Training Report On Gsm 445t2c

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 to: Mr. Rishabh Sharma E.C.E Department

Submitted by: Sumit Kumar Kaushik B.Tech 7th Sem

GLOBAL INSTITUTE OF TECHNOLOGY ITS-1, IT Park,Sitapura Jaipur-302022

Table of Contents ACKNOWLEDGEMENT..................................................................1 COMPANY PROFILE.......................................................................2 INTRODUCTION..............................................................................5 EVOLUTION OF GSM......................................................................8 DESCRIPTION.................................................................................10 CONCLUSION.................................................................................34 BIBLIOGRAPHY.............................................................................36 ANNEXURE………………………………………………………38

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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 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)

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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 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.

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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 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: Mobile Services

Nokia Siemens, Ericsson, Huawei

Telemedia & Long

Nokia Siemens, Juniper, Cisco,

Distance Services

Alcatel Lucent, ECI, Tellabs

Network Equipment

Information Technology

IBM IBM Daksh, Hinduja TMT,

Call Centre Operations

Teleperformance, Mphasis, First source & Aegis

The company is structured into four strategic business units:

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• 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

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INTRODUCTION

.

GSM stands for ‘Global Services for Mobile communication' and is an open, digital cellular technology used for transmitting mobile voice and data services. GSM s 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.

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Objectives of GSM • 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. • 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. 8

• 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.

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EVOLUTION OF GSM In 1982, the European Conference of Postal and Telecommunications istrations (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 t 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

10

GSM statistics in India

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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 :

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 ed in HLR of mobile phone companies.

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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.

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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 ’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.

.

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VLR- Visitor Location : VLR performs very dynamic tasks; it is database which stores temporary data regarding subscribers which is needed by Mobile Services Switching CenC VLR is directly connected to MSC, when subscribe moves to different MSC location, Visitor location – VLR integrates to MSC of current location and requests the data about subscriber or Mobile station (MS) from the Home Location –HLR. When subscriber makes a call the Visitor location -VLR will have required information for making call already and it will not required to connect to Home 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.

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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)

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BSC – The Base Station Controller: The Base Station normally controls many cells; it s 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.

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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 's subscription information and phone book. This allows the to retain his or her information after switching handsets. Alternatively, the can also change operators while retaining the handset simply by changing the SIM.

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OSS -The Operation and 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 System.OSS helps in mobile networks to monitor and control the complex systems. The basic reason for developing operation and system is to provide customers a cost effective and solutions. It helps in managing, centralizing, local and regional operational activities required for GMS networks.

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.

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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 ed on the Um (Air) interface. It is kept at the MSC/VLR, which performs the authentication check. 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 64bit Kc. The A8 algorithm resides on the ISM card and at the AuC.

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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.

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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 s. • 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.

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• 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. • 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. •

2.

It allows mobile to frame synchronize with BTS.

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] 23

o Access Grant Channel [AGCH]

a. Paging Channel [PCH]: 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]:

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• 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].

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 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. 25

Value added services Call waiting: 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, 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 email. 26

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 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 . 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. 27

Temporary Mobile Subscriber Identity (TMSI) A TMSI is a MSC-VLR specific alias that is designed to maintain confidentiality. It is assigned only after successful subscriber authentication. 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 istrated. 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 ed.

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International Mobile Equipment Identity: 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 s 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 . 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 .

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GSM Frequency Bands

There are a total of fourteen different recognized GSM frequency bands. These are defined in 3GPP TS 45.005.

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Band

Uplink (MHz)

Downlink

Comments

(MHz)

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 P-GSM, i.e. Primary

900

890.0 - 915.0 935.0 - 960.0

or standard GSM allocation E-GSM, i.e.

900

880.0 - 915.0 925.0 - 960.0

Extended GSM allocation

900

876.0 - 915

900

870.4 - 876.0 915.4 - 921.0 T-GSM

1800

1710.0 1785.0

921.0 - 960.0

R-GSM, i.e. Railway

1805.0 1880.0

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GSM allocation

Band

1900

Uplink (MHz)

1850.0 1910.0

Downlink

Comments

(MHz)

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 s 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 ed in Tri Band, these frequencies are 900 MHz, 1800MHz and 1900 MHz Tri band is also ed all around the world these days. Quad-Band: Quad Band s 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 GSM networks hence make communication possible. 32

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 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 ed to the BSC and MSC, and is used by the handover algorithm. 33

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 such as privacy number, 4 digit PIN number, subscriber identification number and 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 , 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 ed 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. 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 s 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 s 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, 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.com

4. www.wikipedia.com 5. www.google.com 6.

www.ask.com

7.

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 Subsystem FDMA: Frequency Division Multiple Access TDMA: Time Division Multiple Access HLR: Home Location MS: Mobile station VLR: Visitor Location AUC: Authentication Center MSC: Mobile Services Switching Center

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BTS : The Base Transceiver Station

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