LDPC coded DBICM Scheme for Two Way Relay Channel with a Pipeline Decoding Structure

Abstract

Low-density parity-check (LDPC) coded bit inter-leaved coded modulation (BICM) is a bandwidth efficient coded modulation scheme and has been successfully employed in the two-way relay channel (TWRC). However, LDPC-BICM scheme does not take the correlations between coded bits from the same modulated symbol into account so that it cannot achieve the maximum a-posteriori (MAP) decoding performance. The later proposed BICM with iterative decoding scheme or the joint channel and physical-layer network coding scheme indeed consider the correlations and improve the error correction performance, but suffer from implementation issues of higher computational complexity and larger latency. In this paper, we propose an LDPC-Delayed BICM (DBICM) scheme to make a successful tradeoff between the performance and the complexity. To this end, we add a delay module between the encoder and the modulator to introduce correlations between codewords. Based on it, we propose a pipeline decoding structure and feed back the decoding result of a codeword to the demodulator as the a priori information for the next codeword. The proposed LDPC-DBICM scheme thus can utilize the correlations without increasing latency too much. We verify the effectiveness of our proposed scheme by theoretical mutual information analysis and finite-length simulations.