Slepian-Wolf coding over broadcast channels

Abstract

We discuss reliable transmission of a discrete memoryless source over a discrete memoryless broadcast channel, where each receiver has side information (of arbitrary quality) about the source unknown to the sender. When there are K=2 receivers, the optimum coding strategy using separate and stand-alone source and channel codes is to build two independent binning structures and send bin indices using degraded message sets through the channel, yielding a full characterization of achievable rates. However, as we show with an example, generalization of this technique to multiple binning schemes does not fully resolve the K>2 case. Joint source-channel coding, on the other hand, allows for a much simpler strategy (i.e., with no explicit binning) yielding a successful single-letter characterization of achievable rates for any Kges2. This characterization, which utilizes a trivial outer bound to the capacity region of general broadcast channels, is in terms of marginal source and channel distributions rather than a joint source-channel distribution. This contrasts with existing results for other multiterminal scenarios and implies that optimal schemes achieve operational separation. On the other hand, it is shown with an example that an optimal joint source-channel coding strategy is strictly advantageous over the combination of stand-alone source and channel codes, and thus informational separation does not hold