5 Transcoding/rate adaption and multiplexing

08.523GPPBase Station Controller - Base Tranceiver Station (BSC-BTS) Interface - Interface PrinciplesTS

The interface supports two options: transcoding/rate adaption performed in BTS or outside BTS.

5.1 Transcoding/rate adaption in BTS

The transcoding of speech to normal 64 kbit/s A-law is performed within BTS.

Data may be rate adapted or submultiplexed to 64 kbit/s circuits.

5.2 Transcoding/rate adaption outside BTS

In this case the transcoder/rate adaptor is considered as part of the BSC.

The channel coding/decoding is performed by BTS/TRX. The choice of coding/interleaving has to be signalled from BSC to BTS.

The remote speech transcoder has to have knowledge of some radio parameters for an efficient decoding. In addition, the timing of the transcoder has to be aligned with the transmission of the frames over radio such that the frames from BSC arrive synchronized with the transmission over radio (minimizes delay due to remote transcoder). For this control and time alignment of the transcoder, inband signalling is used within a 16 kbit/s or an 8 kbit/s channel carrying speech or data, signalling and synchronisation. This remote control of the transcoder is specified in Technical Specifications 3GPP TS 08.60 (full rate traffic channels, 16 kbit/s submultiplexing only) and 3GPP TS 08.61 (half rate traffic channels, 16 or 8 kbit/s submultiplexing).

For data, rate adaption to subrate 16 or 8 kbit/s is performed within BTS.

For the link BTS-BSC, the following possibilities are foreseen:

– rate adaption of 16 kbit/s or 8 kbit/s speech + control or 16 kbit/s data + control to 64 kbit/s (one radio traffic channel per 64 kbit/s terrestrial channel),

– multiplexing of 16 kbit/s or 8 kbit/s speech + control or 16 kbit/s or 8 kbit/s data + control into one 64 kbit/s channel (up to eight radio traffic channels per 64 kbit/s terrestrial channel).