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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

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):
frequency bands and channels
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
gsm uses a variety of multiplexing techniques
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)
  • 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
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
identify numbers used by a gsm system
Identify Numbers used by a GSM System
  • International Mobile Subscriber Identity (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)
  • 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
  • International MS Equipment Identity (IMSEI)
  • MS Roaming Number (MSRN)
  • The GSM system can be divided into five planes
    • OAM
    • CM
    • MM
    • RR
    • Physical
  • 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
handoff in gsm
Handoff in GSM
  • Intracell/intra-BTS handoff
  • Intercell/intra-BSC handoff
  • Inter-BSC/intra-MSC handoff
  • Inter-MSC handoff
personal communication service pcs
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.
chronology of pcs development
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)
dect digital european cordless telecommunication
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
bellcore view of pcs
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 pcs1
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
Bellcore PCS Architecture


System 7

Radio Port

Radio Port

Control Unit

Operation, Administration,

& Maintenance