06.413GPPDiscontinuous Transmission (DTX) for half rate speech traffic channelsTS
For the purposes of the present document, the following terms and definitions apply:
accepted SID frame: traffic frame which is flagged with SID= "1" or SID= "2" by the Radio Subsystem.
bad traffic frame: traffic frame flagged BFI= "1" (Bad Frame Indication) or with UFI= "1" (Unreliable Frame Indication) by the Radio Subsystem.
frame: time interval of 20 ms corresponding to the time segmentation of the half rate speech transcoder defined in GSM 06.20 (ETS 300 969) ), also used as a short term for a traffic frame.
good speech frame: good traffic frame which is not an accepted SID frame.
good traffic frame: traffic frame flagged BFI= "0" and UFI= "0" by the Radio Subsystem.
GS averaging period: period in which the quantized energy tweak parameters GS are averaged: it corresponds to the hangover period.
hangover period: period of 7 frames added at the end of a speech burst in which VAD flag = "0" and SP flag= "1".
invalid SID frame: accepted SID frame which was not classified as valid SID frame. This frame is not valid for updating comfort noise parameters, but the frame conveys information that comfort noise generations should be started or continued.
lost SID frame: unusable frame received when the RX DTX Handler is generating comfort noise and a SID frame is expected (Time Alignment Flag TAF= "1").
lost speech frame: unusable frame received when the RX DTX Handler is passing on traffic frames directly to the speech decoder.
SID code word: fixed bit pattern defined in GSM 06.22 , for labelling a traffic frame as a SID frame.
SID field: bit positions defined in GSM 06.22 , of the SID codeword within a SID frame.
SID frame: frame characterised by the SID (Silence Descriptor) code word. It conveys information on the acoustic background noise.
SP flag: boolean flag, generated by the TX DTX handler, indicating the presence of a speech frame ("1") or the presence of a SID frame ("0").
speech frame: traffic frame that cannot be classified as a SID frame.
traffic frame: block of 112 information bits transmitted on the half rate speech traffic channel.
unusable frame: bad traffic frame that is not an accepted SID frame.
VAD flag: boolean flag, generated by the VAD algorithm defined in GSM 06.42 , indicating the presence ("1") or the absence ("0") of a speech frame.
valid SID frame: good traffic frame flagged with SID= "2" by the Radio Subsystem. This frame is valid for updating comfort noise parameters at any time.
For the purposes of the present document, the following symbols apply:
GS Energy tweak parameter
Nelapsed Number of elapsed frames since the last updated SID frame
For the purposes of the present document, the following abbreviations apply:
BFI Bad Frame Indicator
BSC Base Station Controller
BSS Base Station System
DTX Discontinuous Transmission
FACCH Fast Associated Control CHannel
FEC Forward Error Correction
GSM Global System for Mobile communications
MS Mobile Station
RSS Radio Sub System
SACCH Slow Associated Control CHannel
SID SIlence Descriptor
TAF Time Alignment Flag
UFI Unreliable Frame Indicator
VAD Voice Activity Detector
For abbreviations not given in this clause, see GSM 01.04 .