5th European Conference on Speech Communication and Technology

Rhodes, Greece
September 22-25, 1997

Robust GSM Speech Decoding Using the Channel Decoder's Soft Output

Tim Fingscheidt, Olaf Scheufen

Institute of Communication Systems and Data Processing, Aachen University of Technology, Aachen, Germany

In the digital mobile radio system GSM (Global System for Mobile Communications) there is a need for reducing the subjective effects of residual bit errors by error concealment techniques. Due to the fact that the standard does not specify these algorithms bit exactly, there is room for new solutions to improve the decoding process. This contribution presents a new approach for optimum estimation of speech codec parameters [7] applied to the GSM system. It requires a soft-output channel decoder (e.g. soft-output Viterbi algorithm -- SOVA [8]) providing a bit reliability information for the proposed parameter estimation process. Additionally, a priori knowledge about the residual redundancy in the sequence of codec parameters is exploited. The new method includes an inherent muting mechanism leading to a graceful degradation of speech quality in case of adverse transmission conditions. If the channel is error free, bit exactness as required by the GSM standard is preserved.

Full Paper   Acoustic Example #1   Acoustic Example #2  

Bibliographic reference.  Fingscheidt, Tim / Scheufen, Olaf (1997): "Robust GSM speech decoding using the channel decoder's soft output", In EUROSPEECH-1997, 1315-1318.