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