full rate speech channel (TCH/FS): This channel carries user speech which is

digitized at a raw data rate if 13kbps. With GSM channel coding added to the digitized speech, this channel carries 22.8kbps.

Full rate data channel for 9600 bps(TCH/F9.6):This channel carries raw user data which is sent at 9600bps. With additional forward error correction coding applied by GSM standard the 9600bps data is sent at 22.8kbps.

Full rate data channel for 4800bps(TCH/F4.8): This channel carries raw user data which is sent at 4800bps. With additional forward error correction coding applied by GSM standard the 4800bps data is sent at 22.8kbps.

Full rate data channel for 2400bps (TCH/F2.4): This channel carries raw user data which is sent at 2400bps. With additional forward error correction coding applied by GSM standard the 2400bps data is sent at 22.8kbps.

(b) Half rate TCH: Half rate speech channel (TCH/HS): This channel has been designed to carry

digitized speech which is sampled at half rate of 6.5kbps with GSM channel coding added to the digitized speech the half rate speech channel will carry data at 11.4kbps.

Half rate data channel for 4800bps (TCH/H4.8): This channel arries raw user data which is sent at 4800bps. With additional forward error correction coding applied by GSM, this channel will carry data at 11.4kbps.

Half rate data channel for 2400bps (TCH/H2.4): This channel carries raw user data which is sent at 2400bps. With additional forward error correction coding applied by GSM, this channel will carry data at 11.4kbps.

2) GSM control channel (CCH): 1) Broadcast channel (BCH): i) Broadcast control channel (BCCH):The BCCH is a forward control channel that is

used to broadcast information such as cell and network identity, operating

Vidyala

nkar

Vidyalankar : T.Y. Diploma MC

10

characteristics of the cell (current control channel structure, channel availability and congestion).The BCCH also broadcast a list of channels that are currently in use within the cell.

ii) Frequency correction channel (FCCH): 1. The FCCH allows each subscriber unit to synchronize its internal frequency

standard (local oscillator) to the exact frequency of the base station. iv) Synchronization channel (SCH): SCH is used to identify the serving BS while

allowing each mobile to frame synchronizes with the BS. The frame number (FN) is sent with the base station identity code (BSIC) during the SCH burst.

v) Common control channel (CCCH): (a) Paging channel (PCH): The PCH provides paging signals from the BS to all

mobiles in the cell, and notifies a specific mobile of an incoming call which originates from PSTN. PCH may be used to provide cell broadcast ASCII text messages to all subscribers.

(b) Random Access Channel (RACH): The RACH is a reverse link channel used by a subscriber unit to acknowledge a page from the PCH and is also used by mobiles to originate a call.

(c) Access grant channel (AGCH): The AGCH is used by the BS to provide forward link communication to the mobile, and carries data which instructs the mobile to operate in a particular physical channel.

vi) Dedicated control channel (DCCH): (a) Stand-alone Dedicated control channel (SDCCH): The SDCCH carries

signaling data following the connection if the mobile with the BS, and just before TCH assignment issued by the BS. The SDCCH ensures that the mobile station and base station remain connected while the BS and MSC verifies subscriber unit.

(b) Slow Associated Control Channel (SACCH): On the forward link the SACCH is used to send slow but regularly changing control information to the mobile such a transmit power level instruction. On the reverse link the SACCH carries information about the received signal strength.

(c) Fast Associated Control Channel (FACCH): FACCH carries urgent messages and contains essentially the same type of information as SDCCH.

Q.3 (iii) Draw and explain microcell zone concept [4](A) [2 marks]

Vidyala

nkar

Prelim Question Paper Solution

11

[2 marks] The problem associated with sectoring technique is the increase in number of handoffs. This puts an additional load on the switching and control link elements of the mobile system. A solution to this problem is microcell concept. In this scheme, all the three or more zone sites represents 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. The antennas in zones are placed at the outer edges 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 hand-off. The base station will just switch the channel to the appropriate zone sit. 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 time and space by all the zones are also reused in the co- channels cells. The microcell concept is very useful along highways or in the busy urban areas.

Q.3 (iv) State any four specifications of UMTS [4](A) Any four specifications 1M EACH

1) Frequency spectrum:uplink 1920-1980 MHz Downlink 2110-2170 MHz 2) Channel Bandwidth:5 MHz 3) chip rate:3.84 Mcps 4) Duplexing Technique:FDD and TDD modes 5) Modulation scheme:Direct sequence CDMA with QPSK 6) Frame length:10 ms frame with 15 time slots 7) Coding technique:Orthogonal variable spreading factor(OVSF) 8) Service type:Multi-rate and multi-service

Q.3 (v) State the services of SS7 in detail [4](A) [Any four services 1mark each] SS7 SERVICES

a) Touchstar It is also known as CLASS. It is a group of switch Controlled Services that provides its users

with certain call management capabilities. It provides services such as call return, call forwarding, repeat dialing, call block, call tracing & caller ID.

b) 800 services It was introduced by bell System to provide toll-free access to the calling party to the

services & database which is offered by private parties. Cost associated with the processing of calls is paid by the service subscriber.800 Service is offered under two plans :

1) 800-NXX plan : The first 6 digits of an 800 call are used to select the interexchange carrier (IXC). 2) 800 database plan : The call is looked up in the database to determine the appropriate carrier & routing

information. 3) Alternate Billing Service & Line Information Database (ADB/LIDB) These services use the CCS network to enable the calling party to bill a call to a personal

number (third party number, calling card, or collect etc.) from any number 4) Performance of SS7

1) Performance of signaling network is studied by connection set-up time (response time) or the end-to-end Signaling information transfer time. The delays in the signaling point

Vidyala

nkar

Vidyalankar : T.Y. Diploma MC

12

(SP) and the STP depend on the specific hardware configuration & switching software implementation.

2) Congestion control in SS7 networks : With the increase in subscribers it is important to avoid congestion in the signaling

network under heavy traffic conditions.SS7 networking protocols provide several congestion control schemes, allowing traffic to avoid failed links & nodes.

Q.4 (a) Attempt any Three [12]Q.4 (a) (i) State specification of CDMA2000 [4](A) [Any four specifications 1mark each]

1) Frequency band:Any existing band 2) Minimum frequency bandrequired:1 X:2X1.25MHZ,3X:2X3.75MHZ 3) Chip rate:1x1.2288 mcps, 3x3.6864 mcps 4) Frame length:5ms,10ms,20ms 5) Power control rate:800 HZ 6) Spreading factor:4………..256 uplink b) Explain Radio aspects of GSM

Q.4 (a) (ii) Explain Redio aspect of GSM [4](A) [Any four radio aspects 1mark Each]

Sr Parameter Specification1 Reverse channel frequency 890-915MHZ 2 Forward channel frequency 935-960MHZ 3 ARFCN Number 0 to 124 and 975 to1023 4 Tx/Rx frequency spacing 45 MHZ 5 Tx/Rx Time slot spacing 3 Time slot 6 Modulation data rate 270.833333kbps 7 Frame period 4.615ms 8 User per frame 8 9 Time slot period 576.9microsecond 10 Bit period 3.692microsecond 11 Modulation 0.3GMSK 12 ARFCN channel spacing 200 kHZ 13 Interleaving 40ms 14 Voice coder bit rate 13.4kbps

Q.4 (a) (iii) State specification of GPRS [4](A) [Any four specification 1mark each] 1) Modulation:GMSK 2) Symbol rate:270 ksym/s 3) Modulation bit rate:270 kb/s 4) Radio data rate per time slot:22.8kb/s 5) User data rate per time slot:20kb/s 6) User data rate(8 time slot):160kb/s Q.4 (a) (iv) Define Hand off and list types of Handoff [4](A) When a mobile moves into a different cell while a conversation is in progress, the MSC

automatically transfers the call to a new channel belonging to the new base station. [2 mark] 1) Hard Handoff

2) Soft Handoff 3) Mobile assisted Handoff 4) Intersystem Handoff 5) Delayed Handoff 6) Queued Handoff

Vidyala

nkar

Prelim Question Paper Solution

13

Q.4 (b) Attempt any One [6]Q.4 (b) (i) Define Base station, mobile station, control channel, Roamer, Page, and MSC [6](A) [Each definition carries 1mark each] Base station: A fixed station in a mobile radio system used for radio communication with mobile stations.

Base stations are located at the center or on the edge of a coverage region and consists of radio channels and transmitter and receiver antennas mounted on a tower.

Mobile station: It is defined as a station in the cellular radio service which is used when in motion at an

unspecified location. Mobile stations may be held- held personal units (portables) or installed in vehicles (mobiles).

Control channel-Radio channels used for transmission of call setup, call request, call initiation and other beacon or control purposes.

Roaming: A MS which operates in a service area (market) other than that from which service

has been subscribed. Page: A Brief message which is broadcast over the entire service area,usually in a simulcast

fashion by many base stations at the same time. MSC: Switching center which coordinated the routing of calls in a large service area. In a

cellular radio system, the MSC connects the cellular base station and the mobiles to the PSTN. Q.4 (b)(ii) Draw and explain SS7 Protocol architecture [6](A) [4 mark]

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

Vidyala

nkar

Vidyalankar : T.Y. Diploma MC

14

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 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

Q.5 Attempt any four [16]Q.5 (i) Draw block diagram of logic unit and write the function of the each block [4](A) Diagram 2M and explanation 2 M The logic section used in the mobile phone handset contains the main control circuitry for the

mobile phone unit. It consist of following section

1. CPU 2. RAM 3. ROM 4. NAM(PROM) 5. INPUT INTERFACE CIRCUIT 6. CONTROL LOGIC

The entire mobile phone unit contains a PROM chip which is also known as NAM. The NAM holds the MIN (mobile identification number) which is the telephone number of mobile phone. The signals in the phone of serial data coming from the MTSO are applied to the control logic section. The bit rate of this signal is 10kbps. Also the signals from the transmitter section and receiver section of mobile phone unit are applied to the control logic section. The control signals from the control logic section keeps full control over the transmit & receiver frequencies & also the transmitted output power. The control signal also checks the received signal strength at the mobile phone unit by observing the RSSI signal & adjusts the transmitter power level.

Vidyala

nkar

Prelim Question Paper Solution

15

Q.5 (ii) Compare AMPS, IS95, GSM, NAMPS w.r.t frequency band and channel Bandwidth

[4]

(A) 2M for correct frequency band and 2M for correct channel Bandwidth Q.5 (iii) Draw and explain forward and reverse channel in IS95 [4](A) [2 mark]

[2 mark]

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) 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.

Parameter AMPS IS-95 GSM NAMPS Frequency band 824-894MHz 824-894 MHz

1.8-2.0 GHz 890-960 MHz 824-894 MHz

Frequency band 824-894MHz 824-894 MHz 1.8-2.0 GHz

890-960 MHz 824-894 MHz

Channel bandwidth 30 kHz 1.25 MHz 200 kHz 10 kHz

Vidyala

nkar

Vidyalankar : T.Y. Diploma MC

16

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.

Q.5 (iv) Draw and explain wireless Local Loop (WLL) [4](A) Operation [2 mark] Wireless Local Loop (WLL) is a new communications access method that uses radio waves for

transmission of information between customers and service provider sites, rather than traditional fixed methods such as copper or fiber optic.

The architecture consists of three major components: Wireless Access Network Unit (WANU) Wireless Access Subscriber Unit (WASU) Switching Function (SF)

Wireless Access Network Unit (WANU) It is an interface between underlying telephone network and wireless link that consists of Base

Station Transceivers (BTS) or Radio Ports (RP) , Radio Port Controller Unit (RPCU) or BSC Access Manager (AM), Home Location Register (HLR) RP is a base station of WLL system

RPCU - Radio Port Control Unit that connects a number of cell site based station transceivers and associated antennas. The RPCU provides the interface between the base stations and a telephone switch. It provides control and signaling functions for implementing the air interface to wireless handsets through the base stations Access Manager (AM)

The access manager/home location register (AM/HLR) handles authentication and privacy

Wireless Access Subscriber Unit (WASU) It is located at the subscriber. It translates wireless link into a traditional telephone connection. It provides an air interface toward the network and another interface to the subscriber. This interface includes protocol conversion and transcoding, authentication functions.

Switching Function It can be a digital switch. All the SF include ISDN algorithms. It is the transmission link

between WANU & SF can be microwave or cable.

[2 mark]

Vidyala

nkar

Prelim Question Paper Solution

17

Q.5 (v) Draw and operation LMDS with suitable Diagram [4](A) [2 marks] LMDS is one of the new proposed services and applications. It is in the early stages of

commercialization. In 1998, 1200MHz of the unused spectrum in the 27-31GHz band was auctioned by the US

government to support LMDS. Similar auctioned were held worldwide. Various spectrums were allotted for the LMDS. Most of these allocations share the frequencies with the teledesic band approved by the ITU for

broadband satellite systems. The teledesic band was originally established for the Motorola iridium system. LMDS is a fixed wireless system. The table given shows the total spectrum bandwidth of

various wireless systems in the US. It shows that the BW of 1300MHz has been allotted for LMDS.

The 1300MHz bandwidth of LMDS is sufficient to provide more than 200TV channels or 65000 full duplex voice channels.

The US LMDS band is 27.5 - 28.35 GHz, 29.1 – 29.25 GHz and 31.075 – 31.225 GHz. However LMDS has its own drawbacks. LMDS is a brand new, and an unproven system. The

equipment required for LMDS are millimeter wave equipment which are costly. The most important application of LMDS is the Local Exchange Carrier (LEC) network. It is

shown in the figure. In this network the LEC uses a very wide bandwidth ATM (asynchronous transfer mode) or

SONET (synchronous optical network) backbone switch. Such a switch can connect hundreds of megabits per second traffic to the internet, PSTN, or to

its own private network. The LMDS thus provides wireless broadband connectivity to the customers without using the cables.

Difficulties: The most important problem for LMDS of WLL is that of line of sight (LOS). If the antennas

can be seen, then only the transmission is successful. The other problem is that rain, snow and hail can create large changes in the channel gain

between the transmitter and receiver. [2 marks]

Q.5 (vi) Define cochannel interference, adjacent channel interference, system capacity

and MAHO Handoff [4]

(A) [2 mark each] Co-channel Interference

Frequency reuse - there are several cells that use the same set of frequencies co-channel cells co-channel interference

To reduce co-channel interference, co-channel cell must be separated by a minimum distance.

When the size of the cell is approximately the same co-channel interference is independent of the transmitted power co-channel interference is a function of R: Radius of the cell D: distance to the center of the nearest co-channel cell

Vidyala

nkar

Vidyalankar : T.Y. Diploma MC

18

Increasing the ratio Q=D/R, the interference is reduced. Q is called the co-channel reuse ratio A small value of Q provides large capacity A large value of Q improves the transmission quality - smaller level of co-channel

interference A tradeoff must be made between these two objectives Table : Co-channel Reuse Ratio for Some Values of N

System capacity: Consider a cellular system which has a total of S duplex channels. Each cell is allocated a group of k channels, k< s The S channels are divided among N cells. The total number of available radio channels S=KN The N cells which use the complete set of channels is called cluster. The cluster can be repeated M times within the system. The total number of channels, C, is

used as a measure of capacity C=MkN=MS The capacity is directly proportional to the number of replication M. The cluster size, N, is typically equal to 4, 7, or 12. Small N is desirable to maximize capacity. The frequency reuse factor is given by 1/N.

Q.6 Attempt any four [16]Q.6 (i) Draw block diagram of cellular Transmitter and write function of each block [4](A) [2 mark]

[2 marks]

It is a low power FM unit operating in the frequency range of 824 to 849 MHz. The Carrier is obtained from frequency synthesizer and is applied to phase Modulator along with the amplified voice signal.

Vidyala

nkar

Prelim Question Paper Solution

19

Modulator o/p converted using a mixer to final transmitter frequency. Mixer o/p is applied to Class C amplifier. The final amplifier stage is to designed to supply 3W to antenna. The automatic power control circuit controls the o/p power of the transmitter automatically, with the help of power o/p detector & DC amplifier. Transmitter o/p is fed to duplexer. Carrier i/p for the phase modulator & the local oscillator frequency signal for mixer are produced by frequency synthesizer. Transmitter o/p power is controlled by cell site & MTSO. Receiver picks up the special control signals & sends to APC that sets transmitter o/p power level.

Q.6 (ii) Compare WCDMA and GSM [4](A) 4 Marks for correct 4 four point of comparison

Parameter WCDMA GSM 1) Carrier spacing 5 MHZ 200 KHZ 2) Frequency reuse factor 1 1-18 3) Power control frequency 1.5 KHZ 2 HZ or lower 4) Quality control Radio resource

management algorithm

Network planning(frequency planning)

5) Frequency diversity

Multipath diversity with RAKE receiver

Frequenct hopping

6) Packet data Load –based packet scheduling

Time slot based scheduling with GPRS

7) DL transmit diversity

Supported for Improving downlink capacity

Not supported by standard but can be applied

Q.6 (iii) State two ways to improve frequency spectrum utilization [4](A) 1) Frequency Reuse 2) Call splitting

1) Frequency Reuse The figure alongside illustrates the concept of cellular frequency reuse. Here the Cells labelled with same letters use the same group of channels

Each cellular base station is allocated a group of radio channels to be used within a small geographic area called a cell. Base stations in adjacent cells are assigned channel groups which contain completely different channels than neighbouring cells. In the figure above A, B, C, D, E and F denote the channel groups of adjacent cells. The base station antennas are designed to achieve the desired coverage pattern (footprint) within the particular cell. By limiting the coverage area to within the boundaries of the cell, the same group of channels may be used in a different cells, provided they are sufficiently separated from one another. This is illustrated in the figure above. The minimum separation distance is governed by the tolerable co-channel interference.

Advantage of frequency reuse In the frequency reuse system, users in different cells may simultaneously use the same

frequency channel. Hence, it can drastically increase the spectrum efficiency.

2) Call splitting It is the process of splitting a congested cell into smaller cells each with its own base station and a

corresponding reduction in antenna height and transmitter power.

Vidyala

nkar

Vidyalankar : T.Y. Diploma MC

20

Q.6 (iv) Draw an explain block diagram of frequency synthesizer of mobile unit [4](A) [2 mark]

A frequency synthesizer is an electronic system for generating any of a range of frequencies from a single fixed time base or oscillator using two PLL. Frequency divider and VCO are the part of PLL. Frequency divider: Frequency dividers are used to generate a frequency that is a multiple of a reference frequency. These frequencies are then used for transmitters and receiver section VCO: A voltage-controlled oscillator or VCO is an oscillator whose oscillation frequency is controlled by a voltage input. The applied input voltage determines the instantaneous oscillation frequency. VCO‟s are used to vary the frequency of the carrier signal in accordance with the baseband signal amplitude variations. [2 marks]

Q.6 (v) Draw 4G wireless architecture and list it’s characteristics [4](A) 1) Faster and more reliable data rates than 100Mb/s [4 mark]

2) It has low cost in comparison to other generations (1G,2G,3G Networks) 3) It supports Bluetooth, wi-fi, wired and wireless Ad-hoc networking 4) It supports for multimedia services like teleconferencing and wireless internet 5) They have wide Bandwidth 6) 4G Networks are completely packet-switched networks 7) They have high internet speeds 8) Provide global mobility and service portability 9) The network security is tight

Q.6 (vi) Compare 3G and 4G w.r.t Mobile communication [4](A) [4 mark]

Requirement 3G 4G 1. Major Requirement

Driving Architecture Predominantly voice driven data was always add on.

Converged data and voice over IP

2. Network Architecture Wide area cell-based Hybrid-integration on wireless LAN (wi-fi, Bluetooth) and wide area.

3. Speeds 384 kbps to 2 Mbps 20 to 100 Mbps in mobile mode 4. Frequency band Dependent on country

(18002400MHZ) Higher frequency bands (2-8GHZ)

5. Bandwidth 5-20 MHZ 100MHZ(or more) 6. Switching Design

basis Circuit and packet All digital with packetized voice

7. Access Technologies W-CDMA, 1XRTT, EDGE OFDM and MC-CDMA 8. Forward error

correction Convolution rate 1/2, 1/3 Concatenated coding scheme

9. Component design Optimized Antenna, multiband adapters

Smart antennas, software multiband and wideband radio

10. IP IP 5.0 All IP (IP 6.0)

Vidyala

nkar