10 Adaptive multi-rate codec homing

06.713GPPAdaptive Multi-Rate speech processing functionsGeneral descriptionTS

The GSM adaptive multi-rate speech transcoder, VAD, DTX system and comfort noise parts of the audio processing functions (see ) are defined in bit exact arithmetic. Consequently, they shall react on a given input sequence always with the corresponding bit exact output sequence, provided that the internal state variables are also always exactly in the same state at the beginning of the experiment.

The input test sequences provided in GSM 06.74 [6] shall force the corresponding output test sequences, provided that the tested modules are in their home‑state when starting.

The modules may be set into their home states by provoking the appropriate homing‑functions.

NOTE: This is normally done during reset (initialisation of the codec).

Special inband signalling frames (encoder‑homing‑frame and decoder‑homing‑frame) described in GSM 06.90 [7] have been defined to provoke these homing‑functions also in remotely placed modules.

This mechanism is specified to support three main areas:

– type approval of mobile terminal equipment;

– type approval of infrastructure equipment;

– remote control and testing for operation and maintenance.

At the end of the first received homing frame, the audio functions that are defined in a bit exact way shall go into their predefined home states. The output corresponding to the first homing frame is dependent on the codec state when the frame was received. Any consecutive homing frames shall produce corresponding homing frames at the output.