Full-diversity-achieving incremental relaying in network-coded two-way relay channels

In this paper, for a network-coded two-way relay channel (TWRC), we propose a spectrally-efficient incremental relaying scheme that eliminates redundant relay transmissions such that the error propagation phenomenon is effectively mitigated and the full diversity gain is achieved at both transceivers. We analyze the performance of the system in terms of the end-to-end bit error rate (BER), the average spectral efficiency (ASE) and the diversity order. All of these performance measures depend on a single threshold employed by the destination. We optimize this threshold such that the end-to-end BER is minimized. The asymptotic analysis of the system shows that the proposed scheme by employing the BER-minimizing threshold guarantees the full diversity gain at both transceivers. Moreover, the ASE tends to its maximum achievable value in the high-SNR regime. We also propose a class of geometry-independent thresholds that asymptotically perform the same as the optimal threshold. The simplicity of these thresholds makes the system very attractive from a practical standpoint.