1 Lecture 19 EEE 441 Wireless And Mobile Communications

2 Global System for Mobile Communications (GSM) Designed to be a digital, wide area, wireless network Driven by European telecom manufacturers, operators, and standardization committees Presently the most popular system around the world

3 GSM Topics Structure of a GSM network Architecture of a GSM network  GSM functional entities  GSM network interfaces  GSM protocols

4 GSM Design Goals Good speech quality Low terminal and service cost Support for international roaming Ability to support handheld terminals Support for range of new services Spectral efficiency ISDN compatibility

5 GSM Statistics 205 countries use GSM System (Feb 2004) GSM accounts for 72.5% of the World's digital market and 72.0% of the World's wireless market

6 GSM Subscribers by Region

7 GSM Subscribers Growth Blue bars = in-year net gains 2001 is an estimate

8 GSM Network Overview

9 Distinctive Features of GSM Cooperative development by many players from many countries Preserved open interfaces between the subsystems Phase 1 GSM spec sections and 5,320 pages  telephony (full rate speech)  emergency calls  data transmission at 2.4/4.8/9.6 kbps transparent (i.e. error correction done by FEC) non-transparent (i.e. information retransmitted when received incorrectly)  short message service (SMS)

10 Distinctive Features of GSM (Cont’d) Phase 2  non-voice services (Advice of Charge, Caller ID, Call Waiting, Call Hold, Conference Calling, Call Forwarding/Diverting, etc)  enriched telephony (half-rate speech)  High-speed circuit-switched data (HSCSD) Phase 2.5  GPRS: Global packet radio system  Enhanced data rates for GSM (EDGE)

11 GSM Network Architecture MS: Mobile Station BSS: Base Station Subsystem MSC: Mobile Switching Center O&M: Operations and Maintenance Center VLR, HLR, AuC, EiR …

12 GSM Interfaces U m Interface  Mobile Station and base station subsystem communicate across U m interface, also known as air interface or radio link A bis interface  Base Transceiver Station (BTS) and Base Station Controller (BSC) communicate across A bis interface A interface  Base Station Subsystem (BSS) communicates with Mobile Switching Center (MSC) across A interface

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14 GSM Interfaces: Review U m Interface  Mobile Station and base station subsystem communicate across U m interface, also known as air interface or radio link A bis interface  Base Transceiver Station (BTS) and Base Station Controller (BSC) communicate across A bis interface A interface  Base Station Subsystem (BSS) communicates with Mobile Switching Center (MSC) across A interface

15 Mobile Station (MS) Mobile Equipment (ME) SIM: Subscriber Identity Module While subscriber roams or is stationary, the MS transmits a radio signal to one of the many BTS using a radio-link protocol via the U m interface

16 Base Station Subsystem (BSS) The BSS is composed of two parts:  BTS: Base Transceiver Station  BSC: Base Station Controller BTS handles:  RF interface

17 BSS (Cont’d) BSC BTS HLRVLREIRAuC MSC PSTN Um Abis A SS7 TRAU

18 Mobile Switching Center (MSC) Interface between radio system and fixed networks (PSTN and ISDN) Connected to BSS through A interface Usually an E-1, either wireline or microwave

19 MSC (Cont’d) Each MSC covers several cells (BSS)

20 MSC (Cont’d) Also performs signaling between MSC and other functional entities using SS7:  Registration  Authentication  Location updating  Handovers  Call routing to a roaming subscriber

21 Other GSM Network Entities HLR: Home Location Register VLR: Visitor Location Register EIR: Equipment Identity Register AuC: Authentication Center

22 Home Location Register (HLR) Central database for all subscribers:  Identity of the subscriber  Services accessible to the subscriber  Current location of the subscriber Each subscriber appears only once in database HLR might be physically distributed in several sites (e.g., using first two digits to identify physical HLR)

23 Visitor Location Register (VLR) Database with information on MS within area served by MSC:  MS Roaming number  Location area in which was last registered  Supplementary services Used by an MSC to retrieve information for various purposes:  Handling of calls to or from a roaming mobile station currently located in its area Typically part of MSC

24 Call Routing

25 Authentication Center (AuC) Entity associated with HLR for authentication:  allows International Mobile Subscriber Identity (IMSI) to be authenticated Allows ciphering of communication over radio path between mobile station and network Transmits data needed for authentication and ciphering from HLR to VLR and MSC

26 Equipment Identity Register (EIR) Logical entity responsible for storing International Mobile Equipment Identities (IMEIs) in network used in GSM system Equipment classified as "white listed", "grey listed” or "black listed” Ensures that MEs being used are valid and authorized to function

27 GSM Radio Transmission Combination of FDMA and TDMA Frequencies: 800, 900, 1800, 1900 MHz For example, GSM 900:  Uplink = MHz  Downlink = MHz Each 25 MHz bandwidth divided into 124 carrier frequencies spaced 200 KHz apart Each 200kHz then rotated among 8 users in TDMA fashion

28 Notices Read  Rappaport, Ch 11.3