Robust transmission of variable-length encoded sources

Digital communications systems commonly use compression (source coding) and error control (channel coding) to allow efficient and robust transmission of data over noisy channels. When compression is imperfect, some residual redundancy remains in the transmitted data and can be exploited at the decoder to improve the decoder's probability-of-error performance. A new approach to joint source-channel maximum a posteriori probability (MAP) decoding applicable to systems employing variable-length source codes (VLCs) was previously developed by the authors-the resulting joint decoder's structure is similar to that of the conventional Viterbi decoder. This paper extends the authors' previous work to address the problem of error propagation, an inherent problem with using VLCs. Options considered include list decoding, trellis-pruning, and composite schemes. Simulation results presented show that the proposed techniques can result in significant improvement in decoding performance.