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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
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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.
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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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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.
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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
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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
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(Unit-3)
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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.
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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.
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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.
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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.
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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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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
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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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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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(UNIT-4)
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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
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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.
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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
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(UNIT-5)
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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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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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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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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