Outage analysis and power allocation for space-time block coded two-way relaying systems

In this paper, we consider the three-node two-way relay channel (TWRC) over which communication is performed using space-time block codes (STBC) with physical-layer network coding (PNC) protocol. Two end nodes simultaneously communicate with each other over a relay node where each node is equipped with two antennas and uses Alamouti´s STBC to provide diversity. First, a closed form expression for the outage probability of the STBC-TWR system is derived, assuming nonreciprocal channels, equal transmit power at each node and decode-and-forward (DF) strategy at the relay. It is shown that the STBC-TWR system significantly improves the uncoded TWRC outage performance. Then, to further improve the performance, an optimal power allocation to maximize the sum-rate under the total power constraint, is proposed. It is shown that the optimal power allocation considerably improve the sum-rate as well as the outage performance compared to the equal-power case.