Design and Analysis of BICM-ID for Two-Way Relay Channels With Physical-Layer Network Coding

This paper proposes a general iterative demapping- decoding approach for two-way relay (TWR) communications with physical-layer network coding, where the relay node performs decode-and-forward. The bit-interleaved coded modulation (BICM) with high-order quadrature amplitude modulation is considered. The iterative decoding, namely the BICM-ID for TWR channels, is introduced. Based on a joint trellis, BICM-ID estimates the end nodes' coded bits, leading to an estimation of the transmitted symbol pair probability, which is crucial for achieving iterative decoding gains in bit error rate (BER). The end nodes' constellation design criterion is proposed to optimize the BICM-ID performance over the TWR fading channel. The EXtrinsic Information Transfer analysis is also performed, showing the iterative system's convergence behavior and providing information on code design. Our simulation results show the proposed BICM-ID scheme can achieve significant performance gains, yielding an asymptotic tendency of approaching the cut-set BER performance limit.