Time-Asynchronous Gaussian Multiple Access Relay Channel with Correlated Sources

Abstract

We study the transmission of a set of correlated sources $(U_1,\cdots,U_K)$ over a Gaussian multiple access relay channel with time asynchronism between the encoders. We assume that the maximum possible offset ${\mathsf{d_{max}}}(n)$ between the transmitters grows without bound as the block length $n \rightarrow \infty$ while the relative ratio ${{\mathsf{d_{max}}}(n) / n}$ of the maximum possible offset to the block length asymptotically vanishes. For such a joint source-channel coding problem, and under specific gain conditions, we derive necessary and sufficient conditions for reliable communications and show that separate source and channel coding achieves optimal performance. In particular, we first derive a general outer bound on the source entropy content for all channel gains as our main result. Then, using Slepian-Wolf source coding combined with the channel coding scheme introduced in \cite{Cover_McEliece:81} on top of block Markov coding, we show that the thus achieved inner bound matches the outer bound. Consequently, as a corollary, we also address the problem of sending a pair of correlated sources over a two user interference channel in the same context.