19-02-2013, 10:28 AM
GLOBAL SYSTEM FOR MOBILE COMMUNICATION
GLOBAL SYSTEM.ppt (Size: 1.75 MB / Downloads: 25)
Components of the network (1)
BTS, base transceiver station
consists of all radio relevant parts of network
functions for physical layer (modulation, coding, frequency hopping, time MUX)
transparent for most of upper layer messages
average size: 9 transceivers
BSC, base station controller
first time specified unit in cellular networks
decrease load of MSC (otherwise on MSC: high processor load, low switching capacity)
fast processing of handovers
administration of BTSs
average size: >350 transceiver = 38 BTSs
GSM system features overview
International mobility: roaming, billing
Fully digital system
Security: IMSI / TMSI, extensive security mechanisms
Low subscription costs
Commercially:
- liberalization of telcos,
- service provider licensing,
- warehouse sales
Economics:
- provider competition, better price & quality
Environment:
- power control, FDMA + TDMA, DTX
Roaming
The roaming feature allowas an user to make and receive calls in any GSM network and to use his specific services worldwide.
Roaming agreement between operators required!
Example “VIAG”: subscriber is managed as Swisscom subscriber in non-covered areas => D1, D2 or Eplus network is used!
New speech codecs
TFO (Transcoder (or Tandem) Free Operation):
avoids transcoding and associated quality losses in mobile-to-mobile calls
when both mobiles of a speech-connection are using the same voice codec, the coding and transcoding in the BSS is switched of
GSM news: CTS
CTS = Cordless Telephony
Systems:
a home base station is connected to the fixed extension line (i.e. PTSN)
advantage: costs
disadvantage: mobile has to support it (=> SW upgrade?)