Chapter 9 existing wireless systems 2g gsm system
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Chapter 9: Existing Wireless Systems: 2G, GSM System. Associate Prof. Yuh-Shyan Chen Dept. of Computer Science and Information Engineering National Chung-Cheng University. Introduction. Global System for Mobile communication or Groupe Speciale Mobile (GSM) communication

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Chapter 9: Existing Wireless Systems: 2G, GSM System

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Chapter 9:Existing Wireless Systems:2G, GSM System

Associate Prof. Yuh-Shyan Chen

Dept. of Computer Science and Information Engineering

National Chung-Cheng University


  • Global System for Mobile communication or Groupe Speciale Mobile (GSM) communication

    • Initiated by European Commission

    • Second-generation mobile cellular system

      • Aimes at developing a Europe-wide digital cellular system

    • Created in 1982 to have a common European mobile telephone standard that would formulate specifications for a pan-European mobile cellular radio system operating at 900 MHz

    • The main objective of GSM is to remove any incompatibility among the systems by allowing the roaming phenomenon for any cell phone


  • It also supports speed transmissions between MSs, emergency calls, and digital data transmission

  • Specific functions of different constituents are as follows

    • Base Station Controller (BSC):

    • Mobile Switching Center (MSC):

    • Authentication Center (AC):

    • Equipment Identity Register (EIR):

  • GSM infrastructure

    Frequency Bands and Channels

    • GSM has been allocated an operational frequency from 890 MHz and 960 MHz

      • MSs employ 890 MHz to 915 MHz

      • BS operates in 935 MHz and 960 MHz

    • GSM follows FDMA and allows up to 124 MSs to be serviced at the same time

      • The frequency band of 25 MHz is divided into 124 frequency division multiplexing (FDM) channels, each of 200 kHz (Fig. 10.9)

      • A guard frame of 8.25 bits is used between any two frames transmitted either by the BS or the MS

    Frequency band used by GSM

    GSM uses a variety of multiplexing techniques

    • GSM uses a variety of multiplexing techniques to create a collection of logical channels

    • Three control channels are used for broadcasting some information to all MSs

      • Broadcast control channel (BCCH)

      • Frequency correction channel (FCCH)

      • Synchronization channel (SCH)

    Channel in GSM


    • Three common control channels are used for establishing links between the MS and the BS

      • Random access channel (RACH):

        • Used by the MS to transmit information regarding the requested dedicated channel from GSM

      • Paging channel:

        • Used by the BS to communicate with individual MSs in the cell

      • Access grant channel:

        • Used by the BS to send information about timing and synchronization


    • Three dedicated control channels are used

      • Slow associated control channel (SACCH):

      • Stand-alone dedicated control channel (SDCCH):

      • Fast associated control channel (FACCH):

    Frames in GSM

    • GSM system uses the TDMA scheme with a 4.615 – ms long frame

      • Dividing into eight time slots each of 0.557 ms

      • Each frame measured in terms of time is 156.25 bits long, of which 8.25 period bits are guard bits for protection

      • The 148 bits are used to transmit the information

      • The frame contains 26 training bits allow the receiver to synchronize itself

      • Many such frames are combined to constitute multiframes, superframes, and hyperframes

    Frame structure of TDMA

    Identify Numbers used by a GSM System

    • International Mobile Subscriber Identity (IMSI)

    Format of IMSI


    • Subscriber Identify Module (SIM)

      • Every time the MS has to communicate with a BS, it must correctly identify itself.

      • A MS does this by storing the phone number, personal identification number for the station, authentication parameters, and so on in the SIM card

      • Smart SIM cards have a flash memory

      • The main advantage of SIM is that is supports roaming with or without a cell phone, also called SIM roaming

  • Mobile System ISDN (MSISDN)

  • Format of MSISDN


    • Location Area Identify (LAI)

      • The GSM service area is usually divided into a hierarchical structure that facilitates the system to access any MS quickly

      • Each PLMN is divided into many MSCs

      • Each MSC typically contains a VLR to tell the system if a particular cell phone is roaming

      • If it is roaming, the VLR of the MSC in which the cell phone is reflects the fact

      • Each MSC is divided into many location areas (LAs)

      • A location area is a cell or a group of cells and is useful when the MS is roaming in a different cell but the same LA


    • Since any LA has to be identified as the part of the hierarchical structure

    • The identifier should contain the country code, mobile network code, and LA code

    GSM layout


    • International MS Equipment Identity (IMSEI)

    Format of IMSEI


    • MS Roaming Number (MSRN)

    Format of MSRN

    Layout, Planes, and Interfaces of GSM

    Interface of GSM


    • The GSM system can be divided into five planes

      • OAM

      • CM

      • MM

      • RR

      • Physical

    Functional planes in GSM


    • Authentication is done with the help of a fixed network that is used to compare the IMSI (International Mobile Subscriber Identity) of the MS reliably

    Authentication process in GSM

    Handoff in GSM

    • Intracell/intra-BTS handoff

    • Intercell/intra-BSC handoff

    • Inter-BSC/intra-MSC handoff

    • Inter-MSC handoff

    Inter-MSC handoff

    Personal Communication Service (PCS)

    • PCS employs an inexpensive, lightweight, and portable handset to communicate with a PCS BS

    • The PCS is classified into high-tier and lower-tier standards

    • High-tier system includes high-mobility units with large batteries

      • An MS in a car

    • Low-tier system includes system with low mobility, capable of providing high-quality portable communication service over a wide area

    • The PCS lower-tier standards based on PACS (Personal Access Communication Systems) and DECT (Digital European Cordless Telecommunication) are given in Table 10.6.

    FCC view of PCS

    PCS High-Tier Standards

    PCS Low-Tier Standards

    Chronology of PCS Development

    • CT2 (Cordless Telephone)

      • Using FDMA with a speed rate of 32 kbps using Adaptive Differential Pulse Code Mudulation (ADPCM)

      • The transmitter data rate is 72 kbps

      • Uses TDD, which allows BS and MS share one channel

      • D is called D-channel which includes 4 bits of control information

  • DECT (Digital European Cordless Telecommunication)

  • CT2 TDD Slot (First Generation)

    DECT (Digital European Cordless Telecommunication)

    • The second-generation cordless telephone system

    • DECT operates on frequencies ranging from 1880 MHz to 1900 MHz

    • Uses ADPCM with 32 kbps speed rate

    • Uses TDD with two frames with 10-ms periods

    • Supports both voice and data transmission

    DECT TDD Slot (Second Generation)

    Bellcore View of PCS

    • The Bellcore view of PCS is based on five different service provided between the Bellcore client company (BCC), BCC network, and the PCS wireless provider network

      • PCS access service for networks (PASN)

        • A connection service to and from the PCS service provider (PSP)

      • PCS access service for controllers (PASC)

        • A service for use with PCS wireless provider (PWP) across radio channels and some type of automatic link transfer capability

    Bellcore View of PCS

    • PCS access service for ports (PASP)

      • An interface into PWP

    • PCS access service for data (PASD)

      • A database information transport service

    • PCS access service for external service providers (PASE)

      • Is used to support specialized PCS service like voice mail and paging

    Bellcore PCS Architecture


    System 7

    Radio Port

    Radio Port

    Control Unit

    Operation, Administration,

    & Maintenance

    Description of the PCS Air Interface:Forward TDMA Frame for PCS

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