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| ==Base Station Controller== | ==Base Station Controller== | ||
| The Base Station Controller (BSC) provides the ''intelligence'' behind the BTSs. Typically a BSC has 10s or even 100s of BTSs under it's control. The BSC handles allocation of radio channels, recieves measurements from the mobile phones, controlls handovers from BTS to BTS (except in the case of an inter-MSC handover in which case control is in part the responsibility of the ]). | The Base Station Controller (BSC) provides the ''intelligence'' behind the BTSs. Typically a BSC has 10s or even 100s of BTSs under it's control. The BSC handles allocation of radio channels, recieves measurements from the mobile phones, controlls handovers from BTS to BTS (except in the case of an inter-MSC handover in which case control is in part the responsibility of the ]). A key function of the BSC is to act as a ] where many different low capacity connections to BTSs (with relatively low utilisation) become reduced to a smaller number of connections towards the MSC (with a high level of utilisation). Overall, this means that networks are often structured to have many BSCs distributed into regions near their BTSs which are then connected to large centralised MSC sites. | ||
| ==Transcoder== | ==Transcoder== | ||
Revision as of 17:40, 18 June 2004
The Base Station Subsystem (BSS) is the section of a GSM network which is responsible for actually transmitting and recieving radio signals from the mobile phone. The BSS carries out transcoding of speech channels, allocation of radio channels to mobile phones, paging and many other tasks related to the radio network.
Base Tranceiver Station
The Base Tranceiver Station or BTS is the actual transmitter and receiver of radio signals. Typically a BTS for anything other than a picocell will have several different tranceivers (TRXs) which allow it to serve several different frequencies or even several different cells (in the case sectorised base station).
Sectorisation
By using directional antennae on a base station, each pointing in different directions, it is possible to sectorise the base station so that several different cells are served from the same location. This increases the traffic capacity of the base station (each frequency can carry eight voice channels) whilst not greatly increasing the interference caused to neighboring cells (in any given direction, only a small number of frequencies are being broadcast).
Base Station Controller
The Base Station Controller (BSC) provides the intelligence behind the BTSs. Typically a BSC has 10s or even 100s of BTSs under it's control. The BSC handles allocation of radio channels, recieves measurements from the mobile phones, controlls handovers from BTS to BTS (except in the case of an inter-MSC handover in which case control is in part the responsibility of the Anchor MSC). A key function of the BSC is to act as a concentrator where many different low capacity connections to BTSs (with relatively low utilisation) become reduced to a smaller number of connections towards the MSC (with a high level of utilisation). Overall, this means that networks are often structured to have many BSCs distributed into regions near their BTSs which are then connected to large centralised MSC sites.
Transcoder
The Transcoder (TCU) is actually not fully specified as part of the standard, rather being closely linked to the BSC. The function here is to compress voice channels from the 64kb/sec ISDN standard to the 13kb/sec rate used on the air interface. However, at least in Siemens, and Nokia's architecture this is an identifiable separate system which will normally be co-located with the MSC and in some of Ericsson's systems it is integrated to the MSC rather than the BSC. The reason for these designs is that if the compression of voice channels is done at the site of the MSC, transmission costs can be reduced.
Packet Control Unit
The Packet Control Unit (PCU) is a late addition to the GSM standard. It does some of the equivalent tasks of the BSC, but for packet data. The allocation of channels between voice and data is controlled by the base station, but once a channel is allocated to the PCU, the PCU takes full control over that channel.
The PCU can be either built into the base station, built into the BSC or even in some proposed architectures it can be at the SGSN site.
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