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 effective paradigm for error-resilient data compression. While previous work only considered fixed rate systems, the extension of these techniques for variable-length encoded data was previously independently proposed by the authors, Park and Miller (see Proc. of Conf. on Info. Sciences and Systems, Princeton, N.J., 1998) and by Demir and Sayood (see Proc. of the Data Compression Conf., Snowbird, U.T., p.139-48, 1998). In this paper, we describe and compare the performance of a computationally complex exact maximum a posteriori (MAP) decoder, its efficient approximation, an alternative approximate MAP decoder, and an improved version of this decoder suggested here. Moreover, we evaluate several source and channel coding configurations. Our results show that the approximate MAP technique from Park et al. outperforms other approximate methods and provides substantial error protection to variable-length encoded data