A codec candidate for the GSM half rate speech channel

The ANT approach for the standardisation of the GSM half rate codec is presented. The speech codec uses efficient scalar LSP quantization, joint optimization of adaptive and fixed codebook signals and works in two modes using different bit rates (5.7 and 6.15 kbit/s). The advantage of this dual mode scheme is an increase of the average error robustness without degradation of the intrinsic speech quality. The channel codec is based on rate compatible punctured codes. The channel decoder generates soft information for each decoded information bit. Bad frame detection is exclusively based on the exploitation of soft decision information. The use of error concealment at parameter level in the channel decoder as well as at signal level in the speech decoder is discussed. The complexity of speech and channel codec is 3.8 times the GSM full rate codec complexity. Subjective tests showed that the average Q-value of all test conditions is 1.7 db below the average GSM full rate Q-value