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
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
