Pre-coding for multi-user physical network coding over a flat fading channel

The physical-layer network coding (PNC) is very attractive, since it takes full advantages of interference signals at the relay node, therefore improves the channel capacity significantly. However, the flat fading channel would destroy the sum signal received at relay node, leading to detection error and capacity damage. In this paper, a pre-coding scheme for the multi-user PNC (MU PNC) is proposed, to make the modulated signal from different source nodes holding the same phase rotation when received by the relay node, so that to eliminate the mutual interferences. The theoretical and simulation analysis indicate that the pre-coding can improve the symbol error rate (SER) performance as well as capacity, meanwhile it also simplifies the structure of receiver at relay node.