INTRODUCTION TO GSM

1 . 1 I n t r o d u c t i o n Global System for Mobile Communication (GSM) is a set of

ETSI standardsspecifying the infrastructure for a digital cellular service. The standard is used inapprox. 85 countries in the world including such locations as Europe, Japan andAustralia. [001] Figure 1.1: The Simple Representation of GSM Network [065]GSM is worldwide standard that allows users of different operators to connectand to shares the services simultaneously. GSM has been the backbone of thephenomenal success in mobile telecommunication over the last decade. Now, atthe dawn of the era of true broadband services, GSM continues to evolve to meetn e w d e m a n d s . O n e o f G S M ' s g r e a t s t r e n g t h s i s i t s i n t e r n a t i o n a l r o a m i n g capability, giving consumers a seamless service in about 160 countries. This hasbeen a vital driver in growth, with around 300 million GSM subscribers currentlyin Europe and Asia. In the Americas, today's 7 million subscribers are set to growrapidly, with market potential of 500 million in population, due to the introductionof GSM 800, which allows operators using the 800 MHz band to have access toGSM technology too. [002]

Global System for Mobile Communication (GSM) The Europeans realized this early on, and in 1982 the Conference of EuropeanPosts and Telegraphs (CEPT) formed a study group called the Groupe SpcialMobile (GSM) to study and develop a panEuropean public land mobile system.The proposed system had to meet certain criteria: good subjective speech quality, low terminal and service cost, support for international roaming,

ability to support handheld terminals, support for range of new services and facilities spectral efficiency, and ISDN compatibility. [003]GSM is a standard for a Global System for Mobile communications. GlobalSystem for Mobile communications, a mobile phone system based on multipler a d i o c e l l s ( c e l l u l a r m o b i l e p h o n e n e t w o r k ) . I t h a s b e e n a g r e e d u p o n a n d i s completed by ETSI, the European Telecommunications Standards Institute . 1.2Two Main Standards of GSM Two main standards are followed:1.GSM 900 (global system for mobile communications in the 900 MHz band)2.DCS 1800 (digital cellular system for the 1800 MHz band)GSM 900 is a designed for extensive radio coverage even in rural areas. DCS1800 is designed for radio coverage in areas with very high subscriber density.GSM is a global standard, GSM 900 being used in most European, Asian and p a c i f i c c o u n t r i e s , G S M 1 8 0 0 b e i n g u s e d i n t h e s a m e p l a c e t o i n c r e a s e t h e capacity of the system, and GSM 1900 being used primarily in the US.In its simplest form, Global System for Mobile Communication (GSM) is a set of ETSIstandards specifying the infrastructure for a digital cellular service. TheEurope, Japan and Australia.The international designation of a public mobile radio network is PLMN (publicl a n d mobile network), as opposed to the PSTN (public switc hed t e l e p h o n e network).S e v e r a l P L M N , w h i c h a r e d e s i g n e d o n t h e b a s i s o f s a m e s t a n d a r d s , a r e compatible to each other. Therefore, a mobile subscriber can use the GSM/DCSs p e c i f i c m o b i l e e q u i p m e n t a n d s e r v i c e s i n t h e s e c o m p a t i b l e n e t w o r k s . [ ] Hutchison Whampoa Limited 1.4Specifications and Characteristics for GSM Frequency band the frequency range specified for GSM is 1,850 to 1,990 MHz (mobile station to base station). Duplex distancethe duplex distance is 80 MHz. Duplex distance is thedistance between the uplink and downlink frequencies. A channel has twofrequencies, 80 MHz apart. C h a n n e l s e p a r a t i o n t h e s e p a r a t i o n b e t w e e n a d j a c e n t c a r r i e r frequencies. In GSM, this is 200 kHz. ModulationModulation is the process of sending a signal by changingt h e c h a r a c t e r i s t i c s o f a c a r r i e r f r e q u e n c y . T h i s i s d o n e i n G S M v i a Gaussian minimum shift keying (GMSK). Transmission rateGSM is a digital system with an over-the-air bit rateof 270 kbps. Access method GSM utilizes the time division multiple access (TDMA)concept. TDMA is a technique in which several different calls may sharethe same carrier. Each call is assigned a particular time slot. Speech coder GSM uses linear predictive coding (LPC). The purpose of LPC is to reduce the bit rate. The LPC provides parameters for a filter thatmimics the vocal tract. The signal passes through this filter, leaving behinda residual signal. Speech is encoded at 13 kbps. [006], [007], [008], [009],[010]

2 . 1 G S M N e t w o r k A r e a s The GSM network is made up of geographic areas. As shown in Figure, theseareas include cells, location areas (LAs), MSC/VLR service areas, and public land mobile network (PLMN) areas. Figure 2.1: Network Areas [011] 2.1.1Cell Cell is the basic service area. The cell is the area given radio coverage by onebase transceiver station. The GSM network identifies each cell via the cell globalidentity (CGI) number assigned to each cell. 2.1.2Location Area The location area is a group of cells. It is the area in which the subscriber is paged. Each LA is served by one or more base station controllers, yet only by asingle MSC. Each LA is assigned a location area identity (LAI) number.