An improved physical layer network coding scheme for two-way relay systems

In this paper we consider a two-way relaying system with two sources A, B and one relay R, where the two sources desire to exchange information through the relay. The transmission consists of two states: multiple access (MAC) stage, where A and B transmit the channel-coded signals to R simultaneously, and broadcast (BC) stage, where R transmits towards both A and B. One critical process at R is to decode the superimposed signal from A and B in such a way that A and B could decode the information from each other reliably at the BC stage. Instead of decoding the individual information belonging to A and B separately, R aims to decode the superimposed signal to the network-coded combination of the two source information, i.e., the binary XOR of the two source information. We refer this decoding process as the joint channel decoding and physical network encoding (JCNC). In this paper, a novel iterative decoding algorithm is presented for the physical network coding scheme, which is applicable to any linear channel code, e.g. Low-Density Parity-Check (LDPC) code. Furthermore, the two-way relaying scheme is extended to distributed multiple input multiple output (MIMO) multi-hop networks. Based on an antenna selection criterion within each virtual antenna array (VAA), the end-to-end (e2e) BER of the multi-hop system can be further reduced. Simulation results show that the proposed scheme outperforms other recently proposed network coding schemes with slightly increased complexity.