An Optimal Power Allocation for Two-Way Relay Channel Using Physical-Layer Network Coding

Physical-Layer Network Coding (PNC) is the expanding of Network Coding (NC) in wireless communication. It has enhanced throughput, spectrum efficiency and robustness of wireless communication system to a large extent. This paper considers four kinds of asymmetric two-way relay channel model based on physical-layer network coding, and analyzes their corresponding outage probability performance respectively, showing the downlink channel has more influence on the communication performance compared with the uplink channel. Furthermore, based on two different principles of minimizing outage probability and maximizing sum-rate, we derive power allocation strategies and their closed-form expressions, respectively. Simulation results show that these schemes are superior to uniform power allocation. When targeting the outage probability, the allocation strategy is a segmented function, which is judged by channel fading, the simulation results coincide with the theoretical ones. Meanwhile, compared with hypothesis testing strategy, our allocation strategy has obvious advantages to adapt to the change of channel conditions. In terms of the sum-rate, in comparison with uniform power allocation, about 2~3 dB power gain can be obtained.