CSC 290e Mobile Computing

Cellular Telephone systems
1 October 2001

Reference:  Mobile Communications by Schiller
            Chapters 3/4

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Case study:                    
                    
GSM - global system for mobile communications 
      (originally: groupe speciale mobile) formed 1982
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goal: roaming throughout Europe 
      voice service compatible to ISDN and PSTN
      integration of voice and data
      
2nd generation

FDMA:
  124 carrier frequencies, 200 kHz apart
  one or more carrier freq per base station - typically 4
TDMA
  burst period: .577 miliseconds
  8 bursts grouped into a frame
  one channel is one burst period per frame

channels
  dedicated: in use by one phone
                
  common: used by phones in idle mode
          paging channel (start a call, base station to MS)
          random access channel (start a call, MS to base station)
              * access via slotted aloha
          terminate a call
          return is slotted aloha
  broadcast: synchronization channel
             frequency correction
             information: cell id, frequencies available, etc.

Localization and calling
  system always knows where user is
  same phone number valid worldwide
  HLR - home location register
      - knows current location
  VLR - visitor location register
      - currently responsible for the MS, informs the HLR
  roaming: changing VLRs with uninterrupted availability of all services
           within the network of one provider
           between two providers in one country (typically not)
           between providers in different countries


  Steps to receive/make a call:
    See Mobile Communications, p. 100 Figure 4.7
    See Mobile Communications, p. 101 Figure 4.8