GSM SYSTEM
#1

PRESENTED BY:-
Upendra Kumar
Vinit Kumar Barnwal
Badal Chandra Pandey
Madan Kumar

[attachment=9504]
GSM SYSTEM
GSM introduction
Evolution of cellular telephony

PSTN : PSTN Call Setup
PSTN : PSTN Call Setup
Cordless telephony
Cellular Telephony
Frequency reuse in cellular telephony
Evolution of GSM Standards
1980s
Advanced Mobile Phone Service ( AMPS ), in America.
Early 1980s
European nations were developing cellular solutions, but no common standard available.
1982
CEPT ( Conference of European Posts and Telegraph ) formed a study group called the Groupe Special Mobile ( GSM ).
Evolution of GSM Standards
Objective of GSM
Good speech quality.
Low terminal and service cost.
Support for international roaming.
Ability to support handheld terminals.
Support for range of new services and facilities.
Spectral Efficiency.
ISDN Compatibility.
Evolution of GSM Standards
 1989
GSM responsibility transferred to ETSI ( European Telecommunications Standards Institute ).
Global System for Mobile Communication.
 1990
Phase I of GSM Specifications published.
 Mid 1991
Commercial services started.
 1997
Commercial services available in 110 countries.
Services provided by GSM
Tele-service : Telephony.
Data Service :
Circuit Switched data upto 9600 bps.
G3 Fascimile.
SMS ( Short Message Service ).
Supplementary Service.
Call Forwarding, when subscriber unavailable.
Call Barring for O/g or I/c calls.
Caller Identification.
Call Waiting.
Multiparty Conversation.
GSM
Network elements
GSM Network Elements
GSM Element : Mobile Station.
Consists of the Mobile Equipment & SIM Card.
Mobile Equipment
Uniquely identified by IMEI ( International Mobile Equipment Identity ).
SIM ( Subscriber Identity Module ).
Uniquely identified by IMSI ( International Mobile Subscriber Identity ).
Also contains a secret key for Authentication.
Can be protected against unauthorized use by a PIN ( Personal Identity Number ).
Can also store SMS messages for later retrieval.
IMSI & IMEI are independent ( personal mobility ) .
GSM Element : Mobile Station
GSM Element ( Base Station Subsystem )
BSS ( Base Station Subsystem ).
BTS ( Base Transceiver Station ).
Radio Transceivers.
Handles Radio Link Protocols with the MS.
BSC ( Base Station Controller ).
Manages the radio resources for one or more BTS.
Handles Radio Channel Setup, Frequency Hopping, Handovers.
GSM Element ( HLR )
Contains administrative information of each subscriber registered in the corresponding GSM network.
Location of the mobile is typically in the form of the signaling address of the VLR associated with the Mobile Station.
Important data fields
MSISDN ( Mobile Subscriber ISDN No. ).
Present VLR.
IMSI ( International Mobile Subscriber Identity ).
GSM Element ( VLR )
Contains selected administrative information from the HLR, necessary for call control and provision of the subscriber services, for each mobile currently located in the geographical area controlled by the VLR.
GSM Element ( EIR )
Database of all valid mobile equipment in the network ( IMIE ).
Three Lists corresponding to the status of the equipment.
White List.
Grey List.
Black List.
GSM Element ( AuC )
Protected database that stores a copy of a secret key number.
Number used for authentication and encryption.
GSM : Location Updation.
GSM Network : Call Routing.
Air Interface
GSM
Normal Burst Period Structure.
Frame Structure.
Hyperframe & Superframe
Burst Types.
Normal Burst.
Carry data.
F Burst.
Used in FCCH ( Frequency Correction Channel ).
S Burst.
Used in SCH ( Synchronization Channel ).
Access Burst.
Used in RACH ( Random Access Channel ).
Dummy Burst
Burst Types
Logical Channel Types
Traffic Channels
TCH/F
Traffic Channel Full Rate
@13 Kbps
TCH/H
Traffic Channel Half Rate
@6.5 Kbps
EFR
Enhanced Full Rate
@13 Kbps
Broadcast Channels Downlink
BCCH
Broadcast Control Channel
Broadcasting Network / cell specific information
FCCH
Frequency Correction Control Channel
Used by the mobiles for frequency correction
SCH
Synchronization Channel
Synchronize mobiles ( TDMA FN & BSIC )
CBCH
Cell Broadcast Control Channel
Common Control Channel
Downlink
PCH
Paging Channel
For alerting mobiles
AGCH
Access Grant Channel
For granting access to mobile
Uplink
RACH
Random access channel
Mobiles seeking attention of the BTS
Dedicated Control Channel
 Slow
◦ SACCH
 Slow Associated Control Channel ( duplex )
 Transmission of signaling data ( radio page link supervision meas., transmit power control, timing advance )
 Fast
◦ SDCCH
 Standalone Dedicated Control Channel ( duplex )
 Signaling channel used for service request
◦ FACCH
 Fast Associated Control Channel
 Stealing flag and preemption
 Used during call setup, handover
Radio Link Aspects.
ITU Allocation for GSM 900
Band 890 - 915 Mhz for Uplink ( MS to BSS ).
Band 935 - 960 MHz for Downlink ( BSS to MS ).
To maximize the capacity utilization,
Access Technique is FDMA / TDMA / FDD.
25 MHz bandwidth divided into
124 Carriers ( ARFCN ).
Spaced 200 KHz apart.
TDMA Superposed on the carrier frequencies.
Each Base Station assigned Multiple frequencies.
FDMA / TDMA
GSM 900 / GSM 1800
Multi-path Equalization
Frequency Hopping
Objective
Multi-Path Fading is dependent on carrier frequency. Changing the carrier frequency slowly, helps alleviate the problem.
Co-channel interference is in effect randomized.
Realization
The ARFCN for the channels is changed in each successive frame, based on Hopping Sequence.
Frequency Hopping
Discontinuous Transmission
Average Person speaks for 40% of the time.
Transmitter turned off during silence period.
Benefit : Minimizes Co-channel Interference.
Added Benefit : Conserves Power.
VAD ( Voice Activity Detection ):
Voice misinterpreted as noise, Clipping occurs.
Noise misinterpreted as Voice, efficiency decreases.
Comfort Noise Creation at the receiver during off period.
Discontinuous Reception.
Paging channel used for alerting mobiles.
Paging channel is structured into sub-channels.
MS to listen only to its own sub-channel.
For Power Conservation at the MS.
Power Classes ( MS ).
Five Power Classes.
For Mobile Station ( GSM 900 )
5 levels.
20 W ( 43 dBm ) : Class I.
8 W ( 39 dBm ) : Class II.
5 W ( 37 dBm ) : Class III.
2 W ( 33 dBm ) : Class IV.
0.8 W ( 29 dBm ) : Class V.
Power level can be stepped up or down in steps of 2 dB, from the peak power, for the class down to a minimum of 13 dBm (20mW).
Power Classes ( BS ).
Eight Power Classes.
For Base Station.
Eight classes.
320 W ( 55 dBm ) : Class I.
160 W ( 52 dBm ) : Class II.
80 W ( 49 dBm ) : Class III.
40 W ( 46 dBm ) : Class IV.
20 W ( 43 dBm ) : Class V.
10 W ( 40 dBm ) : Class VI.
5 W ( 37 dBm ) : Class VII.
2.5 W ( 34 dBm ) : Class VIII.
Voice Processing.
GSM Radio Link Characteristics
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