Training Gsm Basic

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GSM Foundation Course

• Course Content

Basic Telephony & Cellular

Principal of Cellular Communication

GSM Features

GSM Network Components

GSM Terrestrial Interfaces

Basic GSM Processes

GSM Air Interface

Radio Interface Optimization, Supplementary services &

Contemporary Networks

3

ESSAR Telecom

• Telecom Service Provisions

– GSM

– Basic

– Internet

• ESSAR

– GSM Service Provider in Punjab, Delhi,

Rajasthan, U.P (East) & Haryana – Basic Service Provider in the state of Punjab.

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Service Industry

• Service Provider is not a Equipment

Manufacturer.

• The Service Provider has a license to operate in a

geographical boundary (state/circle/ country).

• It buys equipment from OEM Suppliers (Vendors).

• Installs & commissions the equipment thus

making it’s own Network.

• Provides the desired service to it’s subscribers.

ESSAR CELLPHONE

Punjab

Haryana

U.P (East)Rajasthan

Delhi

Coverage Area

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ORGANISATION STRUCTURE

PROMOTERS

TECHNICAL

PLANNING

IMPLEMENTATION

OPERATIONS

OPERATIONS SYSTEM SUPPORT

BILLING

IT

ACTIVATIONS

MARKETING

CUSTOMER CARESALES

SUPPORT FUNCTIONS

HR, ADMIN, ACCOUNTS



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Basic Telephony

•Off Hook

•Dial Tone

•Dialing Digits

•RBT

•Conversation

•Ring

•Off Hook &Conversation

•Signaling•Traffic

SWITCH / EXCHANGE

8

2 Mb E1 (PCM)

Sample Rate 8 kHz8 bits per sample

64 kbps

1

31

16

0

300 - 3400 Hz

1st TCH

17th TS

30thTCH

15th TCH

9

Wireless Telephony

BSC

BTS BTS

Mobile Subscriber...

MSC

10

Wireless Communication

• Alternative means of wireless communication

– Walkie - Talkie

– Pagers

– Trunked private radios

• Mobile Phone - the magic technology that enableseveryone to communicate anywhere with anybody.

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12

Cellular Communication

• A cellular system links Mobile subscribers to Public

Telephone System or to another Mobile subscribers.

• It removes the fixed wiring used in a traditional

telephone installation.

• Mobile subscriber is able to move around, perhaps

can travel in a vehicle or on foot & still make & receive

call.



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Advantage of Cellular Communication

• Mobility

• Flexibility

• Convergence

• Greater QOS

• Network Expansion

• Revenue/Profit

WHAT IS CELLULAR TELEPHONY ?

CONSIDERATIONS -

FREQUENCY

SUBSCRIBERDENSITY

COVERAGE

Base Station

Base Station

Base Station

Base StationBase Station

Base Station

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The Cell

• Cellular Radio involves dividing a large service area

into regions called “cells.”

• Each cell has the equipment to switch, transmit and

receive calls.

• Cells - Reduce the need of High powered transmission

• Cells - Conventionally regarded as being hexagonal,

but in reality they are irregularly shaped.

• Cell shape is determined by the nature of the

surrounding area e.g. Hills , tall building etc.

The CELL

What is a cell ?

A cell is a certain areathat can be reachedwith one transceiver

or

A small collection of

transceivers ondifferent channels at asingle base site.

The hexagonal-shaped communication cells areartificial & are generated to simplify the planning &design of a cellular network.

BTS

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Coverage & Capacity

• Coverage

– Percentage of the geographical area coveredby cellular service where mobile telephony isavailable

• Capacity -

– Number of calls that can be handled in acertain area within a certain period of time.

– Capacity can also refer to the probability thatusers will be denied access to a system due tothe simple unavailability of radio channels.

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Cells



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Cell Size

• Large Cells

• 35 Km

• Remote Areas

• High Transmission

Power

• Few subscribers

• Small Cells

• Near about 1 KM

• Urban Areas

• Low Transmission

Power

• Many Subscribers

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MICRO CELL

Below Rooftop~ Railway Platforms, Airports,~ Busy Shopping Bazaar etc.

Low Tx Power~ 1 Watt max.

Limited Coverage~ 200m - 500m

Hotspot Solution

Special Algorithms for HO

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PICO CELLS

Pico Cell

Inside offices, Buildings

Very Low Tx Power~ Less than 1 Watt

Limited Coverage~ 50 -100m

Capacity Solution

Special Algorithms for HO

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Analog Mobile Telephony

• End of 1980’s Analog Systems unable to

meet continuing demands

– Severely confined spectrum allocations

– Interference in multipath fading environment

– Incompatibility among various analog systems

– Inability to substantially reduce the cost of

mobile terminals and infrastructure required

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Digital Mobile Telephony

• Spectrum space - most limited and precious

resource

• Solution - further multiplex traffic (time

domain)

• Can be realized with Digital Techniques only.

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Different Standards Worldwide

• Till 1982 Cellular Systems were exclusively

Analog Radio Technology.

• Advanced Mobile Phone Service (AMPS)

– U.S. standard on the 800 MHz Band

• Total Access Communication System (TACS)

– U.K. standard on 900 MHz band

• Nordic Mobile Telephone System (NMT)

– Scandinavian standard on the 450 & 900 MHz

band



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GSM History and Organization

• 1979 Europe wide frequency band reserved forCellular

• 1982 “Groupe Speciale Mobile” created withinCEPT

• 1986 GSM had full time in Paris

• 1988 ETSI takes over GSM Committee

• 1990 The phase 1 GSM Recommendationsfrozen

• 1991 GSM Committee renamed “Special MobileGroup” and GSM renamed as “ GlobalSystem for Mobile Communication”

• 1992 GSM is launched for commercialoperations

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GSM - IN CELLULAR TELEPHONY

• Each Cell in the Cellular Network consists of oneor more RF carriers.

• An RF carrier is a pair of radio frequencies

– One used in upward direction by MS - Uplink

– Other used in downward direction by BTS -Downlink

– The transmit and receive frequencies areseparated by a gap of 45 MHz in GSM of 75MHz in DCS.

• There are 124 carries in GSM Band. With eachcarrier carrying 7 timeslots, only 124 x 7 = 868calls can be made!

• Frequency Reuse is the solution

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Uplink-Downlink

Downlink = 935 to 960 MHz

Uplink = 890 to 915 MHz

BTS Tx MS Rx

BTS Rx MS Tx

dl

ul

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Frequency & ARFCN

Ful(n) = 890.0 + (0.2) *n MHz

Fdl(n) = Ful + 45 MHz

where n =ARFCN ; 1 ≤≤≤≤ n ≤≤≤≤ 124

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0 7

3

0

5

01

2

0 7

3

0

5

01

2

TDMA & FDMA

F D M A

200KHz

Uplink - MS Tx890MHz to 915MHz

Downlink - BTS Tx935MHz to 960MHz

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GSM Burst & TDMA Frame

0 1 2 3 4 5 6 7 2 4 5 6 730 1

FRAME 1 FRAME 2

Training sequenceInformation Information

GUARD PERIOD GUARD PERIOD

TAIL BITS TAIL BITS



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Frequency Reuse Pattern

Three types of frequency reuse patterns

• 7 Cell reuse pattern

• 4 cell reuse pattern

• 3 cell reuse pattern

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Cell Dia = R

FREQUENCY RE - USE

– Frequency Re-use

7/21 cell cluster

1

2

3

4

5

6

7

Two re-use distances

D D/R = (3N)1/2

where N is Cluster size

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Principal Of Sectorization

• Omni Directional Cells

• 120 degree Sectors

• 60 Degree sectors

– Each Sector in a Site has its own allocation ofRadio Carriers.

• Advantage – By frequent reuse of frequency more

capacity can be achieved.

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a1

a2

a3a3

a4a6

a5

Cell Sectorisation

OMNI CELL

1 ANTENNA

b1

b2

b3

120O CELLS

3 ANTENNAS

60O CELLS

6 ANTENNAS

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3 Site Reuse Pattern

c2

c1

c3

a1

a2

a3

b1

b2

b3

c1c2

c3

Cell Re-use

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Cellular 1Planning Steps

– Cellular Topology

• Cell splitting & Cell Repeat Patterns

3 cluster site 3/9 cell cluster 4 cluster site 4/12 cell cluster

Sites in the middle



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GSM Antennas

• Directional Antennas

• Vertically Polarized.

• Collinear Dipole Array with

8 to 12 elements.

• Beam Width 45o, 60o, 90o.

• High Gain Antennas with

gain of 16 to 18 dbi.

• Mechanically/Electrically

Downtiltable.

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Features of GSM

• Compatibility

• Noise Robust

• Increased Capacity & Flexibility

• Use of Standard Open Interfaces

• Improved Security & Confidentiality

• Cleaner Handovers

• Subscriber Identification

• ISDN Compatibility

• Enhanced Range of Services

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Compatibility

• With rapid Developments

there was a need for a

common Standard for

Mobile Communication.

• With GSM, one could

drive from Germany to

Spain without a Call

Drop.• Due to versatility of GSM,

it was adopted by many

countries, even outside

Europe.

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Noise Robust

• To combat the problems

due to Noise-

Digital Interface is used.

• Digital Interface

– Protect these errors

using Error Detection &

Correction Techniques.

– Immune to higher levels

of noise and interference

– Improvements in Quality

as well as Efficiency-

Robust Air Interface.

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Increased Capacity and Flexibility

• Analogue Air Interface

– Every connection requires a

separate RF carrier and thus

RF hardware.

– System Expansion

• Time Consuming

• Costly & Labor Intensive.

• Intricate RF Planning.

• Digital Interface

– 8 simultaneous conversations

on one RF carrier.



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Standardized Open Interfaces

• Low Price

– Uses standard interfaces like C7, X.25 etc.

Versatility to choose equipment from different

manufacturer thereby reducing the pricing

monopoly.

• Flexibility

– Great flexibility in situating Network

components because of Standard Interfaces.

– Efficient use of terrestrial links.

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Better Security & Confidentiality

• High Security risk for

Analogue System operators.• GSM

– No Eavesdropping

– High speech and data

confidentiality.

– Digitized, Encoded and

Encrypted (A8 algorithm)

– Subscriber Authentication

(A3 algorithm)

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Cleaner Handovers

• The mobile measures up to 32 adjacent cells for

– Signal Strength (RxLevel)

– Signal Quality (RxQual)

– updated every 480 mS and sends to BTS

• Sophisticated Handover based on

– RxLevel

– Interference

– RxQual

– Timing Advance

– Power Budget

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Base Station 2

Base Station 3

Base Station 1

Handovers

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ISDN Compatibility

• ISDN (Integrated Services Digital Network)

– Advanced Telecom Network designed to carry

voice and user data over the standard

telephones lines.

• 2B+D Signalling and information on ISDN line.

• The GSM Network is designed to operate within

the ISDN System.

• GSM provides features compatible with ISDN.

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GSM NETWORK ELEMENTS

PSTNEC

MSC

HLR

AUC

VLR

EIRIWF

TRAU BSC

BTS

Network Switching System

BSS

SIM

ME

MS

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GSM Network Components

• Mobile Station consists of two parts-

– Mobile Equipment (ME)

– Subscriber Identity Module (SIM)

• ME

– Hardware e.g. Telephone, Fax Machine,

Computer.

• SIM

– Smart Card which plugs into the ME. NETCOMP

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Mobile Equipment (ME)

• ME are of three types-

– Vehicle Mounted

– Portable Mobile Unit

– Handportable Unit

• ME’s have distinct features-Classmarks sent in

initial message to Network.

NETCOMP

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ME (Classmark Information)

• Revision Level

– Phase of the GSM specs ME comply with.

• RF Power Capability

– Max power ME is able to Transmit.

• Ciphering Algorithm Used

– Presently A5

– Phase 2 specifies Algorithms A5/0 to A5/7.

• Frequency Capability

• SMS CapabilityNETCOMP

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TypicalSettings

Mobile Equipment

Class Power O/p

1 20 W

2 8 W

3 5 W

4 2 W

5 0.8 W

NETCOMP



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SIM

Subscriber Interface Identity

Module

The SIM stores

– Subscriber Parameters

– Personal Data for identifying

Subscriber to the Network.

– IMSI,, MSISDN, PIN, PUK, Ki,

A3, A8 (for Kc generation)

– Space reserved for TMSI &

LAI

--------------

--------------

Small SIM

Full Size SIM Card

--------------

--------------

NETCOMP

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SIM - Internal Structure

CPU

EEPROM

RAM

ROM

I/O

8

User Data 16 kB

Basic Operating System

16 to 24 kB

Working Area for CPU256 to 512 bytes

NETCOMP

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SIM(IMSI)

• IMSI(International Mobile Subscriber Identity)

– Transmitted over Air Interface on initialization

– Permanently stored on SIM card

– 15 digit Decimal

MCC (3) MNC (2) MSIC (10)

NETCOMP

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• LAI (Location Area Identity)

– MCC 3 digit number (BCD), two Octets ( A & B)

– MNC 2 digit number (BCD), one Octet

– LAC 3 digit number (Binary) , two Octets

0-65535 – CI 5 digit number (Binary) , two Octets

0-65535

SIM (LAI)

LACMCC MNC CI

NETCOMP

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SIM

• MSISDN

– 10 digit number to which a subscriber is beingcalled.

• PIN (Personal Identification Number)

– Four digit PIN

– An internal security to Protect the SIM fromillegal use.

– Card blocks itself after three wrong entries

• PUK (Personal Unblocking Key)

– 8 digit code to unblock the SIM Card

• Ki (Authentication Key), A3 & A8 AlgorithmsNETCOMP

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SIM (TMSI)

• Temporary Mobile Subscriber Identity

– Periodically changed by the SystemManagement on instances like location updateetc.

• Reason for use of TMSI

– To prevent a possible intruder from identifyingGSM users, TMSI is used

• Management

– Assignment, Administration & Updating isperformed by VLR.

NETCOMP



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Transcoder

• Converts 64 Kbps PCM circuits from MSC to 16

Kbps BSS circuits.

• Each 30 channel 2 Mbps PCM link can carry 120

GSM - specified voice channels.

NETCOMP

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Transcoder

MSCBSS

XCDR120 GSM TCH

1 2 3 4

Transcoder Information from FOUR calls

(4x16 KBPS put into ONE 64 KBPS timeslot

30 Channel PCM

1234

NETCOMP

63 64

Base Station System (BSS)

• BSS (Base Station System)

– BSC (Base Site Controller)

– BTS (Base Transceiver Station)

– XCDR (Transcoder)

NetworkSwitchingSystem(NSS)

XCDR

BSC

BTSNETCOMP

BTS

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Base Station System (BSS)

• BSC

– Controls upto 40 BTS

– Conveys information to/from BTS

– Connects terrestrial circuits & Air InterfaceChannels

– Controls handovers between BTSs under itself

• BTS

– Contains RF Hardware

– Limited control functionality

– 1 - 6 carriers in a BTS Cabinet

– 7 - 48 simultaneous calls per BTSNETCOMP

BTS

66

A BTS Cabinet

OUTER VIEWINNER VIEWNETCOMP



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BSS Configuration

• Collocated BTS

• Remote BTS

• Daisy Chain BTS

• Star Configuration

• Loop Configuration

NETCOMP

BTS

68

Daisy Chain Configuration

BSC

BTS

BTS

BTS NETCOMP

A l l B T S on1 E 1

69

Star Configuration

BSC

BTS

BTS BTS

BTS

NETCOMP

70

Loop Configuration

BSC

BTS

BTS BTS

BTS

Loop Configuration

NETCOMP

71

Network Switching System(NSS)

• NSS (Network Switching System)

– MSC (Mobile Switching Centre)

– HLR (Home Location Register)

– VLR (Visitor Location Register)

– EIR (Equipment Identity Register)

– AUC (Authentication Centre)

– IWF (Interworking Function)

– EC (Echo Canceller)NETCOMP

MSC

72

MOBILE SWITCHING CENTRE

NETCOMP



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GSM Network Component

• MSC

– Call Switching

– Operation & Management Support

– Internetwork Interworking

– Collects call billing data

• Gateway MSC

– MSC which provides interface between PSTN &BSS’s in the GSM Network.

NETCOMP

74

Home Location Register (HLR)

• Reference database for the Subscriber profiles-

– Subscriber ID (IMSI & MSISDN)

– Current VLR Address

– Supplementary Services subscribed

– Supplementary Service Information

– Subscriber Status (Registered/deregistered)

– Authentication Key and AUC functionality

– TMSI

– MSRNNETCOMP

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Visitor Location Register (VLR)

• Temporary Data, which exists as long as thesubscriber is active in a particular Coverage area.

• Contains the following-

– Mobile Status (Busy/ Free/ No Answer/etc.)

– Location Area Identity (LAI)

– TMSI

– MSRN (Mobile Station Roaming Number)

NETCOMP

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Equipment Identity Register (EIR)

• Contains Database for validating IMEI

– White List (valid ME)

– Black List (Stolen ME)

– Grey List (Faulty ME)

NETCOMP

77

• Provides function to enable the GSMSystem to interface with Public/PrivateData Networks.

• The basic feature of the IWF are

– Rate Conversion

– Protocol adaptation

• IWF incorporates Modem Bank.

e.g. GSM DTE PSTN DTE

IWF Analogue Modem

Inter Working Function

NETCOMP

78

Echo Canceller

• Echo is apparent only in Mobile - Land

conversation & is generated at the 2 wire to 4 wire

interface.

• To avoid it, Echo Canceller (EC) is used.

– Echo is irritating to MS Subscriber

– Total Round Trip delay of 180 ms in the GSM

system

– EC is placed on the PSTN side of the Switch

– Cancellation up to 68 ms with ECNETCOMP



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Operation & Maintenance Centre

• Event & Alarm Management

• Fault Management

• Performance Management

• Configuration Management

• Security Management

o The OMC has access to the (G)MSC, BSC.

o Handles error messages being reported from theNetwork

o Controls the traffic load of the BSC, and the BTS.

Operation & Maintenance Centre

o NETWORK MANAGEMENT CENTRE(NMC)

– Offers Hierarchical Regionalised Network

Management of a complete GSM system.

• Functionality of the NMC

• Monitors Nodes on the Network

• Monitors Network Element Statistics

• Monitors OMC regions & provides

information to OMC staff

• Enables Long Term Planning for

entire Network

NETWORK MANAGEMENT CENTRE

MMI RAM>

MMI RAM>MMI RAM>

NMC

OMC OMC

OMC

REGION 2

REGION 3

REGION 1

NETWORK

NETWORK MANAGEMENT CENTRE

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GSM Terrestrial Interfaces

Broadly classified into two types of interfaces-

• Standard Interfaces

– 2 Mbps Trunks (E1)

– Signalling System No. 7 SS7 ( CCS7)

– X.25 (Packet Switched Mode)

• GSM Interfaces

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GSM Interfaces

• Um MS - BTS

• Abis BTS - BSC

• A BSC - MSC

• B MSC - VLR

• C MSC - HLR

• D VLR - HLR

• E MSC - MSC

• F MSC - EIR

• G VLR - VLR

• H HLR - AUC



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85

86

87

Basic Processes

• AUTHENTICATION

• CIPHERING

• REGISTRATION

• CALL ESTABLISHMENT

• HANDOVER / HANDOFF

• ROAMING

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AUTHENTICATION ALGORITHM

NSS

MS

HLR

AUC

AUTH.ALGORITHMS

A3

SIM

MS

AUTH.ALGORITHMS

A3

Ki

RAND

RAND

COMPARE

SRES

SRES

Ki

AIR INTERFACE

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Ciphering

• Data protection is required on air interface.

• A5 algorithm is used.

• A specific key called Ciphering Key (Kc), isgenerated from RAND and A8 algorithm.

• A8 is on the SIM.

A8

RANDKi

Kc90

Ciphering

A5Data

Kc

Ciphered

DataA5

Kc

Data



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ROAMING

MSC

ME

ME

PSTN

MSC

VLR

HLR

INDIA

UK

o The mobile roams to another country (UK) and requests a

Location Update when switched ‘ON’.

o The VLR (UK) informs the home HLR (India) of the mobile’s

new location (UK).

o The HLR updates its location information and sends the

subscriber information to the VLR (UK).

o The HLR requests the subscriber information be removed

from the VLR (India).

o The VLR (India) acknowledges, and removes the subscriber

information from its database.

o After the mobile’s registrat ion is completed in UK’s

MSC/VLR, the mobile is able to use network services (MOC,

MTC etc.)

ROAMING

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Transmission Media

• Access Network

– Microwave 15 /23 GHz

• Backbone Network

– Microwave 7 GHz

– Optical Fibers

– Leased Line( From Dot or any other

service provider on any media)

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Access Microwave ( 15 GHz)

• 14.250 to 14.500 MHz and

14.400 to 15.350 MHz

• 4 QAM & 16 QAM Modulation

• Split Mount Version with Hot

Standby Facility

• Bandwidth ranging from 1.25

MHz to 28 MHz dependingupon Data Rate and

Modulation type

• 4 E1 Radio with 3 spot

frequencies in our case

95

Backbone Microwave (7 GHz)

• 7.125 to 7.850 MHz and 7.725

to 8.500 MHz

• 4 QAM & 16 QAM Modulation

• Split Mount Version with hot

standby facility

• Bandwidth ranging from 1.25

MHz to 28 MHz depending

upon Data Rate and

Modulation type

• 16 E1 Radio with 1 spot

frequencies in our case

96

Optical Fiber

• Low Losses 0.5 dB/km & High Data Rates

• Types of Fiber

– Step Index

– Graded Index

# Graded Index are better.

Modes of Light in fiber

– Mono Mode

– Multi Mode

# Mono Mode has less losses than Multi

Mode.



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Optical Fiber

• Different Possible Combinations

• Mono Mode Step Index 10 / 125 µµµµm

• Mono Mode Graded index

• Multi Mode Step Index 100 / 300 µµµµm

• Multi Mode Graded Index 75 / 130 µµµµm

• Mono Mode Graded Index would have been

the best but fabrication not possible

140 Mbps OLTE , Mono Mode Step Index in our case

98

99

Channels On Air Interface

• Physical Channel

• Logical Channel

• Physical Channel

– Physical channel is the medium over which theinformation is carried.

• Logical Channel

– Logical channels consists of the informationcarried over the Physical Channel.

100

0 7

3

0

5

01

2

0 7

3

0

5

01

2

TDMA & FDMA

F D M A

200KHz

Uplink - MS Tx890MHz to 915MHz

Downlink - BTS Tx935MHz to 960MHz

101

LOGICAL CHANNELS

0 1 2 3 4 5 6 7

3

57encrypted

57encrypted

26training

1

S

1

S

3

T

8.25

GP

3T

577µµµµS

577µµµµS x 8 = 4.615mS

TDMA Frame

Normal Burst

26 Frame Multi-frame

102

BURST

• Time is divided into discrete periods

called “Timeslots”

• The Time Slots are arranged in a sequence

, conventionally numbered 0 to 7.

• Each repetition of this sequence is called

a TDMA Frame.

• The information content carried in one

time slot is called a “burst”.





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109

BCCH Channel

CCH

BCCH

BCCHSynchronizing Channels

FCHSCH

Broadcast ControlChannel - Downlink only

110


• BCCH

– Transmitted at all times & conveys informationabout Cell Timing and Configuration

• BCCH, FCCH, SCH

• CCCH

– Used by BSS & MS when trying to initiate aconnection over the air

• RACH, PCH, AGCH, CBCH

111


• DCCH

– Used to convey signaling information duringcall setup

• SDCCH

• ACCH

– Used to transmit signaling information when acall is in progress

• FACCH & SACCH

112


• ACCH

– SAACH

• Conveys Power Control & Timing

Information in the downlink direction.

• RSSI and Quality reports in the uplink

direction.

– FACCH

• To carry out user authentication andhandovers. It steals the TCH burst andinserts its own information.

113


• Acronyms

– BCCH Broadcast Control Channel

– CCCH Common Control Channel

– DCCH Dedicated Control Channel

– ACCH Associated Control Channel

– SDCCH Standalone Dedicated Control Channel

– RACH Random Access Channel

– PCH Paging Channel

– AGCH Access Grant Channel

114


• BCCH – Location Area Identity

– List of neighbouring cells, to be monitored

– List of frequencies used in the cell

– Cell Identity

– Power Control Indicator

– DTX permitted

– Access Control (e.g emergency calls, call

barring)



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115


– Always transmitted at constant power at all

times – Dummy burst are sent to ensure continuity

when no traffic information is sent.

• FCCH

– Mobile corrects the frequency of its internal

time base by reading this logical channel.

– Easily detected by the mobile.

– After FCCH, mobile is able to detect SCH

which contains timing information.

116


• SCH

– Carries the information for mobile to

synchronize to the TDMA frame structure &

know the timing of the individual timeslots.

– Frame Number & BSIC (Base Station Identity

Code)

• CCCH

– RACH

• Transmitted by the Mobile when it wishes to

gain access to the system

117


– PCH

• Transmitted by the BTS when it wishes to

contact a specific mobile.

– AGCH

• Transmitted by the BTS to assign dedicated

resources to an MS such as SDCCH

– CBCH• To transmit messages to all mobiles within

a cell. CBCH will steal some time of an

SDCCH to do this.

118

Channel Combinations

• Full rate Traffic Channel Combination

– TCH8/FACCH + SACCH

• Broadcast Channel Combination

– BCCH + CCCH

• Dedicated Channel Combination

– SDCCH8 + SACCH8

• Combined Channel Combination

– BCCH + CCCH + SDCCH4 + SACCH4

119

Channel Combinations (Timeslots)

– Traffic Channel Combination

• TCH8/FACCH +SACCH

• Can be on any Time slot

– Broadcast Channel Combination

• BCCH +CCCH

• Can be on Timeslot 0, 2, 4, 6

– Dedicated Channel Combination

• SDCCH8 + SACCH8

• Any Time slot

– Combined Channel Combination

• BCCH + CCCH +SDCCH4 + SACCH4

• Can only be on 0 Timeslot

120

TCH Multiframe

0 5 10

SACCH

15 20

IDLE

Downlink & Uplink SACCH





22

127

Channel Coding

• Error Protection And Detection

– To protect the logical channel fromtransmission errors by the radio path, differentcoding schemes are used.

• Coding & Interleaving Schemes dependent uponlogical channel to be encoded.

• 3 Coding Protection schemes

– Speech Channel Encoding

– Control Channel Encoding

– Data Channel Encoding

128

Speech Channel Coding

• Speech Information of 20 ms block is divided

over 8 GSM burst.

• 260 bits are grouped in three classes depending

upon the intelligible part of speech

• After encoding 456 bits block is interleaved

129

Speech Channel Coding

Parity

Check

456 bits

Class 1b

132 bits

Class 1a

50 bits

Class 2

78 bits

50 1323 4

Convolutional Code

378 78

Tail Bits

378 78

Convolutional Coding

130

Control Channel Encoding

• Control Channel Encoding

– Block of 184 bits received by BTS

– Bits are protected by Cyclic Codes of ClassFire Codes

– Adds 40 Parity Bits

– 4 Tail Bits are added

– Convolution Coding is done

• O/p from 184 Signalling bits is 456 bits.

131

Control Channel Coding

184

Coding

18440

Parity Bits


456

456 bits

4TB

132

Data Channel Coding

240

184


488

4

Punctuate

456













28

163

Supplementary Services - Call Hold

1. Call in Progress

2. Put on Hold

3. Calls another Mobile

164

Supplementary Services -Call Forwarding

IncomingCall

Voice Mail

System

PSTNPhone

AnotherMobile

Divert if

•All Calls

•Busy

•Not Reachable

•No Answer

165

Supplementary Services

• Calling Line Identification

– Present

– Absent

• Connect Line Identification

– Present

– Absent

• Closed User Group - CUG

– Only incoming

– Only outgoing

• Operator Controlled Barring

166

Voice Mail System

ANSWERING MACHINE

167

Voice Mail System

MSC

168

Short Message Service

SMSC

MSC

BTS



29

169

Short Message Service

SMSC

MSC

BTS

Point to Multipoint

Point to Point

170

PRE - PAID SYSTEM

• SIM BASED

– Data on SIM – Decrements with use

– Over the air charging !!??

• NETWORK BASED

– Data secure on with the network

– Over the air re-charging – Features

• Inquiry• Warnings …..

171

172

SEPARATE GSM & WLL INFRASTRUCTER

DUAL BAND / MODEHANDEST

MSC GSM BSC

GSM BTS

PSTN FIXED LINE SWITCHCDMA BSC

CDMA BTS

CDMA BTS

GSM BTS

173

SEPARATE GSM & WLL INFRASTRUCTER

GSM + CDMA

GSMGSM

CDMA

Call Drop.Toggle to GSM

Still on GSM.Toggle to WLL

GSM

On WLL


GSMCoverage

CDMA

Coverage

Every individual is a WLL subscriber

under any and only one CDMA BTS

and is a regular sub scriber for the rest

of the GSM network in the whole of

Punjab.

The subscriber also has the advantage

of roaming within & outside the

country.

174

COMMON GSM & CDMA INFRASTRUCTER


MSC

GSM BSC

GSM BTS

PSTN

CDMA BSC CDMA BTS

A -INTERFACE

A - INTERFACE



175

IRRIDIUM

• BTS in the Sky

– LEO ~1400km – Inter Satellite Links - 22.55GHz to 23.55GHz

– L-Band (1616MHz to 1626.5 MHz)

– Band Width - 10.5MHz

– Use TDM/FDMA scheme

– World-Wide Coverage

• 60+ Now Operational

• Small Hand held terminals

• Dual Mobiles under development

176

Documents

Training Gsm Basic