Iterative source and channel decoding for GSM

When transmitting speech signals, there is residual redundancy in the signal after source coding, due to the limited complexity of the coding algorithms and delay constraints. This redundancy is expressed in correlations inside one frame as well as in a time correlation of subsequent speech frames. The method of iterative channel and source decoding applied in this paper is based on exploiting this redundancy in terms of a priori knowledge of the source to improve decoding of the transmitted parameters. The used source a priori information is obtained and exploited directly on a parameter level. We show the application of this theory to a real world mobile communication system. Here GSM speech transmission was chosen, but the presented method could also he applied to any other system which leaves a certain amount of redundancy in the speech coded signal.