GSM Adapted from Acoe 422. History of GSM During the 80s, analog cellular systems experienced rapid growth in Europe, yet they were incompatible.

GSM

Adapted from www.mobinet.gr

Acoe 422

History of GSM During the 80s, analog cellular systems

experienced rapid growth in Europe, yet they were incompatible with each other

In 1982 the Groupe special mobile (GSM) was formed to study and develop a pan-European public land mobile system

Commercial service started in 1991 Although standardized in Europe, GSM is

not only a European standard

GSM Growth 1992-2002 By 1993

there were 36 GSM networks in 22 countries

Today, over 200 GSM networks are operational in 110 countries

24 Billion SMS messages are sent per month In the UK, the market for handset ring-tones is currently

worth over €87 million annually, while young adults spent €71 million on downloadable logos

GSM accounts for 72.0% of the World's digital market and 70.0% of the World's wireless market

GSM Coverage

GSM Systems Worldwide GSM was designed to be used in the

900MHz band Later on, the frequency band of 1800MHz

was allocated to facilitate a second system, similar to GSM. This system, originally called DCS1800, evolved to be essentially the same as GSM

The American-Japanese GSM version uses the 1900MHz, used to be called PCS1900

There are now 3 GSM systems: GSM 900, GSM 1800 and GSM 1900

Dual Band Network Overview DCS 1800 cells are generally coverage

limited GSM 900 cells tend to be capacity limited Implying a need for more DCS 1800 cells to

provide similar coverage to a comparable GSM 900

Uplink Band

Downink Band

Channel Spacing

Total Number of Channels

Duplex Spacing

No of Timeslots per Channel

890 - 915 MHz

935 - 960 MHz

200 kHz

124

45 MHz

GSM 900

8

1710 - 1785 MHz

1805 - 1880 MHz

200 kHz

374

95 MHz

DCS 1800

8

GSM Characteristics Benefits

Support for international roaming Distinction between user and device

identification Excellent speech quality Wide range of services Interworking (e.g. with ISDN, DECT) Extensive security features

Services Offered by GSM Services

Telephony Asynchronous & synchronous data

services (2.4/4.8/9.6 kbps) Access to packet data network (X.25) Telematic services (SMS, fax, videotext,

etc.) Many value-added features (call

forwarding, caller ID, conferencing with up to 7 participants, voice mailbox)

GSM Radio Interface

124

FDMA FDMA

TDMAFRAME n

TDMAFRAME

n+1

200 kHz 200 kHz

2 12331

25 MHz

DownlinkMS Tx

935MHz

960MHz

UplinkMS Tx

915MHz

890MHz

25 MHz

1 2 124123 Channel Channel

124 Channels x 8 Time Slots = 992 Duplex Channels

4.615 ms

TN 7

TN 6

TN 5

TN 1

TN 4

TN 3

TN 2

3

TN 0

GSM FDMA/TDMA

Channel Structure The fundamental

unit of time in the TDMA scheme is called a burst period

Eight burst periods are grouped into a TDMA frame

Traffic Channels (TCH) are defined using a 26-frame multiframe of 120ms length

Signaling Channels (SCH)

TCH/CCH Traffic Channel

A TCH is used to carry speech and data traffic In addition to the full-rate TCHs, there are also

half-rate TCHs defined to double the capacity of the system

Control Channel To help the MS find the control channels To provide information about

voice and control channel repetition cycle. parameters in the cell surrounding cells paging

To allow random access attempts by the MS

Burst The information contained in one time slot

is a burst Five types of burst are defined

Normal Burst (NB) To carry information on traffic and control

channels Frequency Correction Burst (FB)

To synchronize the frequency of the mobile Synchronization Burst (SB)

To synchronize the frames of the mobile Access Burst (AB)

For random and handover access Dummy Burst

For padding the frame

GSM Network Architecture (1/5)

BTS Base transceiver stationBSC Base station controllerBSS Base station subsystem (BTS+BSQ)MSC Mobile switching centerGMSC Gateway MSC

MS Mobile stationHLR Home location registerVLR Visited location registerEIR Equipment identity registerAUC Authentication center

BTS

BTS

BTS

MS

BSC

BSC

MS

MS

MSC

EIRAUC

HLRVLR

GMSC

PSTNISDNPDN

GSM Network Architecture (2/5) Mobile Station

Mobile Equipment Identified by the International Mobile

Equipment Identity (IMEI) Subscriber Identity Module (SIM)

Contains a unique identification number called IMSI

It is removable, thus irrespective of a specific terminal

GSM Network Architecture (3/5) Base Station Subsystem (BSS)

Base Transceiver Station (BTS) A BTS is comprised of radio transceivers,

antennas, the interface to the PCM facility BTS is the entity that connects the mobiles to

a cellular network Base Station Controller (BSC)

Its primary function is call maintenance, by deciding when to initiate a handover, changing the BTS transmitter power, etc.

A BSC is connected to a group of BTSs and manages the radio resources for them

GSM Network Architecture (4/5) Network Subsystem

Mobile Switching Center (MSC) MSC provides functions such as registration,

authentication, location updating, handovers and call routing to a roaming subscriber

Home Location Register (HLR) The HLR contains all the administrative information and

current location of each subscriber registered in the corresponding GSM network

Visitor Location Register (VLR) Contains subscription information needed for call

control, for all mobiles in the area of the associated MSC Equipment Identity Register (EIR)

EIR is a database that contains a list of all valid mobile equipment on the network

Authentication Center (AUC) Stores the secret key held in each user’s SIM card

GSM Network Architecture (5/5) Application Service Centers are responsible

for GSM network add-on services Operation and Maintenance Center (OMC)

Monitoring and control the network Usually connect with MSC, BSC, HLR, and other

service centers Short Message Service Center (SMSC)

provide short message services usually connect to MSC

Unstructured Supplementary Service Data Center (USSDC)

provide USSD service in the form of *ID*ID*info#

usually connect to HLR

Mobility Management

Location Registration Call delivery Handoff Management

Handoff is caused by: signal strength deterioration user mobility

There are two kinds of handoff: soft handoff hard handoff

There are three ways to handoff: network-controlled handoff mobile-assisted handoff mobile-controlled handoff

MS MS

Handoffmargin

BTS old BTS new

BTS old BTS new

Evolution of GSM Platform

Development o

f Radio Tech

nology

1997Basic GSM data at 9.6 kbps

1998Landline-like circuit services (HSCSD)

1999Internet-like IP packet services (GPRS)

2000More capacity when neede (GSM 384)

2001-2002New multimedia servicesMass market cost of service (IMT-2000)

Introduction of 3rd generation radio

Evolution of GSM Platform