On the capacity of bidirectional relaying with unknown varying channels

One key feature to improve the performance of future wireless communication systems will be the use of relays. In this work, we consider the bidirectional relay channel, where a relay node establishes a bidirectional communication between two nodes, and study coding strategies for the case of unknown varying channels. In the first phase of a decode-and-forward protocol the two nodes transmit their messages to the relay node, which decodes them. In the succeeding bidirectional broadcast phase the relay broadcasts a re-encoded composition of them so that both nodes can decode the intended message using their own message from the previous phase as side information. We assume that the whole communication is affected by unknown varying channels. For both phases we present the capacity regions and characterize the impact of channel uncertainty on the achievable rates. Thereby, it shows that the unknown variation can lead to channels which completely prohibit a reliable communication.