On the simultaneous relay channel with collocated relay and destination nodes

The simultaneous relay channel with collocated relay and destination nodes is investigated. This models the scenario in which the source user is unaware of the channel controlling the communication but it knows the set of all possible relay channels. Our primary focus is the case where the relay node is physically near to the destination so that Compress-and-Forward (CF) coding is the adequate cooperative strategy. A broadcasting scheme for flexible user cooperation is developed. This enables the encoder to send part of the information regardless of which channel is present and additional information intended for each of the different channels. It can be seen that this problem is equivalent to that of sending common and private information to several destinations in presence of helper relays. This scenarios is identified as the broadcast relay channel (BRC). A general achievable rate region is derived and specific results are obtained for the case of Gaussian BRCs. The advantage of the proposed coding scheme is that the source can adapt its coding rate to the different channels that might be present during the communication.