Joint encoding and node-pair grouping for physical-layer network coding

Physical-layer network coding (PNC) is a promising technique to improve the performance of wireless networks. In a traditional setting, two packets are encoded with PNC. However, encoding three or more packets with PNC may further enhance the performance. A straightforward method to achieve multiple packet encoding is to further process the superposed signal from different source node-pairs at the relay, and broadcast a jointly encoded packet to the destinations. After receiving the jointly encoded packet, each destination can decode the packet it intends to receive, based on the packet transmitted by itself and overheard packets from other node-pairs. An important issue that arises is how to determine which node-pairs should be encoded together and how to jointly encode these packets. This paper aims to solve this issue. We first propose a joint encoding method for multiple node-pairs, and then propose a method to determine the grouping of different node-pairs so that node-pairs in the same group can perform joint encoding. The proposed scheme is not restricted to a particular signal constellation, and, in principle, it can be applied to any type of signal constellations. Simulation results show that the proposed scheme can bring throughput improvement compared to schemes which only encode two packets together, the resulting throughput is also close to the optimum.