A low complexity physical-layer network coding scheme for cellular two-way relaying systems

In this paper, we consider transceiver design for multiuser cellular two-way relay network (cTWRC), where a multi-antenna base station (BS) exchanges information with multiple single-antenna mobile stations (MSs) with the help of a multi-antenna relay station (RS). We propose a low complexity two-way relaying scheme for cTWRC via signal space alignment. In our scheme, the precoders at the BS and MSs are jointly designed that the two data streams delivered to and from the same MS fall in the same spatial direction at the RS. With such signal space alignment, interference-free physical-layer network coding can be performed at the relay. We analyze the end-to-end sum bit error rate (BER) performance of the proposed scheme and investigate the optimal power allocation at the BS and RS to improve the BER performance. Numerical results demonstrate that our scheme is superior to the existing amplify-and-forward based signal alignment schemes.