GSMGlobal System for

Mobile Communications

Contents

GSM PrinciplesCellular TechnologyGSM NetworkCall ProcessingHandoffsGPRSEDGE

• Any time Anywhere• Mobility & Roaming • High capacity & subs. density• Efficient use of radio spectrum• Seamless Network Architecture• Low cost• Flexibility• Innovative Services• Standard Interfaces

MOBILE COMMUNICATION

OBJECTIVES

Public Land Mobile Network

INDIA has adopted GSM standard for PLMN.

Digital Cellular System.Operates at 900 MHz.International Roaming facility.Power class 0.8 to 20W.Cell Radius upto 35 Kms.Maximum mobility speed 250 Km/hr.

Allocated GSM Frequency Bands

GSM900 :up: 890~915MHz down: 935~960MHzduplex interval: 45MHzbandwidth: 25MHz ，frequency interval: 200KHz

GSM1800 :up: 1710-1785MHz down: 1805-1880MHzduplex interval: 95MHz ， working bandwidth: 75MHz ，frequency interval: 200KHz

EGSM900 :

up: 880~890MHz

down: 925~935MHz

duplex interval: 45MHz

bandwidth: 10MHz ，frequency interval: 200KHz

GSM1900MHz:up:1850~1910MHzdown:1930~1990MHzduplex interval: 80MHz ，working bandwidth: 60MHz ，frequency interval: 200KHz

GSM PRINCIPLES BANDWIDTH MANAGEMENT TECHNIQUES

FDMA TDMA Cellular Technology & Frequency Re-use Scheme

FDMA

Frequency Division Multiple Access Scheme

Uplink Frequency Band = (890 – 915) MHz Downlink Frequency Band = (935 – 960)

MHz Absolute Radio Freq Carrier Number

(ARFCN) Bandwidth = 915 – 890 or 960 – 935

= 25 MHz

GSMFDMA

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

TDMA

Time Division Multiple Access SchemeOne Radio Frequency = Eight Time SlotsOne TDMA Frame = Eight Time SlotsOne Time Slot = One Physical ChannelOne Time Slot Duration = 0.577 msec

GSMTDMA

8765

43

21

8765

43

21

45 MHz

Frequency

F2’F1’(Cell transmit)

F2F1(Cell Rx)

Amplitude

Typical TDMA/ FDMA frame structure

CELLULAR TECHNOLOGY

11

Cellular Technology

Cell Site

Cluster

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)

Types of Cells

OMNI CELLS SECTOR CELLS - Two Sector Cells - Three Sector Cells

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

Frequency Re-use Scheme

Frequency Re-use Scheme

CLUSTER

A CLUSTER OF CELLS

4

5

6

7

2

3

1 1 2 3 4 5 6 7

GIVEN FREQ. RESOURCE

CELLULAR MOBILE CONCEPTS

CELLULAR MOBILE CONCEPTS

CO-CHL INTERFERENCE :Interference caused by another cell/mobile using the same frequency

D

R

Co Chl Interference is a Function of “Q”the re-use ratio:

Q =D / R

Lower Q Increased Co-Chl Interference

Higher Q Reduced Co-Chl Interference

CLASSIFICATION OF CELLS

MICRO CELLMACRO CELLUMBRELLA CELL

GSM subsystems

1. Network Subsystem includes the equipments and functions related to end-to-end call.

2. Radio Subsystem includes the equipments and functions related to the management of the connections on the radio path.

3. Operations and Maintenance subsystem includes the operation and maintenance of GSM equipment for the radio and network interface.

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

BSC:BASE STATION CONTROLLER, BTS: BASE TRANSRECEIVER STATION, OSS: OPERATION AND SUPPORT SUBSYSTEM.ss

GSM Network Structure

GSM Service Area: Total area served by the combination of all member countries where a mobile can be served.

PLMN Service Area:It is one N/W area. MSC Service Area:There can many MSC/VLR

in one PLMN area.It is one Mobile Exch. Area.

Location Area: 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.

Cells

GSM PLNM SERVICE AREA

V

MSC

MSC

MSC

MSC

VLR

VLRVLR

I II

IVIII

I

GSM MSC Service Area

MSC

VLRLA1

LA2LA3

LA6LA4

LA5

GSM CELLS

MSC

VLR

LA1LA2

LA3

LA6LA4

LA5

C1C2 C3

C6 C5C4

C=CELL

GSMRelation between areas in GSM

Location AreaCellArea served by a BTS

Location AreaMSC Service AreaPLMN Service Area

GSM Service Area

28

Call Processing

Mobile To Land Call Set-up Scenario

Phases of Mobile To Land Call

• SETUP PHASE

( Mobile Originated Call- MO Call )

• RINGING PHASE

• CONVERSATION PHASE

• RELEASE PHASE

- REQUEST FOR SERVICE ( CHANNEL ) BY MS

- CM SERVICE REQUEST

- AUTHENTICATION

- CIPHERING

- SETUP MESSAGE

- EQUIPMENT VALIDATION ( EIR CHECK )

- VALIDATION AT VLR

- ASSIGNMENT

Mobile To Land Call Set-up Scenario

• SETUP PHASE

Mobile To Land Call Set-up Scenario

MSC/VLR

Call Setup message

Is the requested basic service

provisioned for the subscriber ?

Yes

No

Release Complete

message to MS

Preliminary Digit Analysis

Is the number of digits less than the

minimum expected?

Yes

Release Complete

message to MS

No 1. Check of ODB( BAOC/BOIC/ BOIC Ex HC )

2. Subscriber call barring checks ( BAOC/BOIC etc. )

ASSIGNM ENT

Land To Mobile Call Set-up Scenario

Phases of Land To Mobile Call

• Routing Analysis

• Paging

• Authentication

• Call-Setup

• Ciphering

• Call Release

( Mobile Terminating - MT Call )

Handover

Hard Handover – Break before makeSoft Handover – make before breakSofter Handover

Evolution from GSM to 3G

The GSM Growth Phases

GSM2G

HSCSD

GPRS2.5G

EDGE

3G

GSM Evolution

GPRS200 KHz carrier115 Kbps peak data rates

EDGE200 KHz carrierData rates up to 384 Kbps8-PSK modulationHigher symbol rate

UMTS5 MHz carrier2 Mbps peak data ratesNew IMT-2000 2 GHz spectrum

GSM200 KHz carrier8 full-rate time slots16 half-rate time slots

GSM GPRS EDGE UMTS

3G2.5G2G

HSCSD

HSCSDCircuit-switched data64 Kbps peak data rates

MAIN ADVANTAGES FOR OPERATORS

• More Revenue :

By providing more than a mobile connection.

Also operator can charge on the basis of type and amount of content accessed.

• Huge Potential Market for Data Sevices :

Mobile Phone and Internet, both are fastest growing technologies and GPRS is the merger of two.

• Fast Roll-out and Continuous Network Expansion :

GPRS is an integral part of GSM.

• GPRS uses excess voice capacity for data :

GPRS Packets are transmitted in short, free periods between busy hour calls.

GPRS GSM1. SUPPORTS BOTH CKT. Only circuit switched. SWITCHED as well as packet switched service.

2. MS Utilizes Automatic No re-transmission is retransmission (ARQ) at provided. data link layer to re-transmit error frames.

3. Multiple time slots can be Single time slot per user. allotted to a single user

4. One time slot can be allotted Single time slot per user. to several users.

5. Charging/ billing more complex Simple time-based billing. (Volume based, Q.O.S. based)

GPRS Vs GSM

* Communications- E-mail, fax, intranet/ internet access.

* Value added services - Information services, games, e-commerce.

* Location-based applications - Navigation, traffic conditions, airline/rail schedule, location finder.

* Vertical applications - Freight delivery, fleet management, sales-force automation

* Location sensitive A user nearing a cinema hall or Advertising - a restaurant receives flashes of advertisement

TYPICAL GPRS SERVICES

GPRS Network

HLR

Air (Um)

Gb

Gs Gr Gf

Gn

Gn Inter-PLMN

GPRS Backbone

Gp

External packet network

Gi

SGSN

EIR

BSC

MSC/ VLR

SMS- GMSC

Gd

GGSN

GGSN

Signalling and data

Signalling

EDGE Enhanced Data rates for GSM

Evolution

GPRS = General Packet Radio System

EGPRS = GPRS + EDGE modulation

What EDGE would mean to subscribers

• Streaming Applications

• Very high speed downloads

• Corporate Intranet connections

• Quicker MMS

• Video Phone

• Vertical corporate applications – Video

Conference, Remote presentations