GSM Adapted from 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  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

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

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)

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

Evolution of GSM Platform