4 General

06.313GPPDiscontinuous Transmission (DTX) for full rate speech traffic channelsTS

Discontinuous Transmission is a mechanism which allows the radio transmitter to be switched off most of the time during speech pauses for the following two purposes:

‑ to save power in the MS;

‑ to reduce the overall interference level on the air.

4.1 General organization

The overall DTX mechanism described in the present document requires the following functions:

‑ a Voice Activity Detector on the transmit side;

‑ evaluation of the background acoustic noise on the transmit side, in order to transmit characteristic parameters to the receive side;

‑ generation on the receive side of a similar noise, called comfort noise, during periods where the radio transmission is cut.

The Voice Activity Detector is defined in GSM 06.32 "Voice Activity Detector", the comfort noise functions in GSM 06.12 "Comfort Noise Aspects". Both are based partly on the speech transcoder and its internal variables, defined in GSM 06.10 "GSM Full Rate Speech Transcoding".

In addition to these functions, if the parameters arriving at the receive side are detected to be seriously corrupted by errors, the speech or comfort noise must be generated from substituted data in order to avoid seriously annoying effects for the listener. This function is defined in GSM 06.11 "Substitution and Muting of Lost Frames".

An overall description of the speech processing parts can be found in GSM 06.01 "Processing functions".

4.2 Naming convention

Clause 3 lists the definitions of terms relevant for the DTX functions, as used in this and the technical specifications mentioned above.