GSM

1
GSM

• Adapted from www.mobinet.gr
• EPL 657
• Topic 4

2
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

3
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

4
GSM Coverage
5
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

6
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

7
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

8
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)

9
GSM Radio Interface

10
GSM FDMA/TDMA

11
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)

12
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

13
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

14
GSM Network Architecture (1/5)
15
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

16
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

17
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 users SIM card

18
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 IDIDinfo
• usually connect to HLR

19
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

20
Evolution of GSM Platform