The multiple access diamond channel with caching relays

In this paper, we study the multiple access diamond channel, where each relay has cached a part of the message intended for the destination node. It is assumed that the cached information at the two relays are independent. We propose an achievability scheme and show that the scheme of sending correlated codewords through the multiple access channel with the superposition structure proposed for the multiple access diamond channel can be easily adapted to the case where there are cached information at the relays. We further show the optimality of our proposed scheme when the channel satisfies certain conditions. Under these conditions, it is suboptimal for the source node to inform each relay the cached message of the other relay to form common data, rather it is optimal to have no common data and use the cached message at each relay to form the correlated codewords.