MOBILE COMMUNICATION

GSM

WHAT IS MOBILITY ?

• Access the Technology everywhere whether we are work or play, in the office, grounds or at home. To meet this demand the GSM (Global System for Mobile Communication) for mobile telephony was introduced in the mid-1980s. A boom is underway, such that many GSM user find life without their phone practically inconceivable.

MOBILE COMMUNICATION

CDMATDMA/FDMA

Evolution Chart

Years

Service type

Multimedia

VoiceAnalog

AMPS

Digital

IS 95 IS

136 GSM

IMT 2000

Wireless Internet Mobile system

~ 24kbps ~64kbps ~2Mbps ~20Mbps

1980 1990 2000 2010

1G 2G 3G

4G

Narrow Band Wide Band

Broad Band

Time Time Time

Freq

Freq

Freq

PN Code

FDMA TDMA CDMA

FDMA ( FREQUENCY DIVISION MULTIPLE ACCESS )

• In FDMA, the entire allocated cellular frequency spectrum is divided into a number of 30-kHz channels .

• The power transmitted by a cell is only large enough to communicate with mobile stations located near the edge of the cell’s coverage area.

• The radius of a cell might be one mile or less-referred to as a small cell

TDMA (TIME DIVISION MULTIPLE ACCESS)

• TDMA is a digital wireless air interface .

• It divides each carrier frequency into a number of time slots, each of which constitutes an independent telephone circuit.

CDMA (CODE DIVISION MULTIPLE ACCESS)• A digital multiple access technique specified

by the Telecommunications Industry Association (TIA) as "IS-95."

• One of the unique aspect of CDMA is that while there are certainly limits to the number of phone calls that can be handled by a carrier, this is not a fixed number .

• Code division multiple access (CDMA) is a digital air interface standard, claiming eight to fifteen times the capacity of analog.

GSM IS A TDMA TECHNIQUE

HISTORY OF GSM

•GSM: Global System for Mobile Communications•Formerly: Group Special Mobile

When ?• 1982: GSM created to set

standard.• 1988: Industrial development

started.• 1991: First Systems Deployed.

What ?

Why ?

•Higher digital voice quality. •Low cost alternatives to making calls such as SMS. •Ability to deploy equipment from different vendors.

GSM Services

• Tele-services• Bearer or Data Services • Supplementary services

Tele Services

• Telecommunication services that enable voice communication via mobile phones

• Offered services- Mobile telephony- Emergency calling

BEARER SERVICES

• Short Message Service (SMS) o up to 160 character alphanumeric data

transmission to/from the mobile terminal• Unified Messaging Services(UMS)• Group 3 fax• Voice mailbox• Include various data services for information

transfer between GSM and other networks like PSTN, ISDN etc at rates from 300 to 9600 bps

• Electronic mail

SUPPLEMENTARY SERVICES Call related services :

• Call Waiting- Notification of an incoming call while on the handset

• Call Hold- Put a caller on hold to take another call• Call Barring- All calls, outgoing calls, or incoming

calls• Call Forwarding- Calls can be sent to various

numbers defined by the user• Multi Party Call Conferencing - Link multiple calls

together• CLIP – Caller line identification presentation• CLIR – Caller line identification restriction• CUG – Closed user group

GSM ARCHITECTURE

SYSTEM ARCHITECTURE Mobile Station (MS):

Base Station Subsystem (BSS):

Network Subsystem:

• Mobile Equipment (ME)

• Subscriber Identity Module (SIM)

• Base Transceiver Station (BTS)• Base Station Controller (BSC)

• Mobile Switching Center (MSC)• Home Location Register (HLR)• Visitor Location Register (VLR)• Authentication Center (AUC)• Equipment Identity Register (EIR)

MOBILE STATION (MS)

• The Mobile Station is made up of two entities:

• Mobile Equipment (ME)o The Mobile Equipment is the

hardware used by the subscriber to access the network .

o Uniquely identified by an IMEI (International Mobile Equipment Identity)

o Subscriber Identity Module (SIM)o Smart card containing the

International Mobile Subscriber Identity (IMSI)

o Allows user to send and receive calls and receive other subscribed services

o Protected by a password or PIN

BASE STATION SUBSYSTEM

Base Station Subsystem is composed of two parts :

1) Base Transceiver Station (BTS) 2) Base Station Controller (BSC)

• Base Transceiver Station (BTS)

Houses the radio transceivers that define a cell

Handles radio-link protocols with the Mobile Station

• Base Station Controller (BSC)

Manages Resources for BTSHandles call set upLocation updateHandover for each MS

NETWORK SUBSYSTEM Mobile Services Switching Center (MSC) Major MSC Functions :

Switching and call routing Charging Service provisioning Communication with HLR Communication with the VLR Communication with other MSCs Control of connected BSCs Direct access to Internet services

Home Location Registers (HLR) : Contains administrative information of

each subscriber Most important database

Visitor Location Registers (VLR) - Integrated with MSCo tracks which customers have the phone on and

ready to receive a callo periodically updates the database on which

phones are turned on and ready to receive callsAuthentication Center (AUC)

o mainly used for securityo data storage location and functional part of the

networko Ki is the primary element

Equipment Identity Register (EIR) - Database that is used to track handsets using

the IMEI ,Made up of three sub-classes: The White List, The Black List and the Gray List

o Optional database

GSM FREQUENCY ALLOCATION• GSM systems use radio frequencies

between 890-915 MHz for receive and between 935-960 MHz for transmit.

• RF carriers are spaced every 200 kHz, allowing a total of 124 carriers for use.

• An RF carrier is a pair of radio frequencies, one used in each direction.

• Transmit and receive frequencies are always separated by 45 MHz

890 960935915

UPLINK FREQUENCIES DOWNLINK FREQUENCIES

UPLINK AND DOWNLINK FREQUENCY SEPARATED BY 45MHZ

Downlink

Uplink

GSM SECURITY

GSM Security MS

NETWORK

A3 A8 A3 A8

EqualSRES

Kc

Ki KiRandom no

Ki Ki

SRESKc

• On air interface, GSM uses encryption and TMSI instead of IMSI.

• SIM is provided 4-8 digit PIN to validate the ownership of SIM

• 3 algorithms are specified :- A3 algorithm for authentication- A5 algorithm for encryption- A8 algorithm for key generation

EXPLANATION