Diversity-multiplexing trade-off in adaptive two-way relaying

Resource allocation for symmetric half-duplex bidirectional relaying networks is considered. Various decode-and-forward (DF) based relaying strategies that efficiently exploit quantized channel state information (CSI) at the transmitters (CSIT) are investigated. Adapting the number of channel uses for each relaying phase and allocating transmit power based on limited CSIT is shown to result in a significant improvement in the diversity-multiplexing trade-off (DMT). Without a direct link between the sources, power control is instrumental to efficiently exploit CSI feedback from sources to relay, resulting in superior performance that matches corresponding upper bounds in certain cases. With direct links between the sources, it is shown that DF two-way relaying does not suffer from a diversity loss when the multiplexing gain is high, a significant improvement over the dynamic DF protocol for one-way relaying. The best DMT is achieved when each source broadcasts partial CSI to the other nodes in the network, allowing them to adapt their transmit powers.