BSNL

An Overview ON BSNL SUMMER TRAINING

SUBMITTED BY-

RAJAN MEENA

08EC071 VII SEM (ECE)

BSNL OBJECTIVESOBJECTIVES

The Cellular Concept

The GSM Access Network

The GSM Core Network

BSNL Communication - Mobile

TelephoneExchange

SubscriberLine (2W)

Inter-ExchangeJunction

Mobile SwitchingCentre (MSC)

BSC BTSMS

BSNL

CELLULAR MOBILE CONCEPTS

WHAT IS A CELL ?

• A base station (transmitter) having a number of RF channels is called a cell

• Each cell covers a a limited number of mobile subscribers within the cell boundaries ( Coverage area)

• Typical Cell Radius Aprrox = 30 Km (Start up), 1 KM (Mature)

BSNL

Voice Channels Coverage area

Forward path

Reverse path

Or control

channels

Lines toBSC

MS

A RADIO CELL

BSNL Fundamental problems

• Radio range, or coverage

• No. of channels, or voice circuits

• Full, seamless service coverage

• Large no. of subscribers in the range of millions

BSNL

FERQUENCY SCARCITY PROBLEM

TelEx.

WIRED NETWORK

100,000 50 Khz = 5 Ghz (NOT POSSIBLE)

Hence Individual RF Loop is not extended

But a Common group of channels is shared

CELLULAR MOBILE CONCEPTS

BW for Telephony speech: 3KHz increases to 25 KHz with FM for Radio Trans.

BSNL GSM Specifications

Carrier Separation - 200 kHz

No. of RF Carriers - 124

Access Method -TDMA/FDMAModulation Method -

GMSKTransmission Rate -270.833 KbpsSpeech Coding - Full rate 13 Kbps

Half rate 6.5 Kbps

Duplex Distance - 45 MHz

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GSM FDMA(Frequency Division Multiple Access

25 MHz 25 MHz

Mobile to Base

0 1 2

890.2 890.4 890.6(MHz)

Base to Mobile

0 1 2

935.2 935.4 935.6

200 kHz45MHz

Channel layout and frequency bands of operation

890 935 960915

200 kHz

BSNL

GSM TDMA(Time Division Multiple Access)

8765

43

21

8765

43

21

45 MHz

Frequency

F2’F1’(Cell transmit)

F2F1(Cell Rx)

Amplitude

Typical TDMA/ FDMA frame structure

BSNL

FDMA/TDMA Scheme

BP1

BP2

BP3

BP4

BP5

BP6

BP7

BP8

BP1

BP2

TIME

890.0

890.2890.4

890.6890.8

891.0891.2 915.8

FREQ

MHz

BURSTF

R

A

M

E

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LOGICAL CHANNELS• USER INFORMATION( TRAFFIC)• SIGNALLING INFORMATION (CONTROL)

GSM RF CHANNELS

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Network Architecture

BTS

MSC VLR

HLR

PSTNISDN

DataNetworks

Air interface

OSS

BTS

BTS

MSC VLR

BSCBSC

1 MSC=16 BSC

1 BSC=1024 TRU

A Interface

A-bis interface

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GSM Network Structure• GSM Service Area: Total area served by the

combination of all member countries where a mobile can be served.

• MSC Service Area: There can many MSC/VLR in one PLMN area.It is one Mobile Exch. Area.

• GMSC: All I/C calls for PLMN N/W will be routed through GMSC. In a GSM/PLMN N/W all mobile terminated calls will be routed to a Gateway MSC. Call connections between PLMNs , or to fixed N/Ws must be routed to a GMSC.The GMSC contains the Inter working functions to make these connections.

• Location Area• Cells

BSNL

LOCATION AREA : There are several LA in a MSC/VLR combination. A LA is a part of the MSC/VLR service area in which a MS may move freely without updating location information to the MSC/VLR exchange that control the LA. Within a LA a paging message is broadcast in order to find the called mobile subs. LA can be identified by system using the LAI.

CELL : A cell is an identity served by one BTS. The MS distinguishes between cells using the BASE STATION IDENTIFICATION CODE(BSIC) that the cell site broadcast over the air.

GSM Network Structure

BSNL

MSC/VLR

MSC/VLR

MSC/VLR

MSC/VLR

II

I

IIIIV

GSMPLMN Service Area

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MSC/VLR

LA 1 LA 2

LA 6

LA 3

LA 4

LA 5

GSMMSC Service Area

BSNL

MSC/VLR

LA 1 LA 2

LA 6

LA 3

LA 4

LA 5

C1

C5C4

C7

C2

C3

C6

GSMCells

C = Cell

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GSMRelation between areas in GSM

Location AreaCellArea served by a BTS

Location AreaMSC Service AreaPLMN Service Area

GSM Service Area

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GSMFunctions of Mobile Station

• Voice and data transmission

• Frequency and time synchronization

• Monitoring of power and signal quality of the surrounding cells

• Provision of location updates even during inactive state

• Equalization of multi path distortions

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GSMMobile Station

• Portable, vehicle mounted, hand held• MS identified by unique IMEI(International Mobile Equipment

Identity)

• Shell display at least last ten received, dialled and missed calls

• Minimum talk time of 1hr 30 min. and standby time of 80 hrs

• 160 characters long SMS

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GSMMobile Identification Numbers

IMEI

MSISDN

IMSI

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GSM IMSI

• International mobile subscriber’s Identity

• The IMSI is an unique identity which is used internationally and used within the network to identify the mobile subscribers.

• The IMSI is stored on the subscriber identity module (SIM), the HLR, VLR and AC database.

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RSSRSS

n BTS n BTS

BSC

BSC

BSC

MSC/VLR

RADIO SUB SYSTEM (RSS)

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GSMFUNCTION OF BTS -I

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

• Transcoding and rate adaption Functionality• Time and frequency synchronisation signals

transmission.• 11 power classes from .01 watts to 320 watts

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GSMFUNCTION OF BTS -II

• Frequency hopping

• Random access detection

• Uplink radio channel measurements

• BTS mainly consists of a set of transceivers (TRX).

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GSMFUNCTIONS OF BSC-I

• It is connected to BTS and offloads MSC

• Radio resource management

• Inter-cell handover

• Reallocation of frequencies

• Power control

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GSMFUNCTIONS OF BSC-II

• Time delay measurement of the received signals from MS with respect to BTS clock.

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

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GSMMSC-BSS Configurations

BTSBTS

BTS

A-bisBSC

BSS

Configuration -6 Multi - cell site = multi--BTS site

Many single cell sites

BSS

MSC

BTS

AA

A

Single - cell siteConfiguration -1

Multi - cell site (sector CellsConfiguration -5

MSC: Mobile Switching Centre

BSS: Base Station System

BSC: Base Station Controller

BTS: Base Transceiver Station

A-bis

BTS BTS

BTS

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GSMMSC ( MOBILE SWITCHING CENTRE)

Manages communication between GSM & other network

Call setup functions, basic switching are done

MSC takes into account the RR allocation in addition to normal exchange functions

MSC does gateway function while its customers roams to other network by using HLR /VLR

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GSMMSC Functions - I

Paging, specifically call handling

Location updation

Handover management

Billing for all subscribers based in its area

Reallocation of frequencies to BTSs in its area to meet

heavy demands

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GSMMSC Functions - II

Echo canceller operation control Signaling interface to databases like HLR, VLR. Gateway to SMS between SMS centers and subscribers

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GSMVISITOR LOCATION REGISTER (VLR)-I

It controls those mobiles roaming in its area.

VLR reduces the number of queries to HLR

One VLR may be incharge of one or more LA.

VLR is updated by HLR on entry of MS its area.

IMSI detach and attach operation

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GSM Home Location Register(HLR)-I

• Reference store for subscriber’s parameters, numbers, authentication & Encryption values.

• Current subscriber status and associated VLR.

• Both VLR and HLR can be implemented in the same equipment in an MSC.

• One PLMN may contain one or several HLR.

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GSM Home Location Register(HLR)-II

Data stored is changed only by man-machine.

Category of MS ( whether pay phone or not )

Roaming restriction ( allowed or not ).

Supplementary services like call forwarding

Permanent data in HLR

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Temporary data in HLR The data changes from call to call & is

dynamic

VLR address, MSC address.

Messages waiting data used for SMS

GSM Home Location Register(HLR)-II

BSNL