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 recently independently proposed by the authors [6], [7] and by Demir and Sayood [1]. In this paper, we describe and compare the performance of a computationally complex exact maximum a posteriori (MAP) decoder [6], [7], its efficient approximation [6], [7], an alternative approximate MAP decoder [1], 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 [6], [7] outperforms other approximate methods and provides substantial error protection to variable-length encoded data.