Joint source-channel decoding for variable-length encoded data by exact and approximate MAP sequence estimation

Joint source-channel decoding based on residual source redundancy is an eff ective paradigm for error-resilient data compression. While previous work o nly considered fixed-rate systems, the extension of these techniques for va riable-length encoded data was recently independently proposed by the autho rs and by Demir and Sayood. In this letter, we describe and compare the per formance of a computationally complex exact maximum a posteriori (MAP) deco der, its efficient approximation, an alternative approximate decoder, and a n improved version of this decoder suggested here. Moreover, we evaluate se veral source and channel coding configurations. The results show that our a pproximate MAP technique outperforms other approximate methods and provides substantial error protection to variable-length encoded data.