CELLULAR COMMUNICATIONSGSM/GPRS/EDGE

Groupe Speciale Mobile/Global System for Mobile

GSM Air Interface TDMA with FDD

200Khz channels with 200KHz guard bands GSM 900 has 124 carriers GMSK modulation, 270kbps per carrier Up to 8 users, 24.8kbps per user FEC reduces to 13kbps per user for voice

Physical Channel RF carrier divided into 8 slots, numbered

0..7 Timeslots carrying data

At most 8 traffic channels Control messages

At least 1 control channels More control (logical) channels Packed into RF carrier

Single Burst/Slot

Frame Structure

Trafficchannels

(TCH)

Signalingchannel

TCH/F: Full-rate Traffic ChannelTCH/H: Half-rate Traffic Channel

FCCH: Frequency correctionSCH: SynchronizationBCCH: Broadcast control

PCH: PagingAGCH: Access grantRACH: Random access

SDCCH: Stand-alone dedicated control

SACCH: Slow associated controlFACCH: Fast associated control

Two-way

Base-to-mobile

Two-way

Logical Channel List

BCH

CCCH

DCCH

Broadcast Control Channels

Common Control Channels

Dedicated Control Channels

Channel Coding

16

What is a location area (LA)? A powered-on mobile is informed of an incoming

call by a paging message sent over the PAGCH channel of a cell

One extreme is to page every cell in the network for each call - a waste of radio bandwidth

Other extreme is to have a mobile send location updates at the cell level. Paging cut to 1 cell, but large number of location updating messages.

Hence, in GSM, cells are grouped into Location Areas – updates sent only when LA is changed; paging message sent to all cells in last known LA

International Mobile Station Equipment Identity (IMEI)

Type Approval Code (TAC): 6 decimal places, centrally assigned.

Final Assembly Code (FAC): 6 decimal places, assigned by the manufacturer.

Serial Number (SNR): 6 decimal places, assigned by the manufacturer.

Spare (SP): 1 decimal place.

International Mobile Subscriber Identity ( IMSI)

Mobile Country Code (MCC): 3 decimal places, internationally standardized.

Mobile Network Code (MNC): 2 decimal places, for unique identification of mobile network within the country.

Mobile Subscriber Identification Number (MSIN): Maximum 10 decimal places, identification number of the subscriber in the home mobile network.

Mobile Subscriber ISDN Number ( MSISDN):

Country Code (CC) : Up to 3 decimal places.

National Destination Code (NDC): Typically 2-3 decimal places.

Subscriber Number (SN): Maximum 10 decimal places.

SMS SMS allowed

Two way communications of the text messages Maximum character length of 160 characters

This can change though depending on the operator or the character set used

Character sets supported are ASCII + additional European characters Unicode

First Text Was sent in December 1992, to a Vodafone device

Sent by Neil Papworth, saying “Merry Christmas” Standard

Defined by ETSI and is known as “GSM 03.40”

SMS

SMS Continued The success is SMS was never planned for! It was only ever intended as the Pager replacement,

with limited use This will explain some of the design decisions made

SMS GSM

At a defined time interval in GSM all devices will listen to a transmission. This is when a Digital Control Channel (DCCH) packet of

information is being sent across the network. These DCCH packets are used to transfer essential information

into the devices. Information like a call is in coming Paging signals from the Base stations, to work out if a handover

is needed One of these packet formats is called SMS point to point

messaging, Paging, access control channel (SPACH) This message type can be used to carry a text message.

Advantage of this method is a text message can still be delivered during a phone conversation.

SMS

SMS Packet format All data is transferred in a single DCCH SPACH

packet

SCA Service Centre Address

MR Message Reference PID Protocol Identifier

PDU Type Protocol Data Unit Type

DA Destination Address DCS Data Coding Scheme

VP Validity Period UDL User Data Length UD User Data

GPRS: General Packet Radio Service

GSM data CSD: circuit switched data Max 14kbps Similar to voice call Inefficient usage of spectrum

GPRS packet-based service Upgrade of infrastructure GGSN is a gateway to outside world SGSN is a gateway within the network

GPRS architecture

GPRS handset classes Class A

Class A terminals have 2 transceivers which allow them to send / receive data and voice at thesame time. This class of device takes full advantage of GPRS and GSM. You can be taking a call and receiving data all at the same time.

Class B

Class B devices can send / receive data or voice but not both at the same time. Generally if you are using GPRS and you receive a voice call you will get an option to answer the call or carry on.

Class CThis device only allows one means of connectivity. An example would be a GPRS data card in a laptop.

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Packet switched Upgrades the modulation scheme

From GMSK to 8-PSK Maximum speed ~59 Kb/sec per time slot, ~473.6 Kb/sec for all 8 time

slots Variable data rate – depending on the channel conditions

Defines several different classes of service and mobile terminals

Enhanced Data GSM Environment (EDGE)

EDGE enabled data mobile

Page 28

Practically achievable data rates

Theoretical rates are constrained by mobile power and processing capabilities

Most mobiles support less than the maximum allowed by standardPractically achievable

data rates

Page 29

Migration:1. High speed circuits

switched data (HSCSD)

2. Packet switched data (GPRS,EDGE)

3. Integrated packet services – possibly under different access scheme (UMTS)

GSM Migration Towards 3G

G SM 2+9.6 Kb/sec

H S C S D64 K b/sec

G P R S114 Kb /sec

E D G E384 K b/sec

U M TS2M b/sec

1999 1Q2000

2Q2000

3Q2001

4Q2002

T im eline

D ata R ate

H S C S D - H igh S peed C ircu it S witched D ataG P R S - G ene ra l P acke t R adio S ystemED G E - Enhanced D ata G SM Environm entU M T S - U niversa l M o bile Te lephone Se rvice