Multiple Descriptions With Feed-Forward: A Single-Letter Achievable Rate Region

The authors study the two-channel multiple descriptions problem for an i.i.d source, with feed-forward to one or both side-decoders. They derive a single-letter achievable rate-region that strictly includes the best known rate-region for multiple descriptions without feed-forward. In point-to-point source coding, feed-forward does not improve the rate-distortion function of a discrete memory-less source. In contrast, they provide an example to show that their region can be strictly smaller than the optimal region without feed-forward. The proof of the result uses a block-Markov superposition source coding strategy.