A

REPORT

ON

INDUSTRIAL TRAINING

(12th May 2010 – 18th June 2010)

AT

BHARTI HEXACOM LIMITED(AIRTEL),JAIPUR

Submitted for Partial Fulfillment Of

B.Tech Degree

IN

Electronics and Communication Engineering

Of

Rajasthan Technical University, Kota

Submitted by:Sumit Kumar Kaushik

B.Tech 7th Sem

GLOBAL INSTITUTE OF TECHNOLOGYITS-1, IT Park,Sitapura Jaipur-302022

Submitted to:Mr. Rishabh SharmaE.C.E Department

Table of Contents

ACKNOWLEDGEMENT..................................................................1

COMPANY PROFILE.......................................................................2

INTRODUCTION..............................................................................5

EVOLUTION OF GSM......................................................................8

DESCRIPTION.................................................................................10

CONCLUSION.................................................................................34

BIBLIOGRAPHY.............................................................................36

ANNEXURE………………………………………………………38

1

ACKNOWLEDGEMENT

I take this opportunity with much pleasure to express my sincere thanks and

gratitude to Mr.Vishal Tiwari (Manager, VAS), Airtel, Jaipur. It gives me

immense pleasure to extend my gratitude towards Mr. Keshav Sharma

(Quality Engineer), Airtel, Jaipur and the entire Network and Quality team of

AIRTEL, Jaipur for providing their cooperation, constructive criticism,

valuable guidance and constant encouragement.

In addition, I wish to thank Airtel, Jaipur office to provide me the opportunity

to acquire the experience of knowing the corporate world and also providing

the required facilities, well working systems, besides complete collection of all

latest technology software’s.

I am especially grateful to the professors and lecturers of our institute ‘Global

Institute of Technology’, who has been training us, since the first day, with the

knowledge and support in the most lucid manner.

It was really a good experience working in a professionally managed firm and

learning from such good and knowledgeable people. I hope it will really help

me in future.

(Sumit Kumar Kaushik)

2

COMPANY PROFILE

Bharti Airtel Limited formerly known as Bharti Tele-Ventures LTD (BTVL) is

an Indian company offering telecommunication services in around 19

countries. It is the largest cellular service provider in India, with more than 137

million subscriptions as of June 2010. Bharti Airtel is the world's third largest,

single-country mobile operator and fifth largest telecom operator in the world

in terms of subscriber base. It also offers fixed line services and broadband

services. It offers its telecom services under the Airtel brand and is headed

by Mr. Sunil Bharti Mittal, who is the Chairman & Managing Director of the

Company. The company also provides land-line telephone services, under the

trade name ‘Touchtel’ and broadband Internet access (DSL) in over 96 cities in

India.

3

Bharti Airtel is known for being the first mobile phone company in the world

to outsource everything except marketing and sales and finance. Its network

(base stations, microwave links, etc.) is maintained by Ericsson and Nokia

Siemens Network, business support by IBM and transmission towers by

another company. Ericsson agreed for the first time, to be paid by the minute

for installation and maintenance of their equipment rather than being paid up

front. This enables the company to provide pan-India phone call rates of

less than Rs. 1/minute. During the last financial year (2009-10), Bharti has

roped in a strategic partner Alcatel-Lucent to manage the network

infrastructure for the Telemedia Business.

The tabulated summary of various partnering companies is as under:

Network

Equipment

Mobile Services Nokia Siemens, Ericsson, Huawei

Telemedia & Long

Distance Services

Nokia Siemens, Juniper, Cisco,

Alcatel Lucent, ECI, Tellabs

Information Technology IBM

Call Centre Operations

IBM Daksh, Hinduja TMT,

Teleperformance,

Mphasis, First source & Aegis

The company is structured into four strategic business units:

4

Mobile,

Telemedia,

Enterprise, and

Digital TV

The mobile business offers services in 18 countries across the Indian

Subcontinent and Africa. The Telemedia business provides broadband, IPTV

and telephone services in 89 Indian cities. The Digital TV business provides

Direct-to-Home TV services across India. The Enterprise business provides

end-to-end telecom solutions to corporate customers and national and

international long distance services to telcos. In June 2010, Bharti Airtel as

part of its global expansion strategy acquired Zain Telcom of Kuwait. Bharti

Airtel through the Zain deal has its business space in 15 African countries. On

August 11, 2010, Bharti Airtel announced that it would acquire 100% stake

in Telecom Seychelles taking its global presence to 19 countries.

Globally, Bharti Airtel is the 3rd largest in-country mobile operator by

subscriber base, behind China Mobile and China Unicom.

Fig. 1.1 Coverage map of Bharti Airtel across 19 countries

INTRODUCTION

5

.

GSM stands for ‘Global Services for Mobile communication' and is an open,

digital cellular technology used for transmitting mobile voice and data

services. GSM supports voice calls and data transfer speeds of up to 9.6 kbit/s,

together with the transmission of SMS (Short Message Service).

This technology is globally accepted and most popular among all countries. It

is started in Europe to integrate all countries with wireless communication.

Earlier each country in Europe has its own standard for wireless

communication ,so due to this a person cannot use the same mobile in two

different country and cannot even communicate with the same mobile in

different countries, so due to this fragmentation problem occurred. So to

overcome this problem European Union (EU) came with GSM technology that

is accepted by whole continent and standardized by ITU-T. It is a 2 G

technology and world’s first cellular technology and it is most popular 2G

technology. Today GSM operator has largest customer base. In India total

cellular operator have more than 550 million customers and GSM has more

than 400 million customer bases alone. It is a second generation cellular

standard developed to cater voice services and data delivery using digital

modulation.

Objectives of GSM

6

To eliminate the fragmentation problem in European Union.

To allow interaction with ISDN and PSTN.

The Goals of GSM

Improved spectrum efficiency

International roaming

Low-cost mobile sets and base stations

High-quality speech

Compatibility with ISDN and other telephone

Company services.

Support for new services

Specifications and Characteristics for GSM:

Frequency band – the frequency range specified for GSM is 1,850 to

1,990 MHz (mobile station to base station).

Duplex distance – the duplex distance is 80 MHz. Duplex distance is the

distance between the uplink and downlink frequencies. A channel has

two frequencies, 80 MHz apart.

Channel separation – the separation between adjacent carrier

frequencies. In GSM, this is 200 kHz.

7

Modulation – Modulation is the process of sending a signal by changing

the characteristics of a carrier frequency. This is done in GSM via

Gaussian minimum shift keying (GMSK).

Transmission rate – GSM is a digital system with an over-the-air bit rate

of 270 kbps.

Access method – GSM utilizes the time division multiple access

(TDMA) concept. TDMA is a technique in which several different calls

may share the same carrier. Each call is assigned a particular time slot.

Speech coder – GSM uses linear predictive coding (LPC). The purpose

of LPC is to reduce the bit rate. The LPC provides parameters for a filter

that mimics the vocal tract.

8

EVOLUTION OF GSM

In 1982, the European Conference of Postal and Telecommunications

administrations (CEPT) created the Group Special Mobile (GSM) to develop a

standard for a mobile telephone system that could be used across Europe. In

1987, a memorandum of understanding was signed by 13 countries to develop

a common cellular telephone system across Europe. Finally the system created

by SINTEF led by Torleiv Maseng was selected.

In 1989, GSM responsibility was transferred to the European

Telecommunications Standards Institute (ETSI) and phase I of the GSM

specifications were published in 1990. The first GSM network was launched in

1991 by Radio linja in Finland with joint technical infrastructure maintenance

from Ericsson. By the end of 1993, over a million subscribers were using GSM

phone networks being operated by 70 carriers across 48 countries.

GSM around the world

9

GSM statistics in India

10

DESCRIPTION

The basic architecture of the GSM is described in the figure below:

The abbreviations used in the figure above are described herein under:

HLR- Home Location Register:                  

                

HLR is database, which holds very important information of subscribers. It is

mostly known for storing and managing information of subscribers. It contains

subscriber service profile, status of activities, information about locations and

permanent data of all sorts. When new connections are purchased, these

subscribers are registered in HLR of mobile phone companies.

11

MS-Mobile station:

It consists of mobile equipment and SIM. At the time of manufacturing, an

international mobile equipment number (IMEI) is programmed in ME.A SIM

is required to activate the GSM services. A international mobile subscriber

identification (IMEI) number is programmed along with security parameter

and algorithm. The called number is not linked to ME but to SIM.A SIM has

following data stored in it. MSISDN (mobile subscriber isdn) IMSI

(international mobile subscriber identity) - 15 digit number. TMSI (temporary

mobile subscriber identity) – 4 octets, allocated by VLR, continuously

changed.IMEI (international mobile equipment identity) unique, permanently

assigned to MS.

12

AUC- Authentication Center:

AUC is small unit which handles the security end of the system. Its major task

is to authenticate and encrypt those parameters which verify user’s

identification and hence enables the confidentiality of each call made by

subscriber. Authentication center – AUC makes sure mobile operators are safe

from different frauds most likely to happen when hackers are looking for even

smallest loop wholes in systems.

MSC- Mobile Services Switching Center:

MSC is also important part of SS, it handles technical end of telephony. It is

build to perform switching functionality of the entire system. It’s most

important task is to control the calls to and from other telephones, which

means it controls calls from same networks and calls from other networks. Toll

ticketing, common channel signaling, network interfacing etc are other tasks

which MSC is responsible for.

.

13

VLR- Visitor Location Register:

VLR performs very dynamic tasks; it is database which stores temporary data

regarding subscribers which is needed by Mobile Services Switching Center-

MSC VLR is directly connected to MSC, when subscribe moves to different

MSC location, Visitor location register – VLR integrates to MSC of current

location and requests the data about subscriber or Mobile station (MS) from

the Home Location Register –HLR. When subscriber makes a call the Visitor

location register-VLR will have required information for making call already

and it will not required to connect to Home Register Location - HRL again.

BSS-The Base Station System:

The base station system have very important role in mobile communication.

BSS are basically outdoor units which consist of iron rods and are usually of

high length. BSS are responsible for connecting subscribers (MS) to mobile

networks. All the communication is made in Radio transmission. The Base

station System is further divided in two systems. These two systems, they are

BSC, and BTS.

14

BTS – The Base Transceiver Station:

Subscriber, MS (Mobile Station) or mobile phone connects to mobile network

through BTS; it handles communication using radio transmission with mobile

station. As name suggests, Base transceiver Station is the radio equipment

which receive and transmit voice data at the same time. BSC control group of

BTSs.

BASE TRANSIEVER STATION (BTS)

15

BSC – The Base Station Controller:

The Base Station normally controls many cells; it registers subscribers,

responsible for MS handovers etc. It creates physical link between subscriber

(MS) and BTS, then manage and controls functions of it. It performs the

function of high quality switch by handover over the MS to next BSC when

MS goes out of the current range of BTS, it helps in connecting to next in

range BTS to keep the connection alive within the network. It also performs

functions like cell configuration data, control radio frequency in BTS.

16

SIM-Subscriber Identity Module:

One of the key features of GSM is the Subscriber Identity Module, commonly

known as a SIM card. The SIM is a detachable smart card containing the user's

subscription information and phone book. This allows the user to retain his or

her information after switching handsets. Alternatively, the user can also

change operators while retaining the handset simply by changing the SIM.

OSS -The Operation and Support System:

OMC- Operations and maintenance center is designed to connect to equipment

of MSC- Mobile Switching Center and BSC-Base Station Controller. The

implementation of OMC is called OSS-The Operations and Support

System.OSS helps in mobile networks to monitor and control the complex

systems. The basic reason for developing operation and support system is to

provide customers a cost effective support and solutions. It helps in managing,

centralizing, local and regional operational activities required for GMS

networks.

17

Authentication & Encryption:

Authentication: - Whenever a MS requests access to a network, the network

must authenticate the MS. Authentication verifies the identity and validity of

the SIM card to the network and ensures that the subscriber is authorized

access to the network.

Encryption:- In GSM, encryption refers to the process of creating

authentication and ciphering crypto variables using a special key and an

encryption algorithm.

Ciphering:- Ciphering refers to the process of changing plaintext data into

encrypted data using a special key and a special encryption algorithm.

Transmissions between the MS and the BTS on the Um link, are enciphered.

Ki:- The Ki is the individual subscriber authentication key. It is a 128-bit

number that is paired with an IMSI when the SIM card is created. The Ki is

only stored on the SIM card and at the Authentication Center (AuC). The Ki

should never be transmitted across the network on any link.

RAND:- The RAND is a random 128-bit number that is generated by the Auc

when the network requests to authenticate a subscriber. The RAND is used to

generate the Signed Response (SRES) and Kc crypto variables.

Signed Response:- The SRES is a 32-bit crypto variable used in the

authentication process. The MS is challenged by being given the RAND by the

network; the SRES is the expected correct response. The SRES is never passed

on the Um (Air) interface. It is kept at the MSC/VLR, which performs the

authentication check.

18

A3 Algorithm:- The A3 algorithm computes a 32-bit Signed Response

(SRES). The Ki and RAND are inputted into the A3 algorithm and the result is

the 32-bit SRES. The A3 algorithm resides on the SIM card and at the AuC.

A8 Algorithm:- The A8 algorithm computes a 64-bit ciphering key (Kc). The

Ki and the RAND are inputted into the A8 algorithm and the result is the 64-

bit Kc. The A8 algorithm resides on the ISM card and at the AuC.

Kc:- The Kc is the 64-bit ciphering key that is used in the A5 encryption

algorithm to encipher and decipher the data that is being transmitted on the

Um interface.

A5:- The A5 encryption algorithm is used to encipher and decipher the data

that is being transmitted on the Um interface. The Kc and the plaintext data are

inputted into the A5 algorithm and the output is enciphered data. The A5

algorithm is a function of the Mobile Equipment (ME) and not a function of

the SIM card. The BTS also makes use of the A5 algorithm.

There are three versions of the A5 algorithm:

 A5/1:- The current standard for U.S. and European networks. A5/1 is a stream

cipher.

 A5/2:- The deliberately weakened version of A5/1 that is intended for export

to non-western countries. A5/2 is a stream cipher.

 A5/3:- A newly developed algorithm not yet in full use. A5/3 is a block

cipher.

Triplets: - The RAND, SRES, and Kc together are known as the Triplets. The

AuC will send these three crypto variables to the requesting MSC/VLR so it

can authenticate and encipher.

19

GSM Control Channels:

1. The Broadcast Channel [BCH].

2. The Common Control Channel [CCCH]

3. The Dedicated Control Channel [DCCH]

1. The Broadcast Channel [BCH]:

It operates on the forward link of specific ARFCN within each cell, and transmits data only in the first time slot (TS0) of certain GSM frames.

It serves as a TDMA bacon channel for any nearby mobile to identify & lock on to.

It provides synchronization for all mobiles within the cell.

It is occasionally monitored by mobiles in neighboring cell so that received power MAHO decisions may be made by out of cell users.

The BCH is defined by three separate channels.

a. Broadcast Control Channel [BCCH].

b. Frequency Correction Channel [FCCH].

c. Synchronization Channel [SCH].

a) Broadcast Control Channel [BCCH]

It is a forward control channel that is used to broadcast following information.

Cell & Network Identity.

Operating characteristics of cell such as current control channel structure, channel availability and congestion.

List of channels that are currently in use within the cell.

20

Information about BCCH is carried for the neighboring cells.

b) Frequency Correction Channel [FCCH]

It is a special data burst which occupies TS0 for the very first GSM frame & is repeated every 10 frames within a control channel multi frame.

It allows each subscriber unit to synchronize its internal frequency to the exact frequency of the BTS.

c) Synchronization Channel [SCH]:

It is broadcast in TS0 of the frame immediately following the FCCH frame.

It is also repeated every 10 frames within the control channel multi frame.

It is used to identify serving the BTS that is it is GSM BTS (Mobile transmits BSIC (Base Station Identity Code); BSIC can only be decoded by GSM BTS.

It allows mobile to frame synchronize with BTS.

2. Common Control Channel [CCCH]

On the Broadcast channel ARFCN, these channels occupy TS 0 of every GSM frame that is not otherwise used by the BCH.

The CCCH consists of three different channels,

o Paging Channel [PCH]

o Random Access Channel [RACH]

o Access Grant Channel [AGCH]

a. Paging Channel [PCH]:

21

It is used to broadcast the following information.

Paging Signals from the BTS to all mobiles in the cell, & notify a specific mobile of an incoming call which originates from PSTN.

The IMSI of the target subscribers, along with a request for acknowledgement from the mobile unit on the RACH.

b. Random Access Channel [RACH]:

It is used for,

To acknowledge a Page from the PCH.

To originate call.

All mobiles must access or respond to PCH alert within TS 0 of a GSM frame.

c. Access Grant Channel [AGCH]:

It is used for:

To respond RACH sent by a mobile in the previous CCCH frame.

To carry data this instructs the mobile to operate in a particular physical channel with a particular dedicated control channel.

3. Dedicated Control Channels [DCCH]:

These channels are bi directional & have the same format & function on both forward & reverse link.

They may exist in any time slot & on any ARFCN except TS 0.

a) Stand Alone Dedicated Control Channel [SDCCH].

b) Slow Associated Control Channel [SACCH].

22

c) Fast Associated Control Channel [FACCH].

a) Stand Alone Dedicated Control Channel [SDCCH]:

It is used to send authentication and alert messages as the mobile synchronizes itself with the frame structure and waits for TCH.

It is used for location updating.

b) Slow associated Control Channel [SACCH]:

It is always associated with a TCH or a SDCCH & maps onto the same physical channel.

On the forward link it is used to send changing control information to the mobile, such as transmit power level instructions.

The reverse SACCH carries information about the received signal strengths, quality of TCH & BCH measurement results from neighboring cells.

c) Fast Associated Control Channel [FACCH]:

It is assigned whenever a SDCCH has not been dedicated for a particular user and there is a urgent message to be conveyed.

It is assigned only to a traffic channel & relies on frame stealing to gain access to the traffic channel.

Value added services

Call waiting:

23

With Call Waiting on a Hutch phone, you can receive and hold an incoming

call when you are already talking to another person. When this service is

activated, the network notifies you of a new incoming call while you have a

call in progress, which means that if another person tries calling you midway

through a conversation, he/she will hear a message informing him/her that

your line is busy, while you will hear beeps at intervals.

Call Divert:

In case you are busy in a meeting, or if your cell phone is switched off, you

can forward incoming calls to a landline or another mobile phone - where

someone can receive messages on your behalf. You can also forward an

incoming call while speaking to someone.

Voice response services:

By using these services one can access information, download ringtones and

logos, and more. For this one has to just dial and speak on a no. for the desired

service. With Hutch World, one can enjoy a host of GPRS-based services

exclusively on Hutch GPRS phone. From astrology to photo messaging,

gaming, chat, news and even internet access.

Mail:

One can now send an SMS - without even using a mobile phone, from

wherever they are. All they need to do is type in their message and send it as e-

mail.

Roaming:

Roaming is defined as the ability for a cellular customer to automatically make

& receive voice calls, send & receive data, or access other services when

24

traveling outside the geographical coverage area of the home network, by

means of using a visited network.

If the visited network is in the same country as the home network, this is

known as National Roaming. If the visited network is outside the home

country, this is known as International Roaming (the term Global Roaming has

also been used).

If the visited network operates on a different technical standard than the home

network, this is known as Inter-standard roaming.

GSM Roaming, which involves roaming between GSM networks, offers the

convenience of a single number, a single bill and a single phone with

worldwide access to over 205 countries. The convenience of GSM Roaming

has been a key driver behind the global success of the GSM Platform.

Mobile subscriber identities in GSM

International Mobile Subscriber Identity (IMSI):

An IMSI is assigned to each authorized GSM user. It consists of a mobile

country code (MCC), mobile network code (MNC) (to identify the PLMN),

and a PLMN unique mobile subscriber identification number (MSIN). The

IMSI is the only absolute identity that a subscriber has within the GSM

system. The IMSI consists of the MCC followed by the MNC and MSIN and

shall not exceed 15 digits.

Temporary Mobile Subscriber Identity (TMSI)

A TMSI is a MSC-VLR specific alias that is designed to maintain user

confidentiality. It is assigned only after successful subscriber authentication.

25

The correlation of a TMSI to an IMSI only occurs during a mobile subscriber’s

initial transaction with an MSC (for example, location updating). Under certain

condition (such as traffic system disruption and malfunctioning of the system),

the MSC can direct individual TMSIs to provide the MSC with their IMSI.

Mobile Station ISDN Number:

The MS international number must be dialed after the international prefix in

order to obtain a mobile subscriber in another country. The MSISDN numbers

is composed of the country code (CC) followed by the National Destination

Code (NDC), Subscriber Number (SN), which shall not exceed 15 digits. Here

too the first two digits of the SN identify the HLR where the mobile subscriber

is administrated.

The Mobile Station Roaming Number (MSRN):

The MSRN is allocated on temporary basis when the MS roams into another

numbering area. The MSRN number is used by the HLR for rerouting calls to

the MS. It is assigned upon demand by the HLR on a per-call basis. The

MSRN for PSTN/ISDN routing shall have the same structure as international

ISDN numbers in the area in which the MSRN is allocated. The HLR knows in

what MSC/VLR service area the subscriber is located. At the reception of the

MSRN, HLR sends it to the GMSC, which can now route the call to the

MSC/VLR exchange where the called subscriber is currently registered.

International Mobile Equipment Identity:

26

The IMEI is the unique identity of the equipment used by a subscriber by each

PLMN and is used to determine authorized (white), unauthorized (black), and

malfunctioning (gray) GSM hardware. In conjunction with the IMSI, it is used

to ensure that only authorized users are granted access to the system.

Subscriber Authentication Key (Ki):

It is used to authenticate the SIM card.

Pin Unblocking Key (PUK)

In case of PIN, the PUK is needed for unlocking the SIM again. PUK is

numeric only, with eight digits. If a correct PUK is entered, an indication is

given to the user. After 10 consecutive incorrect entries the SIM is blocked.

Either the IMSI or the MSISDN Number may access the subscriber data. Some

of the parameters like IAI will be continuously updated to reflect the current

location of the subscriber. The SIM is capable of storing additional

information such as accumulated call charges. This information will be

accessible to the customer via handset key entry.

Personal Identity Number (PIN)

It is used to unlock the MS. If one enters the wrong PIN three times it will lock

the SIM. The SIM can be protected by use of PIN password.

27

GSM Frequency Bands

There are a total of fourteen different recognized GSM

frequency bands. These are defined in 3GPP TS 45.005.

28

Band Uplink

(MHz)

Downlink

(MHz) Comments

380 380.2 - 389.8 390.2 - 399.8  

410 410.2 - 419.8 420.2 - 429.8  

450 450.4 - 457.6 460.4 - 467.6  

480 478.8 - 486.0 488.8 - 496.0  

710 698.0 - 716.0 728.0 - 746.0  

750 747.0 - 762.0 777.0 - 792.0  

810 806.0 - 821.0 851.0 - 866.0  

850 824.0 - 849.0 869.0 - 894.0  

900 890.0 - 915.0 935.0 - 960.0

P- GSM , i.e. Primary

or standard GSM

allocation

900 880.0 - 915.0 925.0 - 960.0

E- GSM , i.e.

Extended GSM

allocation

900 876.0 - 915 921.0 - 960.0 R- GSM , i.e. Railway

GSM allocation

900 870.4 - 876.0 915.4 - 921.0 T- GSM

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Band Uplink

(MHz)

Downlink

(MHz) Comments

1800 1710.0 -

1785.0

1805.0 -

1880.0

1900 1850.0 -

1910.0

1930.0 -

1990.0

 

There are three different frequency bands on which mobile phones are usually

operates and these are Dual Band, Tri-Band and Quad Band.

Dual Band : Dual frequency band operates on 900MHz and 1800 MHz,

that means mobile phone that supports dual band can be operated

anywhere in the world where 900 MHz and 1800 MHz frequencies are

used. Dual Band GSM networks usually found in all continents Europe,

Asia, Africa, Australia and South America.

Tri-Band: three frequencies are supported in Tri Band, these

frequencies are 900 MHz, 1800MHz and 1900 MHz Tri band is also

30

supported all around the world these days.

Quad-Band: Quad Band supports four frequencies which are 850 MHz,

900 MHz, 1800 MHz , 1900 MHz Quad band also enables GSM phones

to road almost anywhere in the world. All countries support GSM

networks hence make communication possible.

Handover:

Handover, or handoff as it is called in North America, is the switching of an

ongoing call to a different channel or cell.  There are four different types of

handover in the GSM system, which involve transferring a call between

Channels (time slots) in the same cell,

Cells (Base Transceiver Stations) under the control of the same Base

Station Controller (BSC),

Cells under the control of different BSCs, but belonging to the same

Mobile services Switching Center (MSC), and

Cells under the control of different MSCs.

The first two types of handover, called internal handovers, involve only one

Base Station Controller (BSC).  To save signaling bandwidth, they are

managed by the BSC without involving the Mobile service Switching Center

(MSC), except to notify it at the completion of the handover.  The last two

types of handover, called external handovers, are handled by the MSCs

involved.  Note that call control, such as provision of supplementary services

and requests for further handoffs, is handled by the original MSC.

Handovers can be initiated by either the mobile or the MSC (as a means of

traffic load balancing).  During its idle time slots, the mobile scans the

31

Broadcast Control Channel of up to 16 neighboring cells, and forms a list of

the six best candidates for possible handover, based on the received signal

strength.  This information is passed to the BSC and MSC, and is used by the

handover algorithm.

The algorithm for when a handover decision should be taken is not specified in

the GSM recommendations.  There are two basic algorithms used, both closely

tied in with power control. This is because the BSC usually does not know

whether the poor signal quality is due to multipath fading or to the mobile

having moved to another cell.  This is especially true in small urban cells.

The 'minimum acceptable performance' algorithm [Bal91] gives precedence to

power control over handover, so that when the signal degrades beyond a

certain point, the power level of the mobile is increased.  If further power

increases do not improve the signal, then a handover is considered.  This is the

simpler and more common method, but it creates 'smeared' cell boundaries

when a mobile transmitting at peak power goes some distance beyond its

original cell boundaries into another cell.

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Key Features

SIM (Subscriber Identity Module)

It is a memory device which is used to store the information of user such as

user privacy number, 4 digit PIN number, subscriber identification number and

user information. Called number is not associated with mobile station but to

SIM.

Increased Capacity

It provides better channel capacity than analog system. It provides 25KHZ per

user, that means eight conversation per 200KHZ channel pair(a channel pair

consists of a forward channel and a reverse channel). Channel coding and

modulation provided to enhance the channel capacity and from this 12 DB is

achieved as a channel to interference ratio(C/I ration), as compare to 18db of

analog system.

Frequency Hopping

It is a feature of GSM system in which frequency in a single channel

continuously hops and resultant provides a better coverage to a specific area.

Mobile Assisted Handover (MAHO)

GSM uses Mobile assisted handover technique. The mobile itself carries out

the signal strength and quality measurement of its server and signal strength

measurement of its neighbors. This data is passed on the Network which then

uses sophisticated algorithms to determine the need of handover.

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Discontinuous Transmission

In this GSM has a advantage of preventing system from interference and noise

by offsetting the silent time between the conversation and by blocking the

undesired signals.

Support of Short Service Message (SMS)

GSM has a advantage of short service messages assisted by paging channel of

system.

Frequency Reuse

GSM has a advantage of frequency reuse pattern from which same frequency

can be used in different cells. Normally 124 carriers are provided by the GSM

system and if we multiply it with the 7 time slots used for traffic than we get

868 numbers of calls can be made and that is very less in number. so to

overcome this problem same RF carrier is used for several conversation in

different cells and for this there is regular pattern is defined. The pattern to be

used depends on the traffic requirement and spectrum availability. Some

typical patter are 4/12 , 7/21 etc.

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Future Opportunities for GSM:

2nd Generation

GSM -9.6 Kbps (data rate)

2.5 Generation ( Future of GSM)

HSCSD (High Speed ckt Switched data)

Data rate : 76.8 Kbps (9.6 x 8 kbps)

GPRS (General Packet Radio service)

Data rate: 14.4 - 115.2 Kbps

EDGE (Enhanced data rate for GSM Evolution)

Data rate: 547.2 Kbps (max)

3 Generation

WCDMA(Wide band CDMA)

Data rate : 0.348 – 2.0 Mbps

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CONCLUSION

During the period of Evolution of mobile communication technologies various

systems were introduced and deployed to achieve standardization in mobile

industry, but all the efforts were failed. Multiple issues were sustained like

incompatibility of systems, development of digital radio frequency. That is,

when GSM (Global System for Mobile Communication) Technology was

introduced and problems like standardization, incompatibility etc were

overcame. TDMA solution was chosen in 1987, it is narrowband system and

TDMA standards for Time Division Multiple access.

In 1991 in Finland. GSM based mobile phones are operated on TDMA

Systems, in TDMA single radio frequency is offered to users with any

interference. After all these years, GSM is now the largest mobile

communication technology worldwide, all manufacturers of Mobile phones

develop their products based on GSM, and all mobile companies provide their

subscribers GSM networks.

GSM technology facilitates with high speed integrated data, voice data, fax,

mail, voice mail and mostly used SMS feature. GSM also make sure that all

the communication made between networks are secured and protected from

intruders and frauds.

.SM actually brought the concept of being Mobile way beyond the limits. It

enabled us to communicate across the continents.

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GSM supports multiple frequency levels like 900 MHz, 1800 MHz, 1900 MHz

1900MHz frequency is used in North America where as 1800MHz is used in

other parts of the world. Different frequency bands are used by different

mobile phone operators.

Moreover, there are over 700 GSM networks available in the world operating

in their respective countries and providing international roaming services

courtesy GSM technology. There are over 2 billion GSM subscribers in the

world. Countries which are using GSM networks on larger scales are Russia,

china Pakistan, United States, India.

Giver the above facts and very good voice quality, support useful services and

standards, delivered by GSM, it is expected that GSM shall remain the

prominent technology for offering the mobile telephony.

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BIBLIOGRAPHY

1. www.gsmworld.com 2. www.gsacom.com 3. www. whytelecom.com4. www . wikipedia . com 5. www.google.com 6. www.ask.com7. www.search.com

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Annexure

GSM: Global System for Mobile Communication

CEPT: Conference of European Posts and Telecommunications

ISDN: Integrated Services Digital Network

SIM: Subscriber Identity Module

VAS: Value Aided Services

BSS: The Base Station Subsystem

NSS: The Network and Switching Subsystem

OSS: The Operation and Support Subsystem

FDMA: Frequency Division Multiple Access

TDMA: Time Division Multiple Access

HLR: Home Location Register

MS: Mobile station

VLR: Visitor Location Register

AUC: Authentication Center

MSC: Mobile Services Switching Center

BTS : The Base Transceiver Station

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