3 Definitions, symbols and abbreviations

06.223GPPComfort Noise Aspects for Half Rate Speech Traffic ChannelsTS

3.1 Definitions

For the purposes of the present document, the following terms and definitions apply.

frame: time interval of 20 ms corresponding to the time segmentation of the half rate speech transcoder, also used as a short term for a traffic frame.

H(Z): combination of the short term (spectral) filter A(z) and the spectral weighting filter W(z).

SID codeword: fixed bit pattern for labelling a traffic frame as a SID frame.

SID field: bit positions of the SID codeword within a SID frame.

SID frame: frame characterized by the SID (Silence Descriptor) codeword. It conveys information on the acoustic background noise.

SP flag: speech flag.

speech frame: traffic frame that cannot be classified as a SID frame.

VAD flag: Voice Activity Detector flag.

W(Z): spectral weighting filter of the GSM half rate speech codec.

Other definitions of terms used in the present document can be found in GSM 06.20 [2] and GSM 06.41 [3]. The overall operation of DTX is described in GSM 06.41 [3].

3.2 Symbols

For the purposes of the present document, the following symbols apply:

GS Energy tweak parameter.

R0 Frame energy value.

R(i) Unquantised (normalized) autocorrelation sequence.

rj Optimal reflection coefficient.


SUM ( x(n) ) = x(a) + x(a+1) + …. + x(b‑1) + x(b); (Accumulation).


GSP0 codeword Vector quantization index, joint vector quantization of the parameters GS and P0.

P0 Power contribution of the first excitation vector as a fraction of the total excitation power at a subframe.

3.3 Abbreviations

For the purposes of the present document, the following abbreviations apply:

AFLAT Autocorrelation Fixed Point LAttice Technique (used in the GSM half rate speech codec for the vector quantization of the LPC coefficients)

BSS Base Station System

DTX Discontinuous Transmission

ETS European Telecommunication Standard

GSM Global System for Mobile communications

MS Mobile Station

RX Receive

SID SIlence Descriptor

TX Transmit

VAD Voice Activity Detector

VQ Vector Quantization

For abbreviations not given in this clause, see GSM 01.04 [1].