Speech decoding with error concealment using residual source redundancy

In digital mobile communication systems there is a need for error concealment techniques to reduce the subjective effects of residual bit errors which have not been eliminated by channel decoding. This contribution presents a new approach for optimum estimation of speech codec parameters. It can be applied to any speech codec standard if reliability information about the channel decoded bits is available (e.g., soft-output Viterbi algorithm-SOVA). The proposed method exploits the residual source redundancy and includes an inherent muting mechanism leading to a graceful degradation of speech quality in case of adverse transmission conditions. In the case of an error free channel, bit exactness as required by the standards can be preserved. This approach is applied here to the GSM full rate codec.