1. GSM Adapted from www.mobinet.gr Acoe 422

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 user’s 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 *ID*ID*info#  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