Joint Source Channel Coding for Discrete Memoryless Channels
joint source/channel; Maximum A Posteriori (MAP); Maximum Likelihood (ML); decoding
The design of optimal joint source/channel coding and decoding is examined for disÂ crete memoryless channels with endÂtoÂend distortion as the criterion for reliable comÂ munication. Joint source/channel encoders which map sequences of source symbols directly to sequences of channel symbols without any intermediate "bit" representaÂ tion of source are considered. Optimum joint source/channel decoder that minimizes endÂtoÂend distortion for a given encoder mapping is derived. The encoder mapping can be many to one, in the sense that many source sequences can be mapped to one sequence of channel symbols. To begin with, as an exercise, random coding bound on endÂtoÂend distortion is derived for a general Maximum A Posteriori (MAP) decoder which has some estimate on the apriori probabilities of source symbols. It is shown that, the KL distance of the actual apriori probabilities with the estimated ones plays an important role. Then, a random coding bound on endÂtoÂend distortion is derived with our optimal minimum distortion decoder mentioned above for the case when all source symbols are equally likely. It is shown that the performance increase with minÂ imum distortion decoding as opposed to MAP (same as Maximum Likelihood (ML) decoding in this case when all source symbols are equally likely) is characterized by the faster decay of endÂtoÂend distortion with respect to channel use.
MetadataShow full item record
- ECE Publications