Instantaneous relaying with bit-interleaved coded modulation: Design and optimization

In this paper, we combine bit-interleaved coded modulation (BICM) with instantaneous relaying for the three-node relay channel. We propose a two-step optimization: The first step optimizes the relay functions for different instantaneous relaying strategies like sawtooth (ST) relaying and constellation rearrangement (CR) relaying in order to provide the highest amount of mutual information to the destination. The second step focuses on the bit-to-symbol mapping with the purpose to maximize the achievable gain from iterative demapping/decoding. As our results show, a significant gain can be obtained by using ST and CR relaying with optimized mappings compared with conventional amplify-and-forward and detect-and-forward relaying and compared with standard mappings optimized for point-to-point communications.