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    THE INSTITUTION OF ENGINEERS ( INDIA )

    PROJECT REPORT

    ON

    G.S.M

    ( GLOBAL SERVICE FOR MOBILE COMMUNICATION )

    UNDER GUIDANCE OF

    Dr. J S SOHAL (FIE)

    SUBMITTED BY

    BANARASEE LAL(Mem. No. :- ST 398118-0(Ref. EEA/39/ST3981180)

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    CERTIFICATE

    I certify that the project work done by me is original and has

    not been submitted to any other institution for fulfillment of the

    requirement of a course of study.

    ( BANARASEE LAL )

    COUNTER SIGN.

    ( J.S SOHAL , FIE )

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    INDEX

    Sheet No.

    Synopsis 1

    FINAL PROJECT REPORT

    1. Title of project 4

    2. Objective of study 4

    3. Methodology of the study 4

    4. Statement of problem 4

    5. DiscriptionUnit 1. ISDN in India 5

    Unit 2. Administrative system 6

    Unit 3. History 7

    Unit 4.ISDN Features and functions 9

    Unit 5.ISDN technical fundamentals

    5.5.1. Basic ISDN Installation requirment 11

    5.5.2. ISDN reference points 13

    5.5.3. B,D,and H channels 14

    5.5.4. BRI and PRI services 16

    5.5.5. ISDN frames 185.5.6. ISDN Protocol (Layer) 19

    Unit 6. Services provided by BSNL on ISDN 23

    Unit 7. Commercial aspect of interface with customers 25

    Unit 8. ISDN service enhancements 29

    Unit 9. ISDN competitor technologies 31

    6. Final results 35

    7. Conclusion 35

    8. Scope of future study 35

    9. References 3610.Appendix A 37

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    SYNOPSIS

    1. TITLE OF PROJECT:-

    Mobile Communication using GSM Technology; BSNL - A Case Study.

    2. OBJECTIVES OF THE STUDY:-

    To have complete familiarisation with the concepts of rapidlydeveloping field of mobile communication using GSM technology,

    which in the past 10 years not only have increased 40 fold butalso changed the life style of people & the way businesses weredone, thus resulting in complete telecom revolution.

    3. RATIONALE FOR THE STUDY:-

    (a) Over the years Phone on the move (mobile), has become anabsolute necessity than a mere luxury.

    (b) It has become an economically viable option for mostsection of the society.

    (c) Have resulted in high density of users who remainconnected anytime anywhere.

    (d) Innovative value added services made it the most popularcommunication system.

    (e) Being a user friendly system, more and more people aregetting attracted towards it day by day.

    So this study project is undertaken in order to contribute asmuch as possible towards the telecom revolution and be a partof the growth story of boosting economy.

    4. DETAILED METHODOLOGY USED FOR CARRYING OUT THESTUDY:-

    (a) Visit to BTS (Base Transceiver Station) at BRS Nagar,Ludhiana to see the antenna structure and the equipmentswith facilities of uninterrupted power supply.

    (b) Visit to BSC (Base Station Controller) at BN Chowk,Ludhiana to get a first hand experience on the basics of

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    radio related functions and MS handover. Study themanuals available on site.

    (c) Visit the XCDR (Transcoder) system at BN Chowk, Ludhianato understand its operation and maintenance.

    (d)Visit to MSC (Mobile service switching centre) at Sec-34Chandigarh to get a first hand account of functioning ofdifferent essential systems. E.g. HLR (Home LocationRegister), AuC (Authentication Register), VLR (VisitorLocation register), EIR (Equipment Identification Register).Study the manuals available on site.

    5. THE EXPECTED CONTRIBUTION FROM THE STUDY:-

    a) Dissemination through IE(I) centers practical and technical

    realities described in the project will help the students ofcommunication engineering branches.

    b) This can be used as handy guide book for BSNL employees/perspective BSNL employees and engineers aspiring topursue a career in the field of mobile communications.

    6. LIST OF ACTIVITIES TO BE CARRIED OUT TO COMPLETETHE PROJECT ( WITH THE HELP OF A BAR CHART SHOWINGTHE TIME SCHEDULE ) :-

    7. PLACES/LAB/EQUIPMENT AND TOOLS REQUIRED ANDPLANNING OF ARRANGEMENT:-

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    ( a ) BSNL BTS at BRS Nagar, Ludhiana

    ( b ) BSNL BSC at Bharat Nagar Chowk, Ludhiana

    ( c ) BSNL MSC at Sec-34, Chandigarh.

    8. PROBLEMS ENVISAGED IN CARRYING OUT THE PROJECT,IF ANY:-

    NIL

    S-4

    FINAL PROJECT REPORT

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    1. TITLE OF PROJECT:-

    Mobile Communication using GSM Technology; BSNL - A Case Study.

    2. OBJECTIVES OF THE STUDY:-

    To have complete familiarisation with the concepts of rapidlydeveloping field of mobile communication using GSM technology,which in the past 10 years not only have increased 40 fold butalso changed the life style of people & the way businesses weredone, thus resulting in complete telecom revolution.

    3. METHODOLOGY OF THE STUDY :-

    (A) Visit to BTS (Base Transceiver Station) at BRS Nagar,Ludhiana to see the antenna structure and the equipmentswith facilities of uninterrupted power supply.

    (B)Visit to BSC (Base Station Controller) at BN Chowk,Ludhiana to get a first hand experience on the basics ofradio related functions and MS handover. Study themanuals available on site.

    (C)Visit the XCDR (Transcoder) system at BN Chowk, Ludhianato understand its operation and maintenance.

    (D)Visit to MSC (Mobile service switching centre) at Sec-34Chandigarh to get a first hand account of functioning of

    different essential systems. E.g. HLR (Home LocationRegister), AuC (Authentication Register), VLR (VisitorLocation register), EIR (Equipment Identification Register).Study the manuals available on site.

    4.STATEMENT OF PROBLEM:-

    To have comprehensive technical information about

    various GSM services of BSNL to Indian customers.

    S-5

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    S-6

    (Unit-1)

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    ADMINISTRATIVE SET UP in BSNL

    GM

    DGM(CCN) DGM(CMTS)

    DE(CCN) DE(SWITCH) DE(OUTDOOR)

    SDE ( 2 TO 3 ) SDE(SWITCH) SDE(OUTDOOR)

    JTO ( 2 TO 3) JTO(SWITCH) JTO(OUTDOOR)

    TTA (5 TO 6 ) TTA(2 TO 3) TTA(8 TO 10)

    SFs SFs

    SFs

    HERE

    GM-General Manager

    DGM-Depty GM

    DE-Divisional Engineer

    SDE-Sub Divisional Engineer

    JTO-Junior Telecom Officer

    TTA-Telecom Technical Assistant

    SFs -SUPPORTING STAFF(Telephone Mechanics,Telecom Office assistant,Telecom

    Operator,Clerks etc

    S-7

    (Unit-2)

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    S-8

    History of Mobile Communication

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    Wireless communication was a magic to our ancestors but Marconi could initiate it

    with his wireless telegraph in 1895.Wireless Communication can be classified into three

    eras.

    Pioneer Era (Till 1920)

    Pre Cellular Era(1920-1970)

    Cellular Era (beyond 1970)

    History - Pioneer Era (Till 1920) :-

    In 1946 f irst commercial mobile

    telephone system was launched by BELL in St.

    Louis, USA. Few lucky customers were getting

    the services .Early mobile systems were usingsingle high power transmitters with analog

    Frequency Modulat ion techniques to give

    coverage up to about 50 miles. Few customers

    on ly could get the serv ice due to severe

    constraints of bandwidth.

    History - CELLULAR ERA

    To overcome the constraints of bandwidth scarcity and to give coverage to larger

    sections, BELL lab introduced the principle of Cellular concept. By frequency reuse

    technique this method provides for better coverage, better utility of available frequency

    spectrum and reduced transmitter power. But the established calls are to be handed over

    Between base stations while the phones are on move

    Even though US based BELL lab introduced cellular principle, the Nordic countries were the

    first to introduce cellular services for commercial use with the introduction of the Nordic

    Mobile Telephone (NMT) in 1981.

    S-9

    History - First Generation Systems

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    All these systems were analog systems, using FDMA. They are also known as First-

    Generation(1G)systems

    Different systems came into use based on cellular principle. They are listed below.

    Year Mobile System

    1981 Nordic Mobile Telephone(NMT)4501982 American Mobile Phone System(AMPS)

    1985 Total Access Communication System(TACS)

    1986 Nordic Mobile Telephony(NMT)900

    History of Mobile Communication

    To overcome the difficulties of 1G, digital technology was chosen by most of the

    countries and a new era started.

    Advantages

    Improved Spectral Utilization achieved by using advanced Modulation Techniques.

    Lower bit rate voice coding enabled more users getting the services simultaneously.

    Reduction of overhead in signaling paved way for capacity enhancement.

    Good source and channel coding techniques make the signal more robust to Interference.

    New services like SMS are included.

    Improved efficiency of access and hand-off control is achieved.

    History of Mobile Communication

    Name of the systems Country

    North American Digital Cellular-NADC

    North America

    GSM-Global System for Mobilecommunication

    European Countries and Internationalapplications

    JDC - Japanese Digital Cellular Japan

    Cordless Telephone2 UK

    Digital European CordlessTelephone(DECT)

    European countries

    S-10

    History - Milestones of GSM

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    1982-Confederation of European Post and Telegraph (CEPT) establishes Group

    Special mobile

    1985-Adoption of list of recommendation to be generated by the group.

    1986-Different field tests for radio technique for the common air interface.

    1987-TDMA chosen as Access Standard. MoU signed between 12 operators.

    1988-Validation of system.

    1989- Responsibility taken up ETSI

    1990-First GSM specification released

    1991-First commercial GSM system launched.

    History - Frequency Range of GSM

    GSM works on 4 different frequency ranges with FDMA-TDMA and FDD.They are as

    follows

    SystemP-GSM

    (Primary)

    E-GSM

    (Extended)GSM 1800 GSM 1900

    Freq Uplink 890-915MHz 880-915MHz 1710-1785Mhz 1850-1910MHz

    Freq Downlink 935-960MHz 925-960MHz 1805-1880Mhz 1930-1990MHz

    S-11

    (Unit-3)

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    S-12

    INTRODUCTION

    Mobile communications have made phones to move, breaking the convention that

    phones are attached to places but not the persons.It provides all facilities like voice and

    data.

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    OBJECTIVES:-

    Any time Anywhere

    Mobility & Roaming

    High capacity & subscriber. density

    Efficient use of radio spectrum

    Seamless Network Architecture

    Low cost

    Innovative Services

    Standard Interfaces

    ELECTROMAGNETIC WAVE:-

    The transmission and reception of information using ElectroMagnetic(EM) waves is

    known as Radio or Wireless communication. An EM wave, consists of an Electrical

    component and a Magnetic component.The directions of the Electric component, the

    Magnetic component and Propagation are mutually perpendicular to each other.

    POLARIZATION:-

    The direction of the Electrical component is known as the Polarization of an EM

    wave.In Plane polarization, the direction of the 'E' component does NOT change whereas in

    Circular polarization, the direction of the 'E' component changes. Plane polarization is

    generally used in terrestrial radio systems and Circular in Satellite

    communications.Nowadays, dual polarized antennae are a common sight.Polarization helps

    in discrimination and augmenting the capacity of a radio system as well.

    S-13

    Horizontal Polarisation:-

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    In a Horizontally polarised EM wave, the direction of Electric field is parallel to the ground

    surface

    Vertical Polarisation:-

    In a Vertically polarised EM wave, the direction of Electric field is perpendicular to the

    ground surface.

    S-14

    ElectroMagnetic Spectrum:-

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    ANTENNA:

    Antennas transform wire-

    propagated waves into space-propagated

    waves. They receive electromagnetic

    waves and pass them onto a receiver or

    they transmit electromagnetic waves,

    which have been produced by a

    transmitter.All the features of passive

    antennas can be applied for reception and

    transmission alike (reciprocality). On one

    side RF cable is connected and the other

    side it is the environment, therefore the

    surroundings of the antenna have a strong

    inf luence on the antenna's electrical

    features.

    S-15

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    The Principle of an antenna:-

    a) A transmitter sends a high frequency wave into a co-

    axial cable. A pulsing electrical field is created between the

    wi res, whi ch cannot free itself from the cabl e

    b) The end of the cable is bent open. The field lines become

    longer and are orthogonal to the wires.

    c) The cable is bent open at right angles. The field lines

    have now reached a length, which allows the wave to free

    i tse lf from the cable. The apparatus rad iates an

    electromagnetic wave, whereby the length of the two bent

    pieces of wire corresponds to half of the wavelength. This

    is the basic principle of /2-dipole antenna.

    The Principle of an antenna continued:-

    An electrical field

    (E) is created due to the

    voltage potential (V) butalso a magnetic field (H)

    which is based on the

    current (I) The amplitude

    distribution of both fields

    corresponds to the voltage

    and current distribution on

    the dipole.

    S-16

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    Field distribution on a Dipole

    The free propagation of the wave from the dipole is achieved by the permanent

    transformation from electrical into magnetic energy and vice versa. Thereby the resulting

    electrical and magnetic fields are at right angles to the direction of propagation

    Half-Power-Beam-Width

    This term defines

    the aperture of the

    antenna. The HPBW is

    defined by the points in

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    the horizontal and vertical diagram, which show where the radiated power has reached half

    the amplitude of the main radiation direction. These points are also called 3 dB points.

    Normally only the major lobe is considered for this.

    S-17

    Gain

    An antenna without gain radiates energy in every direction. An antenna with gain

    concentrates the energy in a defined angle segment of 3-dimensional space. The l/2-dipole

    is used as a reference for defining gain. At higher frequencies the gain is often defined with

    reference to the isotropic radiator. The isotropic radiator is a non-existent ideal antenna,

    which has also an omni directional radiation characteristic in the E-plane and H-plane.

    Impedance

    The impedance of the antenna is simply equal to the voltage applied to its input

    terminals divided by the current flow. The frequency dependent impedance of a dipole or

    antenna is often adjusted via a symmetry or transformation circuit to meet the 50-Ohm

    criterion. Adjustment across a wider frequency range is achieved using compensation

    circuits.

    VSWR of 1.5 is standard within mobile communications. In this case the real

    component of the complex impedance may vary between the following values:

    Maximum Value: 50 Ohms x 1.5 = 75 Ohms

    Minimum Value: 50 Ohms / 1.5 = 33 Ohms

    The term return loss attenuation is being used more often in recent times. The reason

    for this is that the voltage ratio of the return to the forward-wave Vr/Vi can bemeasured via a directional coupler. This factor is defined as the co-efficient of

    reflection. Figure shows the relationship between the coefficients of reflection; return

    loss attenuation, VSWR and reflected power.

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    S-18

    Omni directional Antennas:

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    The classical omni directional lamda/2 antennas are of two types

    1. Ground Plane

    2. /4-skirt Antenna

    S-19

    The names indicate how the antenna is decoupled from the mast.In both cases the

    horizontal radiation pattern covers 360 and vertical half power beamwidth is 78 .Hence

    there will be lot of waste of energy both upwards and downwards in the desired horizontal

    plane.

    Ground Plane Omni Directional Antenna

    In this case, a conductive plane is

    achieved via 3 counterweighted poles. The

    ground p lane antenna can cover the

    complete frequency range because it is a

    wideband antenna.

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    S-20

    lamda/4-skirt Antenna

    In this case , the

    decoupling is achieved by using a

    /4-skirt but this antenna works

    for limited range of frequency.

    Directional Antennas

    Directional antennas are provided with reflectors behind the radiating element. This

    focuses the energy in a desired direction avoiding transmission in the rear side of the

    antenna. The directional antennas are classified into the following types:

    1.Grid Parabolic Reflector antennas

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    2. Parabolic Reflector antennas.

    3.Cassegrain antennas.

    4. Array antennas

    The first two types of antennas are mainly used in fixed point-to-point radio links and thegrid types are employed up to 2GHz whereas the solid parabolic reflector antennas are used

    for higher frequencies. The connectivity between the antennas to the equipments is by coaxialcable up to 2GHz and for higher frequencies it is by hollow copper tube called wave-guide.

    S-21

    The beam width of these antennas depends on the diameter of the antenna and frequency of

    operation. They produce very narrow beams

    Directional Antennas

    Cassegrain antennas are associated with Satellite communication are comparatively

    larger which makes them to be fixed on the ground or roof tops and orient themselves

    towards the satellite by operating gear arrangement either manually or using motors.

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    S-22

    (UNIT-4)

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    S-23

    TECHNIQUES

    Duplexing and Multiple access Technique:-

    In Telecom network conventionally each user is connected to the Telephone

    exchange individually.This dedicated pair starts from MDF,where it is connected to the

    appropriate Equipment point and ends at the customer premises Telephone.(with flexibility

    at cabinet/pillar/ distribution points DPs)

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    S-24

    Duple Xing is the technique by which the send and receive paths are separated over

    the medium.

    There are two types of duplexing.

    Frequency Division Duplexing FDD

    Time Division Duplexing TDD

    Frequency Division Duplexing (FDD)

    Different Frequencies are used for send and receive paths and hence there will be a forward band and

    reverse band

    Duplexer is needed if simultaneous transmission(send) and reception methodology is adopted

    Frequency separation between forward band and reverse band is constant

    Time Division Duplexing (TDD)

    TDD uses different time slots for transmission and reception paths

    Single radio frequency can be used in both the directions instead of two as in FDD.

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    No duplexer is required, Only a fast switching synthesizer,RF filter path and fast antenna switch are

    needed.It increases the battery life of mobile phones

    S-25

    Multiple Access Techniques

    The technique of dynamically sharing the finite limited radio spectrum by multiple

    users is called Multiple Access Technique. By adopting multiple access techniques all users

    can not get the services simultaneously and some amount of blocking is introduced by the

    system. This is known as GOS( Grade of Service).

    Generally there are 3 types. They are

    Frequency Division Multiple Access (FDMA)

    Time Division Multiple Access (TDMA)

    Code Division Multiple Access (CDMA)

    Frequency Division Multiple Access

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    FDMA is a famil iar method of

    allocating bandwidth,where a base station

    is allowed to transmit on one or more

    number of preassigned carrier frequencies

    and a mobile unit transmits on

    corresponding reverse channels. No other

    base station within range of the mobile will

    be transmitt ing on the same forward

    channel, and no other mobile within range

    of the base station should be transmitting

    on the same reverse channel. Both the

    base and the mobile usual ly transmit

    continuously during a conversation, and fully occupy their assigned forward and reverse

    channels. No other conversation can take place on these channels until the first

    conversation is completed.

    S-26

    Features Of Frequency Division Multiple Access(FDMA)

    No Precise coordination in time domain is necessary in FDMA System.

    It is well suited for narrow band analog systems.

    Guard spacing between channels causes wastage of frequency resource.Otherwise good modulation

    techniques are to be employed to avoid such guard spacing.

    The transmission is simultaneous and continuous and hence duplexers are needed .Continuous

    transmission leads to shortening of battery life.

    FDMA Analogy

    It may be easier to visualize FDMA by imagining a cocktail party where two people

    wish to converse with each other.Then everyone in the room must be silent except for the

    speaker. The speaker may talk as long as they wish, and when they finish someone else

    may start speaking, but again only one at a time. New speakers must wait (or find another

    party) for the current speaker to finish before starting. Everyone in the room can hear and

    understand the speaker, unless they are too far away or the speaker's voice is too soft.

    If the intended listener is close enough, the speaker may decide to whisper.

    Conversely, if the listener is too far away, the speaker may have to shout. Since no one

    else should be talking, this presents no problem. If someone talks out of turn, the listener

    will probably be confused and not be able to understand either speaker.

    Time Division Multiple Access (TDMA)

    TDMA is a more efficient, but more

    complicated way of using FDMA channels.

    In a TDMA system each channel is split up

    into time segments, and a transmitter is

    g iven exc lus ive use of one or more

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    channels only during a particular time period. A conversation, then, takes place during the

    time slots to which each transmitter (base and mobile) is assigned. TDMA requires a master

    time reference to synchronize all transmitters and receivers.

    TDMA was the first digital standard to be proposed, and a smooth transition took

    place between analog mobile systems to digital mobiles, by allowing simultaneous existence

    of analog and digital base stations.

    Features of TDMA

    There can be only one carrier in the medium at any time, if a simple TDMA scheme is followed.

    Transmission is in bursts and hence is well suited for digital communication.

    Since the transmission is in bursts, Battery life is extended.

    Transmission rate is very high compared to analog FDMA systems .

    Precise synchronization is necessary.

    Guard time between slots is also necessary

    TDMA Analogy

    In TDMA, everyone in the room agrees to watch a clock on the wall, and speak only

    during a particular time. Each person wishing to talk is given a set period of time, and each

    person listening must know what that time period will be. For example, everyone may agree

    on time slots with a duration of ten seconds. Speaker number one may talk for ten seconds

    starting from the top of the minute.

    The listener who wishes to hear this speaker must also be made aware of the

    schedule, and be ready to listen at the top of the minute. Speaker number two may speak

    only from ten seconds after the minute until twenty seconds after. As with FDMA, only one

    person at a time may speak, but each speaker's time is now limited and many persons may

    take their turn. If someone in the room cannot see the clock, they will not be able to speakand will have great difficulty understanding the speakers.

    CDMA is fundamentally different than TDMA and FDMA. Where FDMA and TDMA

    transmit a strong signal in a narrow frequency band, CDMA transmits a relatively weak

    signal across a wide frequency band. Using a technique called direct sequence spread

    spectrum, the data to be transmitted are combined with a pseudo-noise code (a pre-

    determined binary sequence that appears random) and transmitted broadband.CDMA under

    Interim Standard 95 uses a bandwidth of 1.25 MHz.

    The pseudo-noise code (PN code) is a series of binary "chips" that are much shorter

    in duration than the data bits. Since the chips appear to be in a random pattern, and there

    are many chips per data bit (in IS-95 there are 128 chips for each data bit), the modulatedresult appears to normal (FDMA) receivers as background noise.

    A spread spectrum receiver with a different PN code will not be able to recover that

    signal, and if the PN codes were chosen incorrectly, will hear nothing but noise. This

    relative immunity to interference, whether from outside sources or other spread spectrum

    transmitters, gives CDMA systems the ability to pack many users into the same frequency

    space at the same time. It also gives a measure of security to each signal, since each user

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    will have a different PN code. CDMA also does not require different base station radios for

    each user - the same radio may serve multiple users with just a change in PN code

    Code Division Multiple Access (CDMA)

    CDMA is fundamentally different than TDMA and FDMA. Where FDMA and TDMA

    transmit a strong signal in a narrow frequency band, CDMA transmits a relatively weak

    signal across a wide frequency band. Using a technique called direct sequence spread

    spectrum, the data to be transmitted are combined with a pseudo-noise code (a pre-

    determined binary sequence that appears random) and transmitted broadband.CDMA under

    Interim Standard 95 uses a bandwidth of 1.25 MHz.

    The pseudo-noise code (PN code) is a series of binary "chips" that are much shorter

    in duration than the data bits. Since the chips appear to be in a random pattern, and there

    S-27

    are many chips per data bit (in IS-95 there are 128 chips for each data bit), the

    modulated result appears to normal (FDMA) receivers as background noise.

    A spread spectrum receiver with a different PN code will not be able to recover that

    signal, and if the PN codes were chosen incorrectly, will hear nothing but noise. This

    relative immunity to interference, whether from outside sources or other spread spectrum

    transmitters, gives CDMA systems the ability to pack many users into the same frequency

    space at the same time. It also gives a measure of security to each signal, since each user

    will have a different PN code. CDMA also does not require different base station radios for

    each user - the same radio may serve multiple users with just a change in PN code.

    CDMA Analogy

    In CDMA, the speaker and the listener have agreed beforehand to use a language

    that no one else at the party understands. Many speakers may talk at a CDMA party, each

    using a different language, and it is relatively easy for the listener to hear and understand

    the speaker as long as there aren't too many speakers talking at the same time. As more

    and more speakers start talking, the noise level in the room goes up and it becomes harder

    and harder for the listener to make out what their speaker is saying. If a speaker begins to

    shout, in order for their listener to hear better, it raises the noise level even more

    Capacity of FDMA system:-

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    N number of channels

    Bt total spectrum

    Bguard guard band

    B c channel bandwidth

    S-28

    Capacity of a TDMA system:-

    N number of channels , m number of TDMA users per radio channel

    B tot..total spectrum allocation Bguard Guard Band B cchannel Bw

    Capacity of CDMA System

    There is a limit to CDMA capacity, however, and it is essentially the amount of

    interference a CDMA receiver can tolerate. As more and more units transmit, the amount of

    noise a receiver sees goes up, since all signals not using the receiver's specific PN code

    appear as noise. At some point there is so much noise that the receiver can no longer hear

    the transmitter. Boosting the transmitter power won't help overall, since it increases the

    noise for all the other receivers, who would in turn tell their transmitters to boost power,

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    and the situation remains.In a nutshell, if a unit near a base station is transmitting with too

    much power, signals from units far from the base station will be lost in the noise

    S-29

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    CELLULAR CONCEPTS

    What is a cell?

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    Cell is the basic geographic unit.They are base stations transmitting over that small

    area.Cells are usually represented on paper as hexagon.In reality the shape is not so

    because of the landscape and man-made structures.The base stations can be employing

    omni directional or directional antenna.

    Cell size depends on sub density and demand in that given area. To start with cell

    can be of maximum size 30Km radius and subsequently can be split into smaller cells.

    Usually in rural areas the cells are big and in urban will be smaller.

    What is a cluster?

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    Cluster is a group of cells. No channel is reused within the cluster.Cells using the

    same frequencies will be in adjacent clusters. Hence the cluster size determines the reuse

    distance.

    Cluster Size

    Cluster size is usually denoted by N or K(no.of cells in that cluster).A cluster must bemore or less symmetrical and similar North/South and East/West dimensions. We cannot

    select cluster size arbitrarily. Cluster sizes must satisfy the fo llowing:

    N (K)= i2+ij+j2 where i and j are nonnegative integers. Thus N = 1, 3, 4, 7, 9, 11, 12..

    Cellular Concepts

    Different types of cells

    Macro cells

    Micro cells

    Selective cells

    Umbrella cells

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    Macrocells

    The macrocells are large cells for remote and sparsely populated areas.

    Microcells

    These cells are used for densely populated areas. By splitting the existing areas

    into smaller cells, the number of channels available is increased as well as the capacity of

    the cells. The power level of the transmitters used in these cells is then decreased,

    reducing the possibility of interference between neighboring cells.

    Selective Cells

    It is not always useful to define a cell with a full coverage of 360 degrees. In some

    cases, cells with a particular shape and coverage are needed. These cells are called

    selective cells. A typical example of selective cells is the cells that may be located at theentrances of tunnels where a coverage of 360 degrees is not needed. In this case, a

    selective cell with a coverage of 120 degrees is used.

    Umbrella cells

    A freeway crossing very small cells produces an important number of handovers

    among the different small neighboring cells. In order to solve this problem, the concept of

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    umbrella cells is introduced. An umbrella cell covers several microcells. The power level

    inside an umbrella cell is increased comparing to the power levels used in the microcells

    that form the umbrella cell. When the speed of the mobile is too high, the mobile is handed

    off to the umbrella cell. The mobile will then stay longer in the same cell (in this case the

    umbrella cell). This will reduce the number of handovers and the work of the network.

    Cellular Concepts - Cluster size and interference

    The cells in the adjacent clusters using the same set of frequencies are called co-

    channel cells. The interference depends on the reuse distance between them.

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    GSM ARCHITECTURE

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    The figure represents a GSM reference model for a PLMN (Public Land Mobile

    Network).

    The GSM network is divided into four major systems

    Switching system (SS)

    Base station system (BSS)

    Mobile station (MS)

    Operation and maintenance centre(OMC)

    The switching system (SS) also called as Network and Switching System(NSS) is

    responsible for performing call processing and Subscriber-related functions. The switching

    system includes the following functional units

    Mobile Switching Centre

    Home Location Register

    Visitor Location Register

    Equipment Identity Register

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    GSM Architecture - Mobile Switching Centre

    MSC (Mobile Switching Centre) MSC performs all switching functions for all mobile

    stations, located in the geographic area controlled by its assigned BSSs.Also it interfaces

    with PSTN, with other MSCs, and other system entities.

    GSM Architecture - The Functions Of MSC

    Call handling that copes with the mobile nature of subscribers considering Location Registration,.

    Authentication of subscribers and equipment, Handover and Prepaid service.

    Management of required logical radio link channel during calls

    Management of MSC-BSS signaling protocol

    Handling location registration and ensuring interworking between mobile station and VLR.

    Controls inter BSS and inter MSC hand overs.

    Acting as a gateway MSC to interrogate HLR. The MSC which is connected to the PSTN/ISDN network is

    called as GMSC.This is the only MSC in the network connected to the HLR.

    Standard functions of a switch like charging

    GSM Architecture - Home Location Register (HLR)

    Home location register contains

    The identity of mobile subscriber called IMSI (International Mobile Sub Identity)

    ISDN directory number of mobile station.

    Subscription information on services.

    Service restrictions.

    Location Information for call routing

    One HLR per GSM network is recommended and it may be a distributed database.

    Permanent data in HLR changed by man-machine interface. Temporary data like location

    information changes dynamically

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    GSM Architecture - Visitor Location Register (VLR)

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

    new MSC area, the VLR connected to that MSC would 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.

    VLR contains information like

    Identity of mobile sub

    Any temporary mobile sub identity

    ISDN directory number of the mobile

    A directory number to route the call to the roaming station.

    Part of the data of HLR for the mobiles that are currently located in MSC service area.

    GSM Architecture - Equipment Identity Register

    Equipment Identity Register consists of identity of mobile station equipment called

    IMEI (International Mobile Equipment Identity), which may be valid, suspect and prohibited.

    When a mobile station accesses the system the equipment validation procedure is evoked

    before giving the services.

    The information is available in the form of three lists.

    White list-The terminal is allowed to connect to the Network.

    Grey List-The terminal is under observation from the network for the possible problems.

    Black List-The terminals reported as stolen are not type approved They are not allowed to connect to the

    network

    EIR informs the VLR that in which list the particular IMEI is.

    GSM Architecture - Authentication Centre

    It is Associated with a HLR. It stores an Identity key called Authentication key (Ki)

    for each Mobile subscriber. This key is used to generate The authentication triplets

    RAND (Random Number)

    SRES (Signed Response) -To authenticate IMSI

    Kc (Cipher Key) - To cipher communication over the radio path between the MS and the network.

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    GSM Architecture - Operation and Maintenance Centre (OMC)

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    It is the functional entity through which the network operator can monitor and

    control the system by performing following functions

    Software installation

    Traffic Management

    Performance data analysis

    Tracing of subscribers and equipment.

    Configuration management

    Subscriber administration.

    Management of mobile equipment.

    Management of charging and billing.

    GSM Architecture - Base Station System(BSS)

    BSS connects the MS and the NSS.

    It is composed of

    1.Base Transceiver Station (BTS) also called Base Station.

    2.Base Station Controller (BSC).

    BTS and BSC communicate across the standardized Abis interface. BTS is controlled

    by BSC and one BSC can have many BTS under its control

    GSM Architecture - Base Transceiver Station (BTS)

    BTS houses the radio transceivers and handles the radio-link protocols with the Mobile

    Station.Each BTS comprises of radio transmission and reception devices including antenna,

    signal processors etc. Each BTS can support 1 to 16 RF carriers

    The parameters differentiating the BTSs are Power level, antenna height, antenna type and

    number of carriers.

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    Functions of BTS:-

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    It is responsible for Time and Frequency synchronization

    The process of channel coding, Encryption, Multiplexing and modulation for Trans direction and reverse

    for reception are to be carried out.

    It has to arrange for transmission in advance from the mobiles depending upon their distance from BTS.

    (Timing Advance)

    It has to detect Random access requests from mobiles, measure and monitor the radio channels forpower control and handover

    Base Station Controller:

    BSC manages the radio resources for one or a group of BTSs

    It Handles radio-channel setup, frequency hopping, handovers, and control of the RF power

    levels.BSC provides the time and frequency synchronization reference signals broadcast by

    its BTSs.It establishes connection between the mobile station and the MSC.BSC is

    connected via interfaces to MSC,BTS and OMC

    GSM Architecture - Mobile Station

    It refers to the terminal equipment used by the w ireless subscriber. It consists of

    SIM -Subscriber Identity Module

    Mobile Equipment.

    SIM is removable and with appropriate SIM, the network can be accessed

    using various mobile equipments.

    The equipment identity is not linked to the subscriber.

    The equipment is validated separately with IMEI and EIR.

    The SIM contains an integrated circuit chip with a microprocessor, random

    access memory (RAM)and read only memory (ROM).

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    SIM should be valid and authenticate the validity of MS while accessing the

    network.

    SIM also stores subscriber related information like IMSI ,cell location

    identity etc.

    Functions of Mobile Station:-

    Radio transmission and reception.

    Radio channel management.

    Speech encoding/decoding.

    Radio link error protection.

    Flow control of data.

    Rate adaptation of user data to the radio link.

    Mobility management.

    Performance measurements upto a maximum of six surrounding BTSs and reporting

    to the BSS, MS can store and display short received alphanumeric messages on the liquid

    crystal display (LCD) that is used to show call dialing and status information.

    There are five different categories of mobile telephone units specified by the

    European GSM system: 20W, 8W, 5W, 2W, and 0.8W.

    These correspond to 43-dBm, 39-dBm, 37-dBm, 33-dBm, and 29-dBm power levels.

    The 20-W and 8-W units (peak power) are either for vehicle-mounted or portable

    station use.

    The MS power is adjustable in 2-dB steps from its nominal value down to 20mW (13

    dBm). This is done automatically under remote control from the BTS

    GSM Architecture - Transcoders

    Transcoders are a network entity inserted to interface the MSC side to Mobile

    side .The voice coding rate on the PSTN side is 64Kbps and in GSM over the air the Voice is

    coded as 13Kbps.To reduce the data rate over the air Interface and to reduce the loading of

    the terrestrial link (4 : 1),transcoders are introduced at an appropriate place, mostly with

    MSC.

    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 Kbps by inserting additional

    synchronizing data to make up the difference between a 13-Kbps speech or lower rate data

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    GSM Interfaces

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    Introduction

    The GSM network is shown in the figure with the major interfaces indicated as Um,

    Abis and A

    The air interface is used for exchanges between a MS and a BSS.

    Abis

    This is a BSS internal interface linking the BSC and a BTS, and it has not been

    standardised. The Abis interface allows control of the radio equipment and radio frequency

    allocation in the BTS.(2M link)

    A

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    A interface is between the BSS and the MSC. The A interface manages the

    allocation of suitable radio resources to the MSs and mobility management. (2M link CCS7)

    B

    The B interface is between the MSC and VLR. Most MSCs are associated with a VLR,

    making the B interface "internal". Whenever the MSC needs access to data regarding a MS

    located in its area, it interrogates the VLR.

    C

    The C interface is between the HLR and a GMSC or a SMS-G. Each call originating

    outside of GSM (i.e., a MS terminating call from the PSTN) has to go through a Gateway to

    obtain the routing information required to complete the call. (2M link CCS7)

    D

    The D interface is between the VLR and HLR, to exchange the data related to the

    location of the MS and to the management of the subscriber. (2M link CCS7)

    GSM Interfaces

    E

    The E interface interconnects two MSCs. The E interface exchanges data related to

    handover between the anchor and relay MSCs.(2M link CCS7)

    F

    The F interface connects the MSC to the EIR, to verify the status of the IMEI that

    the MSC has retrieved from the MS.(2M link CCS7)

    G

    The G interface interconnects two VLRs of different MSCs to transfer subscriber

    information, during e.g. a location update procedure. (2M link CCS7)

    GSM Interfaces-H Interface

    The H interface is between the MSC and the SMS-G, to support the transfer of short

    messages. (2M link CCS7)

    Um Interface

    It is the air interface between mobile and BTS. There are uplink and downlink

    frequency bands. The carriers are spaced at 200KHz. Each carrier is providing 8 timeslots.

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    GSM Interfaces-Physical Channel and Logical Channel

    Physical Channel

    The carrier number and the repetitive time slot number determine Physical Channel

    (e.g.) time slot 3 on carrier number 4. The duration of timeslot in GSM is 577 micro secs

    (15/26 ms). The transmission is digital and is in bursts and hence in GSM, physical channel,timeslot and burst refer to the same.

    Logical Channel

    The content or message of physical channel is logical channel. One or more logical

    channels can be mapped to one physical channel. For example, on one of the physical

    channel used for traffic,traffic is sent by using TCH (traffic channel) message while a

    handover message is transmitted using FACCH (Fast Associated Control Channel message).

    Traffic channels TCH

    Broadcast channels BCH

    Common Control Channels CCCH.

    Dedicated Control Channels DCCH

    Traffic Channels

    Traffic channels are used to send data or services. Once the call set up procedures

    are completed on the control channels, MS tunes to a traffic physical channel.It uses the

    Traffic Channel logical channel. Traffic channel carries speech or data traffic.

    Speech is encoded into 13Kbps digital stream by using a special algorithm called

    Regular Pulse Excited- Linear Predictive Coder with Long Predictor Loop. Basically

    information from previous samples which does not change very quickly is used to predict

    the current sample. The coefficients of linear combinations of previous samples, plus an

    encoded form of the residual, the difference between the predicted and actual sample

    represent the signal.

    Traffic channels are classified into two types

    Full Rate TCH/F:It transmits full rate speech (13Kbps). A full rate TCH occupies one physical channel

    Half Rate TCH/H :It transmits half rate speech(6.5 Kbps). Two half rate TCHs can share one physical

    channel to double the capacity

    There are enhanced full rate coders, (12.2Kbps) which improve the speech quality

    but still occupy one full rate TCH. Data rates supported by speech coders: A full rate trafficchannel can support data rate of 9.6Kbps and a half rate channel 4.8 Kbps.

    Broadcast Channels BCH

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    Helps the MSs to orient themselves in the mobile radio network. They are Point to

    multi point channels ( BTS to MSs). They are defined for the down link direction only.

    Types of Broad Cast Channels

    Broad Cast Control Channels-BCCH

    Frequency Correction Channel-FCCH

    Synchronization Channel-SCH

    Cell Broadcast Channel-CBCH

    Broadcast Control Channel (BCCH)

    Through the BCCH logical channel MS is informed about the system configuration

    parameters like

    Local Area Identity

    Cell Identity

    Identity of BCCH carrier frequencies of Neighbor cells.

    Max trans power of MS to access

    Configuration of control channels

    BCCH is also known as beacon. Each cell/sector will have one carrier frequency on

    which BCCH will be broadcasted.

    Frequency Correction Channel-FCCH

    The logical Channel contains no information (continuous zeros) but pure carrier is

    transmitted so that the mobile can tune itself and synchronise with the frequency. FCCH

    will be transmitted in the same beacon carrier as BCCH.

    Synchronisation Channel-SCH

    This logical channel transmits information about TDMA frame structure in a cell

    /sector (frame number) and Base Station Identity Code which can be decoded only if the

    BTS belongs to the network for which the MS has subscribed. SCH will also be transmitted

    in the same carrier of FCCH and BCCH.

    Cell Broadcast Channel- CBCH

    This logical channel contains messages that can be received by all mobiles. These

    messages are sent by using dedicated channels and come under the category of short

    messages. However, they are considered as common channels since all mobiles can receive

    them.

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    They operate either in up link or down link directions and are point-to-point simplex

    channels

    Types of Common Control Channels

    PCH-Paging Channel

    AGCH-Access GrantChannel

    RACH- Random Access Channel

    Paging Channel-PCH

    It is logical channel in the downlink direction and it is point-to-point type. It

    comprises of a paging message to indicate an incoming call or short message. The paging

    message consists of the identity of mobile the network wants to contact.

    Access Grant CHannel-AGCH

    It is a point-to-point logical channel in the downlink direction. It informs the mobile

    about the assignment of signaling channel for call set-up i.e. SDCCH.

    Random Access CHannel (RACH)

    It is a point-to-point logical channel in the uplink direction. It is sent by the mobile

    as a request for making a call or as a response to a paging to the mobile. It consists of the

    identity of the mobile and location area details as available in SIM.

    GSM Frame Structure and Burst Types:

    GSM, one time slot duration is 0.577ms(15/26ms). One TDMA frame carries 8

    timeslots and hence duration of one frame is 4.612ms.

    Separate multiframes are defined for traffic and control signals.

    A 26-frame TDMA multi frame is def ined for carrying TCH, SACCH and

    FACCH.Duration of this multiframe is 4.612x26=120ms(15/26x8x26).

    A 51-frame TDMA multiframe is defined for control multiframe for carrying BCCH,

    CCCH, SDCCH and its associated SACCH. The durat ion of such multi frame is4.612x51=235ms.

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    A superframe is defined which consists of 51 traffic multiframes or 26 control

    mutiframes and duration of superframe is 6.312s.It represents smallest cycle for which the

    organization of all channels is repeated.

    A hyperframe is defined which consists of 2048 superframes. The duration of such

    frame is 3Hrs 28mts 53 secs and 760 msecs (2715648 frames). This represents the

    smallest cycle for frequency hopping and ciphering

    GSM Frame Structure

    Traffic Multiframe

    Traffic Multiframe is defined with 26 frames. The length of a 26-Multiframe is 120

    ms. Of the 26 frames, 24 are used for traffic, 1 is used for the Slow Associated Control

    Channel (SACCH), and 1 is unused in case of full rate channel deployment.In case half rate

    channels are used the frame 25 is used for SACCH for the second set of calls.

    If FACCH is to be sent then pre-emption of traffic channel is employed. Hence the

    logical channel combinations that are allowed can be either

    TCH/F+SACCH/F+FACCH/F or

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    TCH/H+SACCH/H+FACCH/H.

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    GSM Bursts

    Burst is the content of the timeslot. The duration of timeslot is 577 micro secs. It

    consists of usable bits and guard period. The burst are classified into.

    Normal Burst

    Dummy Burst

    Frequency Control Burst(F-Burst)

    Sync Burst(S-Burst)

    Access Burst

    F-Burst is associated with FCCH, S-burst with SCH and Access Burst with RACH. All

    other logical channels use normal burst. Dummy Burst is used to fill the empty physical

    Normal Bursts

    It consists of 148 usable bits and guard period corresponding to 8.25 bits.(30.5

    micro secs).

    Burst period= time slot duration- guard period= 577-30.5 =546.5 micro secs.

    It consists of three tail bits each at the beginning and end, encrypted data bits 57each as two blocks and a midamble of 26 bits as training sequence, a known pattern used

    for adoptive equalization at BTS and MS. The flag bits are used to indicate whether the

    particular block of 57 bits belong to TCH or FACCH during pre-emption

    Dummy Bursts

    It is transmitted in Idle time slots on the BCCH Carrier,which ensures that the

    BCCH Carrier is always present and MS is able to find it easily and carry out the assessment

    of signal level.This helps in Mobile Assisted Hand Over(MAHO)

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    Frequency Correction Burst F-burst

    It is associated with FCCH and transmitted in TS0 in frames 0,10,20,30,and 40 th

    frames in a control multiframe. This burst also consists of three tail bits each at the

    beginning and end, guard period of 8.25 bits w ith a string of 142 zeros

    (3+142+3+8.25=156.25). Since the information is only zeros, after modulation pure carrier

    is transmitted.

    Sync Bursts(S-Burst)

    It is associated with SCH and is transmitted in TS0 of frames 1,11,21,31 and 41 th

    frames in a control multiframe. This burst consists of three tail bits each at the start and

    end, guard period of 8.25 bits with two blocks of 39 bits of information and a training

    sequence of 64 bits sand witched in between them. This is the first burst in the downlink

    direction to be processed by the MS.The longer training sequence helps the MS to

    effectively demodulate the signal from BTS

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    Different Modes of Operation

    The different logical channels are used to take MS from Off modeto Idle mode

    and then to Dedicated mode.

    Off Mode

    MS is in the Switched Off condition.It cannot receive incoming paging messages or

    cannot make outgoing call and No dedicated channel is associated with it.

    Idle Mode

    MS Switched On and it is attached to the network and can receive incoming paging

    messages, can make outgoing call, but there is no dedicated channel associated with it

    Dedicated Mode

    MS is in conversation and a dedicated channel is associated with it.

    Abis Interface

    It is connectivity between BSC to BTS and 2 Mbps link is established for this

    purpose. Every timeslot of 64Kbps can be sub divided into four 16 Kbps and the traffic of

    13Kbps from BTS with the associated signaling information is multiplexed as 16Kbps and

    inserted in the timeslots. Hence each timeslot on 2Mbps Abis can accommodate four

    physical channels of Um. For one carrier we need two slots. Additionally we require

    exclusive timeslots for signaling purposes related to the transceivers of each sector (TRX)

    and for O andM purposes.

    Consider a BTS with three sectors with 4 Carriers in each sector (4/4/4), then the

    timeslot calculations are as follows:

    In each sector each TRX needs 2 slots. Hence four TRXs need 8 slots. We need one

    slot for TRXs signaling purposes and one for O and M purposes in that sector.

    Therefore total slots needed per sector= 8+1+1=10

    Three sectors need 30 slots and TS0 is reserved for FAW and the total comes 31.

    With one spare timeslot added it tallies to 32 slots of 2Mbps link. Hence one 2Mbps link to

    BTS can take a maximum load until the BTS reaches a configuration 4/4/4

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    GSM Radio Link

    Introduction

    BTS and MS are connected through radio link this air interface is called Um.A radio

    wave is subject to attenuation,reflection,Doppler shift and interference from other

    transmitter.These effects causes loss of signal strength and distortion which will impact the

    quality of voice or data. To cope with the harsh conditions,GSM make use of an efficient

    and protective signal processing. Proper cellular design must ensure that sufficient radio

    coverage is provided in the area.

    Types of signal strength variations

    The signal strength variation for mobile is due to different types of signal strength

    fadings.

    There are two types of signal strength variations

    Macroscopic Variations

    Due to the terrain contour between BTS and MS the fading effect is caused

    by shadowing and diffraction(bending) of radio waves.

    Microscopic variations

    Due to multipath, Short-term or Rayleigh fading. As the MS moves, radio

    waves from many different paths will be received.

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    Macroscopic Variations

    Macroscopic Variations can be modeled as the addition of two components that

    make up the path loss between mobile and base station.the first component is the

    deterministic component(L) that adds loss to the signal strength as the distance(R)increases between base and mobile.this component can be written as

    where n is typically 4.

    The other macroscopic component is a Log normal random variable which takes into

    account the effects of shadow fading caused by variations in terrain and other obstructions

    in the radio path. Local mean value of path loss=deterministic component+log normal

    random variable

    Microscopic Variations

    Microscopic Variations or Rayleigh Fading occur as the mobile moves over short

    distances compared to the distance between mobile and base. These short term variations

    are caused by signal scattering in the vicinity of the mobile unit e.g. by hill,building or

    traffic. The result is that not one but many different paths are followed between transmitter

    and receiver(Multipath Propagation) The reflected wave will be altered in both phase and

    amplitude.The signal may effectively disappear if the reflected wave is 180 degree out of

    phase with the direct path signal. The partial out of phase relationships among multiple

    received signal produce smaller reduction in received signal strength.

    Effects caused by Rayleigh fading

    Reflection and multipath propagation can cause positive and negative effects.

    Coverage Extension

    Multipath propagation allow radio signal to reach behind hills , buildings and into

    tunnels.

    Constructive and destructive interference

    Signals received through multi paths may add together or destroy each other

    Transmitting/Receiving Processes

    There are two major processes involved in transmitting and receiving information

    over a digital radio link;coding and modulation.

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    Coding

    Coding is the information processing that involves preparing the basic data signals

    so that they are protected and put in a form that the radio link can handle.Generally the

    coding process includes the Logical Gate exclusive OR(EXOR).

    Coding is included in :

    Speech coding or Trans coding

    Channel coding or Forward Error Correction coding

    Interleaving

    Encryption

    Multiplexing(Burst formatting)

    Speech Properties

    Human speech can be distinguished in elementary sounds(Phonemes).Depending on

    the language there are 30 to 50 different phonemes.The human voice is able to produce up

    to 10 phonemes per second,so that about 60 bit/s are required to transfer the

    speech.However,all individual features and intonations would disappear.To preserve the

    individual features,the real amount of information to be sent is a number of times

    higher,but still a fraction of the 64 Kbit/s used for PCM.

    Based upon the phoneme production mechanism of the human organs of speech,a

    simple speech production model can be made. It appears that during a short time interval

    of 10-30 ms,the model parameters like pitch-period, voiced/unvoiced,amplification gain,and

    filter parameters remain about stationary(quasi stationary). The advantage of such a model

    is the simple determination of the parameters by means of linear prediction.

    Speech coding techniques

    Human speech is band limited between 300Hz to 3400Hz and undergoes Frequency

    Modulation in analog systems.In digital fixed PSTN systems band limited speech is sampled

    at the rate of 8KHz and each sampled is encoded into 8 bits leading to 64Kbps(PCM A-Law

    of encoding).Digital cellular radio cannot handle the high bit rate used for PSTN

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    systems.Smart techniques for signal analysis and processing have been developed

    for reduction of the bit rate.

    There are 3 classes of speech coding Techniques

    Waveform coding : Speech is transmitted as good as possible in wave form coding.PCM is an example

    of waveform coding. Bit rate ranges from 24 to 64kbps and the quality of speech is good and the speaker

    can be recognise easily.

    Parameter Coding : Only a very limited quantity of information is sent.A decoder built up according to

    the speech production model will regenerate the speech at the receiver.Only 1 to 3kbps is required for

    the speech transmission. The regenerated speech is intelligible but it suffers from noise and often the

    speaker cannot be recognised.

    Hybrid Coding: Hybrid Coding is a mix of waveform coding and parameter coding.It combines the strong

    points of both technique and GSM uses hybrid coding technique called RPE-LTP(Regular Pulse Excited-

    Long Term Prediction) resulting in 13Kbps per voice channel.

    Speech Coding in GSM(Transcoding)

    The 64kbits/s PCM transcoded from the standard A-law quantized 8bits per sample

    into a linearly quantised 13bits per sample bit stream ,that correspond to a 104kbits/s bit

    rate. The 104kbits/s stream is fed into the RPE-LTP speech encoder which takes the 13 bits

    samples in a block of 160 samples (every 20ms). RPE-LTP encoder produces 260bits in

    every 20 ms, resulting in a bit rate of 13kbits/s.This provides a speech quality acceptable

    for mobile telephony and comparable with wireline PSTN phones.In GSM 13Kbps speech

    coding is called full rate and alternatively half rate coders(6.5Kbps) are also available to

    enhance the capacity.

    Channel Coding /Convolutional Coding

    Channel coding in GSM uses the 260 bits from speech coding as input to channel

    coding and outputs 456 encoded bits.Out of the 260 bits produced by RPE-LTP speech

    coder, 182 are classified as important bits and 78 as unimportant bits. Again 182 bits are

    divided into 50 most important bits and are block coded into 53 bits and are added with

    132 bits and 4 tail bits,totaling to 189 bits before undergoing 1:2 convolutional

    coding,converting 189 bits into 378 bits.These 378 bits are added with 78 unimportant bits

    resulting in 456 bits.

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    Channel Coding

    Interleaving - First Level

    The channel coder provides 456 bits for every 20ms of speech.These are

    interleaved,forming eight blocks of 57 bits each,as shown in figure below.

    In a normal burst to blocks of 57 bits can be accommodated and if 1 such burst is

    lost there is a 25% BER for the entire 20ms.

    Interleaving - Second Level

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    A Second level of interleaving has been introduced to further reduce the possible

    BER to 12.5% . Instead of sending two blocks of 57 bits from the same 20 ms of speech

    within one burst,a block from one 20ms and a block from next sample of 20ms are sent

    together.A delay is introduced in the system when the MS must wait for the next 20ms of

    speech.However,the system can now afford to loose a whole burst,out of eight,as the loss is

    only 12.5% of the total bits from each 20ms speech frame.12.5% is the maximum loss level

    that channel decoder can correct.

    Encryption /Ciphering

    The purpose of Ciphering is to encode the burst so that it may not be interpreted by

    any other devices than the receiver. The Ciphering algorithm in GSM is called the A5

    algorithm.It does not add bits to the burst,meaning that the input and output to the

    Ciphering process is the same as the input:456 bits per 20ms.Details about Encryption is

    available under the special features of GSM.

    Multiplexing(Burst Formatting)

    Every transmission from mobile/BTS must include some extra information along

    with basic data. In GSM a total of 136 bits per block of 20ms are added bringing the overall

    total to 592 bits. A guard period of 33 bits is also added bringing 625 bits per 20ms.

    Modulation

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    (UNIT-9)

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    Mobile To Land Call Scenario (Mobile Origination)

    Phases of Mobile To Land Call . The following table lists the phases of a Mobile To

    Land Call

    Request for services;the MS requests to setup a call

    Authentication : the MSC/VLR requests the AUC for authentication parameters,Using these parameters

    the MS is authenticated.

    Ciphering : using the parameters, which were made available earlier during the authentication, the uplink

    and the downlink are ciphered

    Equipment Validation :the MSC/VLR requests the EIR to check the IMEI for validity

    Call setup :the MSC establishes a connection to the MS.

    Handover(s)

    Call release;the speech path is released

    Mobile To Land Call Scenario-Phases of Mobile To Land Call

    The user enters the digits of the telephone with STD code incase of land line or

    without STD code incase of mobile and presses the "send" key after all digits have been

    entered

    MS transmits a channel request message over the Random Access Channel(RACH)

    Once the BSS receives the Channel Request message,it allocates a Stand-alone Dedicated Control

    Channel(SDCCH) and forwards this channel assignment information to the MS over the access Grant

    Channel(AGCH).It is over the SDCCH that the MS will communicate with the BSS and MSC until a traffic

    channel is assigned.

    The MS transmits a service request message to the BSS over the SDCCH.Included in this message is

    the MS TMSI and Location Area Identification(LAI).The BSS forwards the service request message to the

    MSC/VLR.

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    Mobile To Land Call Scenario-Phases of Mobile To Land Call

    Equipment Validation

    The Mobile Equipment(ME) validation process is the means by which a specific piece

    of ME can be identified to prevent the use of stolen, unauthorized or malfunctioning

    equipment in the network.

    Each equipment is uniquely identified by an International Mobile Equipment Identity

    (IMEI) code. IMEI which is incorporated into ME by the manufacturer,has three

    components,such as

    Type approval code (TAC)

    Final Assembly Code (FAC)

    Serial Number (SNR)

    The IMEI code is secure and physically protected against unauthorized change.

    The Equipment Identity Register(EIR) is responsible for storing the IMEI codes that

    identify the mobile-equipment deployed in the GSM system.

    Steps in Equipment Validation

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    At this point in time,the MS has been authenticated and the radio channel is being

    encrypted.The MSC will interrogate the MS for its equipment number and checks the

    equipment against information in the Equipment Identity Register(EIR)

    The MSC transmits a request to the MS requesting it to respond with its IMEI

    The MS upon receiving this request,reads its equipment serial number and returns this value to the MSC

    The MSC then requests the EIR to check the IMEI for validity.The EIR will first check to see if the IMEI

    value is within a valid range.If so,it then checks to see if the IMEI is on a suspect or known list of invalid

    equipment

    The EIR returns to the MSC the results of the IMEI validation.If the results are negative,the MSC might

    abort the call or possibly let the call continue but inform the network service provider of the event.In this

    scenario we will assume that the IMEI is

    Land-to-Mobile Call scenario

    The following table lists the phases of a land -to-mobile call

    Routing Analysis :the MS terminated call is routed to the visited MSC using information from HLR and

    VLR

    Paging :the MSC initiates a communication with the MS

    Authentication :the MSC/VLR requests the ACC for authentication parameters.Using these parameters

    the MS is authenticated

    Ciphering :using the parameters which were made available earlier during the authentication the uplink

    and the downlink are Ciphered

    Equipment Validation : the MSC/VLR requests the EIR to check the IMEI for validity.

    Call setup :the MSC establishes a connection to the MS

    Handover(s)

    Call release :the speech path is released.

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    Land-to-Mobile Call scenario

    Optional Phases

    The authentication ciphering,equipment validation and handover phases are

    optional;the service provider may decide that some of these phases might not take place in

    a land-to-mobile call

    The following is a scenario of a mobile-terminating call.It is assumed that the MS is

    already registered with the system and has been allocated a Temporary Mobile Identity

    Number(TMSI). It is also assumed that a land subscriber dials the directory number of the

    mobile subscriber and the call enters the GSM network via a Gateway MSC(GMSC)

    The PSTN routes the call to the GMSC of this directory number.based on the Mobile Subscriber ISDN

    Number(MSISDN)

    The GMSC not knowing whether this MS is roaming in its own service area or not s ends a message with

    the MSISDN in it to the HLR

    The HLR requests the MSC/VLR to provide routing information about this

    The MSC/VLR returns to the GMSC via the HLR a directory number where the MS can be reached which

    is referred to as the MS Roaming Number(MSRN)

    The call is routed from the GMSC to the visited MSC

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    Steps in Paging Phase

    The MSC uses the location area identity,provided by the VLR to determine when BSSs should page the

    MS.The MSC transmits a message to each of these BSSs requesting that a page be performed.Included

    in the message is the TMSI of the MS.

    Each of the BSSs broadcasts the TMSI of the mobile in a page message on the paging channel

    When a MS detects its TMSI of the Mobile in a page message on the paging channel(PCH)

    Once the BSS receives the Channel request message,it allocates a Stand-alone Dedicated Control

    Channel(SDCCH) and forwards this channel assignment information to the Ms over the Access Grant

    Channel(AGCH).It is over the SDCCH that the MS will communicate with the BSS and MSC until a traffic

    channel is assigned.

    The MS transmits a page response message to the BSS over the SDCCH.Included in this message is

    the MS TMSI and Location Area Identification

    The BSS forwards the page response message to the MSC.The MSC informs its VLR that a particular

    MS is responding to a pag

    Phases of Mobile To Land Call

    Authentication,Ciphering and Equipment Validation Phases

    The Authentication and Ciphering phases that might be performed here to setup a

    mobile-to-land call are the same as seen before in the location update scenarios.The

    Equipment Validation phase is done in the same way as in the mobile- to-land scenario

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    The call with the mobile is setup;a voice path is created between the MS and the MSC

    by allocating a radio traffic channel and a voice trunk

    After the MSC receives a setup a voice path is created between the MS is informed that a call will be

    setup via a setup message

    The MS upon receiving upon receiving a setup message,performs comp ability checking before

    responding to the setup message.It is possible that the MS might be incompatible for certain types call

    setps.Assuming that the passes comp ability checking it acknowledges the call setup with a setup

    confirm message

    Authentication,Ciphering and Equipment Validation Phases

    In this scenario it is assumed that the mobile subscriber answers the phone.The MS in response to this

    action stops alerting and sends a connect message to the MSC

    The MSC removes audible to the PSTN and connects the PSTN trunk to the BSS trunk(terrestrial

    channel) and sends a connect message via the GMSC to the PSTN.The caller and called party now have

    a complete talk path.This event typically denotes the beginning of the call for billing purposes

    The MSC sends the MS a connect acknowledgment

    Steps in release phase network initiated

    The release triggered by the land user is done in a similar way as the release

    triggered by the mobile user

    The MSC receives a Release message from the network to terminate the end-to-end connection

    This cause the sending of a disconnect message toward the MS

    The MS answers by a release message.The MSC release the connection to the PSTN.

    Phases of mobile-to-mobile call scenario

    The mobile-to-mobile call is established using the same phases as seen earlier

    The originating mobile part where the phases are the same as those of a mobile-to-land call except that

    the call setup phase is partially performed.Which means that only the call setup with Mobile is done

    The terminating mobile part consist of the same phases as the land-to-mobile call scenario except again

    that the call setup phase performs only the call setup with mobile

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    (UNIT-10)

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    Mobility Management

    Network Attachment

    Network attachment is a process of selecting an appropriate cell(radio frequency)by

    the mobile station to provide the available services,and making its location known to the

    network

    The process starts when the mobile station is switched on,and ends when the

    mobile station enters the idle mode.In idle mode the mobile station does not have a traffic

    channel allocated to make or receive a call,but the Public Land Mobile Network(PLMN) is

    aware of the existence of the mobile station within the chosen cell.

    Network Attachment Process

    Cell Identification

    When a mobile station is switched on it attempts to make contact with a GSM PLMN

    by performing the following action

    Measures the BCCH channels.

    Search for a suitable cell.

    The mobile station measures the signal strength of the BCCH(Broadcast Control

    Channel)channels received.It stores in a list of information of about 30 of these BCCH

    channels,such as the signal strength and the frequency corresponding to these BCCHchannels.

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    PLMN selection

    A suitable PLMN is chosen.

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    Cell Selection

    It is a process of selecting an appropriate cell(radio frequency)by the mobile station

    to provide the available services

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    6.FINAL RESULT :-

    (a) BSNL is Indias first which provided free incoming facility for theircustomer.

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    (b) BSNL introduces following services as per order

    1. Prepaid Mobile with National roaming.

    2. Post Paid Mobile with International roaming.

    3. Also providing many value added services likes GPRS,Roaming,Clip,Friend &family ,SMS,MMS Etc.

    (B ) In keeping in view the competition from other players,BSNL isrevising its tariff for benefit of users.

    7. CONCLUSION :-

    .Keeping up with technological and market changes, BSNL has been

    able to maintain its lead in provisioning Mobile services using GSMtechnology

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    8. SCOPE OF FUTURE STUDY:-

    3G Squeeze: GSM, LTE & the Future of Wideband CDMA

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    The much-longer-than-anticipated cycle of operator investment in 2G GSMand Enhanced Data rates for GSM Evolution (EDGE) networks combined

    with moves by Verizon Wireless, NTT DoCoMo, and others to bring forwardthe commercial timescale for 4G UMTS Terrestrial Radio Access Network(UTRAN) Long Term Evolution a plain old 2G GSM phone today, rather than a3G W-CDMA phone.

    Over the last 18 months, HSPA has finally started to deliver on the mobile

    broadband marketing promise of 3G that has been bandied about since thelate 1990s. There is genuine excitement on the part of users at being able to

    get out their lapt(LTE) is creating something of a "3G squeeze" onWideband CDMA (W-CDMA) and its High Speed Packet Access (HSPA)releases. Continued high global investment in

    GSM/EDGE, combined with industry-wide disappointment in the performance

    of W-CDMA up until very recently, have served to containinvestment in W-CDMA for either voice or data services. As a

    result, more than three out of four Europeans still uses opsacross extensive urban and suburban areas and consistently get

    at least 1 Mbit/s throughput over the air. Yet just as W-CDMA isfinally starting to differentiate itself from 2G and establish itself

    as the preferred global platform for mobile broadband services, itfaces the prospect of being made redundant by an acceleration in

    the time to market of the 4G mobile WiMax and LTE standards.These technologies have been designed to be deployed in muchlarger spectrum channel widths and offer better spectralefficiency, higher throughput, and lower latency than anything W-

    CDMA/HSPA can support.3G Squeeze: GSM, LTE & the Future of Wideband CDMA

    delivers a complete analysis of the technology progressionscenarios in mobile networks worldwide. Drawing on inputs from

    major GSM and W-CDMA/HSPA operators such as America Movil,AT&T, China Mobile, Millicom International, Orascom Telecom,and Vodafone, as well as interviews with major vendors, the

    report weighs the underlying technology, business, consumer,and regulatory dynamics that will determine the propensity ofoperators in different regions of the world to shift capex away

    from one technology and into another. The report assesses whichmarket factors will have a material impact on the direction of

    operator capex and which won't, and forecasts global operator

    capex on GSM/EDGE, W-CDMA/HSPA, and LTE technologythrough 2012.

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    9. REFERENCES:

    1. BSNL MANUALS

    2. www.bsnl.co.in

    3.www.punjab.bsnl.co.in

    4. BSNL BTS at BRS Nagar, Ludhiana

    5. BSNL BSC at Bharat Nagar Chowk, Ludhiana

    6.BSNL MSC at Sec-34, Chandigarh.

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    CERTIFICATE

    This is certified that Mr. BANARASEE LAL has completed hisproject work on Mobile Communication using GSM Technology;

    BSNL under my direct supervision and guidance.

    This project work done by him is original one and has not beensubmitted to any other institution for fulfillment of the requirement of

    a course of study.

    He completed his project work in 6 weeks from 13 Dec 08 to 24 Jan

    09.

    I wish him best of luck and success in future.

    Dr J. S. Sohal , FIE