gsm industrial report

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GLOBAL SYSTEMS FOR MOBILE COMMUNICATIONS

1. BSNL PROFILE

Bharat Sanchar Nigam Ltd. Formed in oct. 2000, is worlds 7th largest telecommunications

company providing comprehensive range of telecom services in India: wire line, CDMA mobile,

GSM mobile, internet, broadband, carrier services. Within a span it has become the one of the

largest public sector unit in India.

BSNL is the only service provider, making focused efforts and planned initiatives to bridge the

rural urban digital divide ICT sector. In fact there is no telecom operator in the country to beat

it reach with its wide network giving services I every nook & corner of country and operates

across India except Delhi & Mumbai.

BSNL cellular service cellone, has more than 20.7 million cellular customers, garnering 24 % of

all mobile users as its subscribers. That means that almost every fourth mobile user in the

country has a BSNL connection. In basic services, BSNL is miles ahead of its rivals, with 35.1

million Basic Phone Subscribers i.e. 85 % share of the subscribers and 92 % share in revenue

terms.

BSNL has set up a world class multi-gigabit, multi-protocol convergent IP infrastructure that

provides convergent services like voice, data and video through the same Backbone and

broadband access network. At present there are 0.6 million Data one broadband customers.

The turnover, nationwide coverage, reach, comprehensive range of the telecom services and the

desire to excel has made BSNL the no. 1 telecom company of India.

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DEPARTMENT OF COMPUTER SCIENCE


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2. INTRODUCTION: THE EVOLUTION OF MOBILE

TELEPHONE SYSTEMS

Cellular is one of the fastest growing and most demanding telecommunications applications.

Today, it represents a continuously increasing percentage of all new telephone subscriptions

around the world. Currently there are more than 45 million cellular subscribers worldwide, and

nearly 50 percent of those subscribers are located in the United States. It is forecasted that

cellular systems using a digital technology will become the universal method of

telecommunications. By the year 2005, forecasters predict that there will be more than 100

million cellular subscribers worldwide. It has even been estimated that some countries may have

more mobile phones than fixed phones by the year 2000 (seeFigure 1).

Figure 1. Cellular Subscriber Growth Worldwide

The concept of cellular service is the use of low-power transmitters where frequencies can be

reused within a geographic area. The idea of cell-based mobile radio service was formulated in

the United States at Bell Labs in the early 1970s. However, the Nordic countries were the first to

introduce cellular services for commercial use with the introduction of the Nordic Mobile

Telephone (NMT) in 1981.

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Cellular systems began in the United States with the release of the advanced mobile phone

service (AMPS) system in 1983. The AMPS standard was adopted by Asia, Latin America, and

Oceanic countries, creating the largest potential market in the world for cellular.

In the early 1980s, most mobile telephone systems were analog rather than digital, like today's

newer systems. One challenge facing analog systems was the inability to handle the growing

capacity needs in a cost-efficient manner. As a result, digital technology was welcomed. The

advantages of digital systems over analog systems include ease of signaling, lower levels of

interference, integration of transmission and switching, and increased ability to meet capacity

demands. Table 1 charts the worldwide development of mobile telephone systems.

Year Mobile System

1981 Nordic Mobile Telephone (NMT) 450

1983 American Mobile Phone System (AMPS)

1985 Total Access Communication System (TACS)

1986 Nordic Mobile Telephony (NMT) 900

1991 American Digital Cellular (ADC)

1991 Global System for Mobile Communication (GSM)

1992 Digital Cellular System (DCS) 1800

1994 Personal Digital Cellular (PDC)

1995 PCS 1900Canada

1996 PCSUnited States

Table 1. The Development of Mobile Telephone Systems

Throughout the evolution of cellular telecommunications, various systems have been developed

without the benefit of standardized specifications. This presented many problems directly related

to compatibility, especially with the development of digital radio technology. The GSM standardis intended to address these problems.

From 1982 to 1985 discussions were held to decide between building an analog or digital system.

After multiple field tests, a digital system was adopted for GSM. The next task was to decide

between a narrow or broadband solution. In May 1987, the narrowband time division multiple

access (TDMA) solution was chosen. A summary of GSM milestones is given below.

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3. GLOBAL SYSTEM

FOR MOBILE

COMMUNICATIONS

(GSM)

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Year Milestone

1982 GSM formed

1986 field test

1987 TDMA chosen as access method

1988 memorandum of understanding signed

1989 validation of GSM system

1990 Pre operation system

1991 commercial system start-up

1992 coverage of larger cities/airports

1993 coverage of main roads

1995 coverage of rural areas


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Figure 2. GSM system BSNL Exchange, Bijapur.

The growth of cellular telephone systems started in the early 1980s, particularly in Europe. The

lack of a technological standardization prompted the European Conference of Postal and

Telecommunications Administrations (CEPT) to create the Groupe Special Mobile (GSM) in

1982 with the objective of developing a standard for a mobile telephone system that could be

used across Europe

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 Radiolinja in Finland. By the end of 1993, over a million

subscribers were using GSM phone networks being operated by 70 carriers across 48 countries.[

The Global System for Mobile communications (GSM: originally from Groupe Spcial

Mobile) is the most popular standard for mobile phones in the world. GSM service is used by

over 2 billion people across more than 212 countries and territories. Its ubiquity makes

international roaming very common between mobile phone operators, enabling subscribers to use

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their phones in many parts of the world. GSM differs significantly from its predecessors in that

both signaling and speech channels are digital call quality, and so is considered a second

generation (2G) mobile phone system. This has also meant that data communication was built

into the system from the 3rd Generation Partnership Project (3GPP).

The GSM logo is used to identify compatible handsets and equipment

The key advantage of GSM systems to consumers has been higher digital voice quality and low

cost alternatives to making calls, such as the Short message service (SMS, also called "text

messaging"). The advantage for network operators has been the ease of deploying equipment

from any vendors that implements the standard. Like other cellular standards, GSM allows

network operators to offer roaming services so that subscribers can use their phones on GSM

networks all over the world.

Newer versions of the standard were backward-compatible with the original GSM phones. For

example, Release '97 of the standard added packet data capabilities, by means of General Packet

Radio Service (GPRS). Release '99 introduced higher speed data transmission using Enhanced

Data Rates for GSM Evolution about GSM.

Radio interface

GSM is a cellular network, which means that mobile phones connect to it by searching for cells

in the immediate vicinity. GSM networks operate in four different frequency ranges. Most GSM

networks operate in the 900 MHz or 1800 MHz bands. Some countries in the Americas

(including Canada and the United States) use the 850 MHz and 1900 MHz bands because the

900 and 1800 MHz frequency bands were already allocated.

The rarer 400 and 450 MHz frequency bands are assigned in some countries, notably

Scandinavia, where these frequencies were previously used for first-generation systems.

In the 900 MHz band the uplink frequency band is 890-915 MHz, and the downlink frequency

band is 935-960 MHz. This 25 MHz bandwidth is subdivided into 124 carrier frequency

channels, each spaced 200 kHz apart. Time division multiplexing is used to allow eight full-rate

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or sixteen half-rate speech channels per radio frequency channel. There are eight radio timeslots

(giving eight burst periods) grouped into what is called a TDMA frame. Half rate channels use

alternate frames in the same timeslot. The channel data rate is 270.833 kbit/s, and the frame

duration is 4.615 ms.

The transmission power in the handset is limited to a maximum of 2 watts in GSM850/900 and 1

watt in GSM1800/1900.

GSM has used a variety of voice codes to squeeze 3.1 kHz audio into between 6 and 13 kbit/s.

Originally, two codecs, named after the types of data channel they were allocated, were used,

called "Full Rate" (13 kbit/s) and "Half Rate" (6 kbit/s). These used a system based upon linear

predictive coding (LPC). In addition to being efficient with bit rates, these codecs also made it

easier to identify more important parts of the audio, allowing the air interface layer to prioritize

and better protect these parts of the signal.

GSM was further enhanced in 1997 with the GSM-EFR codec, a 12.2 kbit/s codec that uses a full

rate channel. Finally, with the development of UMTS, EFR was refactored into a variable-rate

codec called AMR-Narrowband, which is high quality and robust against interference when used

on full rate channels, and less robust but still relatively high quality when used in good radio

conditions on half-rate channels.

There are four different cell sizes in a GSM network - macro, micro, pico and umbrella cells. The

coverage area of each cell varies according to the implementation environment. Macro cells can

be regarded as cells where the base station antenna is installed on a mast or a building above

average roof top level. Micro cells are cells whose antenna height is under average roof top level;

they are typically used in urban areas. Picocells are small cells whose coverage diameter is a few

dozen meters; they are mainly used indoors. Umbrella cells are used to cover shadowed regions

of smaller cells and fill in gaps in coverage between those cells.

Cell horizontal radius varies depending on antenna height, antenna gain and propagationconditions from a couple of hundred meters to several tens of kilometers. The longest distance

the GSM specification supports in practical use is 35 km or 22 miles. There are also several

implementations of the concept of an extended cell, where the cell radius could be double or

even more, depending on the antenna system, the type of terrain and the timing advance.

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Indoor coverage is also supported by GSM and may be achieved by using an indoor picocell base

station, or an indoor repeater with distributed indoor antennas fed through power splitters, to

deliver the radio signals from an antenna outdoors to the separate indoor distributed antenna

system. These are typically deployed when a lot of call capacity is needed indoors, for example

in shopping centers or airports. However, this is not a prerequisite, since indoor coverage is also

provided by in-building penetration of the radio signals from nearby cells.

The modulation used in GSM is Gaussian minimum-shift keying (GMSK), a kind of continuous-

phase frequency shift keying. In GMSK, the signal to be modulated onto the carrier is first

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Multiple Access TDMA/FDMA/FDAUplink frequency(mobile to base) 890-915 MhzDownlink frequency(base to mobile ) 935-960 MhzChannel Bandwidth 200 KhzNumber of channels 124Channels/carrier 8(full rate),16(half rate)Frame duration 4.6msInterleaving duration 40msModulation GMSK Speech coding method RPE-LTE convolutionSpeech coder bit rate 13kb/s (full rate)Associated control channel Extra frameHandoff scheme Mobile assistedMobile station power levels 0.8, 2,58 w


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smoothed with a Gaussian low-pass filter prior to being fed to a frequency modulator, which

greatly reduces the interference to neighboring channels (adjacent channel interference).

DETAILS:

A nearby GSM handset is usually the source of the "dit dit dit, dit dit dit, dit dit dit" signal thatcan be heard from time to time on home stereo systems, televisions, computers, and personal

music devices. When these audio devices are in the near field of the GSM handset, the radio

signal is strong enough that the solid state amplifiers in the audio chain function as a detector.

The clicking noise itself represents the power bursts that carry the TDMA signal. These signals

have been known to interfere with other electronic devices, such as car stereos and portable

audio players. This is a form of RFI, and could be mitigated or eliminated by use of additional

shielding and/or bypass capacitors in these audio devices. However, the increased cost of doing

so is difficult for a designer to justify.

4. THE GSM NETWORK

GSM provides recommendations, not requirements. The GSM specifications define the functions

and interface requirements in detail but do not address the hardware. The reason for this is to

limit the designers as little as possible but still to make it possible for the operators to buy

equipment from different suppliers. The GSM network is divided into four major systems: the

(1) Switching system (SS), (2) The base station system (BSS), (3) Operation and support system

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(OSS) and (4) Mobile station. The basic GSM network elements are shown in Figure 3.

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Figure 3. GSM Network Elements.

4.1 The Switching System

The switching system (SS) is responsible for performing call processing and subscriber-related

functions. The switching system includes the following functional units.

Home location registers (HLR) The HLR is a database used for storage and

management of subscriptions. The HLR is considered the most important database, as it

stores permanent data about subscribers, including a subscriber's service profile, location

information, and activity status. When an individual buys a subscription from one of thePCS operators, he or she is registered in the HLR of that operator.

Mobile services switching center (MSC)The MSC performs the telephony switching

functions of the system. It controls calls to and from other telephone and data systems. It

also performs such functions as toll ticketing, network interfacing, common channel

signaling, and others.

Visitor location registers (VLR) The VLR is a database that contains temporary

information about subscribers that is needed by the MSC in order to service visiting

subscribers. The VLR is always integrated with the MSC. When a mobile station roams

into a new MSC area, the VLR connected to that MSC will request data about the mobile

station from the HLR. Later, if the mobile station makes a call, the VLR will have the

information needed for call setup without having to interrogate the HLR each time.

Authentication center (AUC)A unit called the AUC provides authentication and

encryption parameters that verify the user's identity and ensure the confidentiality of each

call. The AUC protects network operators from different types of fraud found in today's

cellular world.

equipment identity register (EIR)The EIR is a database that contains information

about the identity of mobile equipment that prevents calls from stolen, unauthorized, or

defective mobile stations. The AUC and EIR are implemented as stand-alone nodes or as

a combined AUC/EIR nod

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4.2 The Base Station System (BSS)

Figure 4. Motorola Base Station System (BSS) BSNL Exchange, Bijapur.

All radio-related functions are performed in the BSS, which consists of base station controllers

(BSCs) and the base transceiver stations (BTSs).

Base Station Controllers (BSC) The BSC provides all the control functions and

physical links between the MSC and BTS. It is a high-capacity switch that provides

functions such as handover, cell configuration data, and control of radio frequency (RF)

power levels in base transceiver stations. A number of BSCs are served by an MSC.

Base Transceiver Station (BTS)The BTS handles the radio interface to the mobile

station. The BTS is the radio equipment (transceivers and antennas) needed to service

each cell in the network. A group of BTSs are controlled by a BSC.

Base Transceiver Station (BTS)

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Figure 5. Base Transceiver Station BSNL Exchange, Bijapur

A BTS is a network component that serves one cell and is controlled by a BSC. BTS is typicallyable to handle three to five radio carries, carrying between 24 and 40 simultaneous

communication. Reducing the BTS volume is important to keeping down the cost of the cell

sites.

An important component of the BSS that is considered in the GSM architecture as a part

of the BTS is the Transcoder/Rate Adapter Unit (TRAU). The TRAU is the equipment in which

coding and decoding is carried out as well as rate adoption in case of data. Although the

specifications consider the TRAU as a subpart of the BTS, it can be sited away from the BTS (at

MSC), and even between the BSC and the MSC.

The interface between the MSC and the BSS is a standardized SS7 interface (A-interface) that, as

stated before, is fully defined in the GSM recommendations. This allows the system operator to

purchase switching equipment from one supplier and radio equipment and the controller from

another. The interface between the BSC and a remote BTS likewise is a standard the A-bis. InBEC, BAGALKOT



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splitting the BSS functions between BTS and BSC, the main principle was that only such

functions that had to reside close to the radio transmitters/receivers should be placed in BTS.

This will also help reduce the complexity of the BTS.

Based on the aforementioned argument, some of the functions that were placed in the

BTS areas are as follows.

Broadcast control and common Control channel (BCCH/CCCH) message scheduling has

to be made by BTS as it has the exact knowledge of BCCH/CCCH timing (not known by

BSC). This includes the scheduling of paging message on paging sub channels.

Random access detection has to be made by BTS, which in turn sends a message to BSC.

Subsequent channel assignment is made by BSC.

Timing advance is determined by BTS. It is also signaled to MS by the BTS except after

random access when it is reported to BSC for inclusion in the assignment message.

Uplink radio channel measurement has to be made by BTS.

The BTS has to detect the handover access burst sent by MS.

Error protection channel coding/decoding and encryption of the radio channel has to be

done in BTS.

Layer 2 of the radio interface (LAPDm) has to be terminated in BTS.

Based on this discussion, we shall first provide of BTS; BTS-BSC configuration; the use of a

transcoder, which for all practical purpose can be considered to be part of BTS; and lastly;

functions of BSC.

Functions of BTS

As stated, the primary responsibility of the BTS is to transmit and receive radio signals from a

mobile unit over an air interface. To perform this function completely, the signals are encoded,

encrypted, multiplexed, modulated, and then fed to the antenna system at the cell site. Trans-

coding to bring 13-kbps speech to a standard data rate of 16 kbps and then combining four of

these signals to 64 kbps is essentially a part of BTS, though; it can be done at BSC or at MSC.

The voice communication can be either at a full or half rate over logical speech channel. In order

to keep the mobile synchronized, BTS transmits frequency and time synchronization signals over

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frequency correction channel (FCCH and BCCH logical channels. The received signal from the

mobile is decoded, decrypted, and equalized for channel impairments. Since the GSM signals are

supposed to be frequency hopped, the control within the cell is actually exercised such that no

two subscribers hop to the same frequency. Thus it is the responsibility of the BTS to make sure

that hopping signals are kept orthogonal within the BSC serving area. A list of functions

performed by BTS is as follows.

Encodes, encrypts, multiplexes, modulates and feeds the RF signals to the

antenna.

Trans-coding and rate adaptation.

Time and frequency synchronization signals transmitted from BTS.

Each BTS serves a single cell.

Voice communication through full rate or half rate(future date) speech channel.

Received signal from mobile is decoded, decrypted and equalized before

demodulation.

Frequency hopping controlled such that no two MSs in the same BSC area are

hopped together.

Random access detection.

Timing advance.

Uplink radio channel measurements.

Random access detection is made by BTS, which then sends the message to BSC. The channel

subsequent assignment is made by BSC. Timing advance is determined by BTS. BTS signals the

mobile for proper timing adjustment. Uplink radio channel measurement corresponding to the

downlink measurements made by MS has to be made by BTS.

BTS-BSC Configurations

There are several BTS-BSC configurations: single site; single cell; single site; multicell; and

multisite, multicell. These configurations are chosen based on the rular or urban application.

These configurations make the GSM system economical since the operation has options to adapt

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the best layout based on the traffic requirement. Thus, in some sense, system optimization is

possible by the proper choice of the configuration. These include omni directional rural

configuration where the BSC and BTS are on the same site; chain and multidrop loop

configuration in which several BTSs are controlled by a single remote BSC with a chain or ring

connection topology; rural star configuration in which several BTSs are connected by individual

lines to the same BSC; and sectorized urban configuration in which three BTSs share the same

site amd are controlled by either a collocated or remote BSC.

In rural areas, most BSs are installed to provide maximum coverage rather then maximum

capacity. High levels of traffic are not problems in those areas. The largest coverage area from

the radio point-of-view (30 KM to 70 KM) can only provide a fraction of traffic for a single

transceiver. Therefore, it was necessary to come up with a low-cost and low-complexity

configuration for the rural areas. The MSC in this case would still be connected via the A-

interface not to the BSC but to the BSS consisting of a single or multiple cells. If the cells are not

collocated, the BSS will be split between BSC and BTS where BSC will then be connected to

several BTSs. between BSC and BTS is the A-bis interface. For high-traffic surroundings in

urban areas, MSC can be connected to a number of BSSs via A-interface. Some of the BSSs are

multicell (sectored) sites.

Transcoder

Depending on the relative costs of a transmission plant for a particular cellular operator,

there may be some benefit, for larger cells and certain network topologies, in having the

transcoder either at the BTS, BSC or MSC location. If the transcoder is located at MSC, they are

still considered functionally a part of the BSS. This approach allows for the maximum of

flexibility and innovation in optimizing the transmission between MSC and BTS.

The transcoder is the device that takes 13-Kbps speech or 3.6/6/12-Kbps data multiplexes and

four of them to convert into standard 64-Kbps data. First, the 13 Kbps or the data at 3.6/6/12

Kbps are brought up to the level of 16 Kpbs by inserting additional synchronizing data to make

up the difference between a 13-Kbps speech or lower rate data, and then four of them are

combined in the transcoder to provide 64 Kpbs channel within the BSS. Four traffic channels can

then be multiplexed on one 64-Kpbs circuit. Thus, the TRAU output data rate is 64 Kpbs. Then,

up to 30 such 64-Kpbs channels are multiplexed onto a 2.048 Mpbs if a CEPT1 channel is

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provided on the A-bis interface. This channel can carry up to 120-(16x 120) traffic and control

signals. Since the data rate to the PSTN is normally at 2 Mbps, which is the result of combining

30-Kbps by 64-Kbph channels, or 120- Kbps by 16-Kpbs channels.

Base Station Controllers

Figure 6.Base Station Controller BSNL Exchange, Bijapur

The BSC, is connected to the MSC on one side and to the BTS on the other. The BSC performs

the Radio Resource (RR) management for the cells under its control. It assigns and release

frequencies and timeslots for all MSs in its own area. The BSC performs the intercell handover

for MSs moving between BTS in its control. It also reallocates frequencies to the BTSs in its area

to meet locally heavy demands during peak hours or on special events. The BSC controls the

power transmission of both BSSs and MSs in its area. The minimum power level for a mobile

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unit is broadcast over the BCCH. The BSC provides the time and frequency synchronization

reference signals broadcast by its BTSs. The BSC also measures the time delay of received MS

signals relative to the BTS clock. If the received MS signal is not centered in its assigned

timeslot at the BTS, The BSC can direct the BTS to notify the MS to advance the timing such

that proper synchronization takes place. The functions of BSC are as follows.

RR management for BTSs under its control;

Inter-cell handover;

Reallocation of frequencies among BTSs;

Power management of BTSs;

Time and frequency synchronization signals to BTSs;

Time delay measurement of the received signals from MSs with respect to BTS

clock;

Controls frequency hopping;

Performs traffic concentration to reduce the number of lines from BSC to MSC

and BTSs;

Provides interface to the Operations and Management for BSS.

The BSC controls the frequency hopping of all the BTSs and MSs in its area. It establishes the

hopping sequence for each BTS and directs the BTS to inform the MSs under its control of the

assigned sequence.

The BSC may also perform traffic concentration to reduce the number of transmission lines from

the BSC to its BTSs,

4.3 The Operation and Support System

The operations and maintenance center (OMC) is connected to all equipment in the switching

system and to the BSC. The implementation of OMC is called the operation and support system

(OSS). The OSS is the functional entity from which the network operator monitors and controls

the system. The purpose of OSS is to offer the customer cost-effective support for centralized,

regional and local operational and maintenance activities that are required for a GSM network.

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An important function of OSS is to provide a network overview and support the maintenance

activities of different operation and maintenance organizations.

4.4 Mobile Station

This may be a standalone piece of equipment for certain services or support the connection of

external terminals. The MS consists of the Mobile Equipment (ME) and a Subscriber Identity

Module (SIM).

The ME is uniquely identified by the International Mobile Equipment Identity (IMEI), but it

need not be personally assigned to one subscriber, The SIM which is a smart card provides

personal mobility and the user can access the subscriber services. The subscriber can operate on

any terminal just by inserting the SIM card in that GSM terminal. SIM card contains the

International Mobile Subscriber Identity (IMSI) used to identify the subscriber to the system, a

secret key for authentication and other security informations. SIM card may be protected against

unauthorized use by a password.

Functions of MS

The primary functions of MS are to transmit and receive voice and data over the air interface of

the GSM system. MS performs the signal processing function of digitizing, encoding, error

protecting, encrypting, and modulating the transmitted signals. It also performs the inverse

functions on the received signals from the BS. A list of relevant functions includes the following.

Voice and data transmission

Frequency and time synchronization

Monitoring of power and signal quality of the surrounding cells for optimum handover.

Provision of location updates.

Equalization of multipath distortion

Display of short message up to 160 characters long

Timing advance.

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Additional Functional Elements

Other functional elements shown inFigure 2 are as follows:

Message center (MXE)The MXE is a node that provides integrated voice, fax, and

data messaging. Specifically, the MXE handles short message service, cell broadcast,voice mail, fax mail, e-mail, and notification.

Mobile service node (MSN)The MSN is the node that handles the mobile intelligent

network (IN) services.

Gateway mobile services switching center (GMSC)A gateway is a node used to

interconnect two networks. The gateway is often implemented in an MSC. The MSC is

then referred to as the GMSC.

GSM interworking unit (GIWU)The GIWU consists of both hardware and softwarethat provides an interface to various networks for data communications. Through the

GIWU, users can alternate between speech and data during the same call. The GIWU

hardware equipment is physically located at the MSC/VLR.

5. GSM NETWORK AREAS

The GSM network is made up of geographic areas. As shown inFigure 7, these areas include

cells, location areas (LAs), MSC/VLR service areas, and public land mobile network (PLMN)

areas.

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Figure 7: Network Areas

The cell is the area given radio coverage by one base transceiver station. The GSM network

identifies each cell via the cell global identity (CGI) number assigned to each cell. The location

area is a group of cells. It is the area in which the subscriber is paged. Each LA is served by one

or more base station controllers, yet only by a single MSC (seeFigure 8). Each LA is assigned a

location area identity (LAI) number.

Figure 8: Location Areas

An MSC/VLR service area represents the part of the GSM network that is covered by one MSC

and which is reachable, as it is registered in the VLR of the MSC (see Figure 9).

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Figure 9. MSC/VLR Service Areas

The PLMN service area is an area served by one network operator (see Figure 10).

Figure 10. PLMN Service Area

6. GSM SPECIFICATIONS

Before looking at the GSM specifications, it is important to understand the following basic

terms:

Bandwidththe range of a channel's limits; the broader the bandwidth, the faster data

can be sent

Bits per second (bps)a single on-off pulse of data; eight bits are equivalent to one byte

Frequencythe number of cycles per unit of time; frequency is measured in hertz (Hz)

Kilo (k)kilo is the designation for 1,000; the abbreviation kbps represents 1,000 bits

per second

Megahertz (MHz)1,000,000 hertz (cycles per second)

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Milliseconds (ms)one-thousandth of a second

Watt (W)a measure of power of a transmitter

Specifications for different personal communication services (PCS) systems vary among the

different PCS networks. Listed below is a description of the specifications and characteristics forGSM.

Frequency band The frequency range specified for GSM is 1,850 to 1,990 MHz

(mobile station to base station).

Duplex distanceThe 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 separationThe separation between adjacent carrier frequencies. In GSM, thisis 200 kHz.

ModulationModulation 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 rateGSM is a digital system with an over-the-air bit rate of 270 kbps.

Access methodGSM 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 coderGSM 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.

The signal passes through this filter, leaving behind a residual signal. Speech is encoded

at 13 kbps.

7. SUBSCRIBER IDENTITY MODULE

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Figure 11. A SIM for BSNL (India)

One of the key features of GSM is the Subscriber Identity Module (SIM), commonly known as a

SIM card. The SIM is a detachable smart card containing the user's subscription information and

phonebook. This allows the user to retain his or her information after switching handsets.

The subscriber is identified in the system when he inserts the SIM card in the mobile equipment.

This provides an enormous amount of flexibility to the subscribers since they can now use any

GSM-specified mobile equipment. Thus with a SIM card the idea of Personalize the equipment

currently in use and the respective information used by the network (location information) needs

to be updated. The smart card SIM is portable between Mobile Equipment (ME) units. The user

only needs to take his smart card on a trip. He can then rent a ME unit at the destination, even in

another country, and insert his own SIM. Any calls he makes will be charged to his home GSM

account. Also, the GSM system will be able to reach him at the ME unit he is currently using. It

is expected that, in the future, rental cars will come equipped with GSM MEs and that many

hotels will provide handheld MEs for use by their guests. When the users ME is being serviced,

the shop will give another for temporary use with ones own SIM. The detailed functions and

contents of the SIM card are as follows.

Removable plastic card or the SIM module;

Unique mobile subscriber ID through IMSI and ISDN numbers;

PIN;

Authentication key Ki and A3, A5, and A8 algorithms.

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The SIM is a removable SC, the size of a credit card, and contains an integrated circuit chip

with a microprocessor, random access memory (RAM), and read only memory (ROM). It is

inserted in the MS unit by the subscriber when he or she wants to use the MS to make or

receive a call. As stated, a SIM also comes in a modular from that can be mounted in the

subscribers equipment.

The SIM contains all subscriber-specific data stored on the MS side. The SIM is basically a

smart card, but it can assume the shape of an ISO-sized card or a small component, both

having the same standardized electrical and functional interface with a ME. It contains few

functions; they relate to security features (such as authentication) and the storage of user

specific data, like location information. The SIM memory contains a unique IMSI

(subscription-related data) number that is necessary to identify the subscriber to the system

when he attempts access to make or receive a call. It also contains a unique MSISDN, which

is the unique mobile identification for PSTN/ISDN calls to the mobile. The SIM also

contains various temporary subscriber related data that changes from time to time. The

storage function of SIM is very important, especially when it is removed from ME.

When a mobile subscriber wants to use the system, he or she mounts their SIM card

and provide their Personal Identification Number (PIN), which is compared with a PIN

stored within the SIM. If the user enters three incorrect PIN codes, the SIM is disabled. The

PIN can also be permanently bypassed by the service provider if requested by the subscriber.

Disabling the PIN code simplifies the call setup but reduces the protection of the users

account in the event of a stolen SIM.

User authentication to the network is provided by the MS/SIM sending a unique response to

a random number challenge from the GSM system. The SIM contains an authentication

parameter Ki uniquely assigned to the subscriber at the very beginning of the service that is

also kept at the AUC and Algorithm A3 to calculate the response to the network challenge.

Algorithm A8 generates the encryption key and Algorithm A5 the actual encryption.

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8. GSM SUBSCRIBER SERVICES

There are two basic types of services offered through GSM: telephony (also referred to as

teleservices) and data (also referred to as bearer services). Telephony services are mainly voice

services that provide subscribers with the complete capability (including necessary terminalequipment) to communicate with other subscribers. Data services provide the capacity necessary

to transmit appropriate data signals between two access points creating an interface to the

network. In addition to normal telephony and emergency calling, the following subscriber

services are supported by GSM:

Dual-tone multi frequency (DTMF)DTMF is a tone signaling scheme often used for

various control purposes via the telephone network, such as remote control of an

answering machine. GSM supports full-originating DTMF.

Facsimile group III GSM supports CCITT Group 3 facsimile. As standard fax

machines are designed to be connected to a telephone using analog signals, a special fax

converter connected to the exchange is used in the GSM system. This enables a GSM

connected fax to communicate with any analog fax in the network.

Short message servicesA convenient facility of the GSM network is the short message

service. A message consisting of a maximum of

160 alphanumeric characters can be sent to or from a mobile station. This service can be viewed

as an advanced form of alphanumeric paging with a number of advantages. If the subscriber's

mobile unit is powered off or has left the coverage area, the message is stored and offered back

to the subscriber when the mobile is powered on or has reentered the coverage area of the

network. This function ensures that the message will be received.

Cell broadcastA variation of the short message service is the cell broadcast facility. A

message of a maximum of 93 characters can be broadcast to all mobile subscribers in a

certain geographic area. Typical applications include traffic congestion warnings and

reports on accidents.

Voice mailThis service is actually an answering machine within the network, which is

controlled by the subscriber. Calls can be forwarded to the subscriber's voice-mail box

and the subscriber checks for messages via a personal security code.

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Fax mailWith this service, the subscriber can receive fax messages at any fax

machine. The messages are stored in a service center from which they can be retrieved by

the subscriber via a personal security code to the desired fax number.

9. SUPPLEMENTARY SERVICES

GSM supports a comprehensive set of supplementary services that can complement and support

both telephony and data services. Supplementary services are defined by GSM and are

characterized as revenue-generating features. A partial listing of supplementary services follows.

Call forwarding This service gives the subscriber the ability to forward incoming calls

to another number if the called mobile unit is not reachable, if it is busy, if there is no

reply, or if call forwarding is allowed unconditionally.

Barring of outgoing callsThis service makes it possible for a mobile subscriber to

prevent all outgoing calls.

Barring of incoming callsThis function allows the subscriber to prevent incoming

calls. The following two conditions for incoming call barring exist: baring of all

incoming calls and barring of incoming calls when roaming outside the home PLMN.

Advice of charge (AoC)The AoC service provides the mobile subscriber with anestimate of the call charges. There are two types of AoC information: one that provides

the subscriber with an estimate of the bill and one that can be used for immediate

charging purposes. AoC for data calls is provided on the basis of time measurements.

Call holdThis service enables the subscriber to interrupt an ongoing call and then

subsequently reestablish the call. The call hold service is only applicable to normal

telephony.

Call waitingThis service enables the mobile subscriber to be notified of an incoming

call during a conversation. The subscriber can answer, reject, or ignore the incoming call.

Call waiting is applicable to all GSM telecommunications services using a circuit-

switched connection.

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Multiparty serviceThe multiparty service enables a mobile subscriber to establish a

multiparty conversationthat is, a simultaneous conversation between three and six

subscribers. This service is only applicable to normal telephony.

Calling line identification presentation/restrictionThese services supply the called

party with the integrated services digital network (ISDN) number of the calling party.

The restriction service enables the calling party to restrict the presentation. The restriction

overrides the presentation.

Closed user groups (CUGs)CUGs are generally comparable to a PBX. They are a

group of subscribers who are capable of only calling themselves and certain numbers.

10. EXPERIENCE IN BSNL

It was a great learning curve at BSNL, Bijapur undergoing my M.Tech industrial training. The

training was full of all technicalities loaded with all relevant information and knowledge which

would be competent enough in the current knowledge market.

The Training;

Got me thorough insight into Industry Standard.

I was provided with the printed material developed by well established experts and

market leaders in GSM market.

Learnt and interacted with experts.

It was a Practical learning based training program.

Got hands on demonstration of latest technologies.

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CONCLUSION

This Practical Training has given me an opportunity to know about various technologies working

behind in todays advanced world of telecommunication .I have learned about different units in

BSNL exchange like C-DOT, E10B,OCB, Mobile (GSM), MDF, Power Plant and Broadband.

I tried to group as much as I could, which switched my knowledge and logic.

As a student of computer science I learned GSM which is mainly concerned with my focus area.

I am very grateful to those persons who helped directly &indirectly in the successful

completion of this practical training and this will surely be fruitful in future.

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REFERENCES

Wikipedia, the free encyclopedia

www.bsnl.co.in

www.google.com

www.dataone.in

www.gsmdata.com

www.gsmworld.com

BSNL Manuals, Bijapur
http://www.bsnl.co.in/http://www.google.com/http://www.dataone.in/http://www.gsmdata.com/http://www.gsmworld.com/http://www.google.com/http://www.dataone.in/http://www.gsmdata.com/http://www.gsmworld.com/http://www.bsnl.co.in/

gsm industrial report

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