SNR‐based selective relaying schemes in network‐coded two‐way relay channels

Abstract

In this study, for a network-coded two-way relay channel (TWRC), the authors propose three different relaying schemes that satisfy certain quality of service requirements at both transceivers. In these schemes, the relay decides independently whether to help each transceiver or not based on the instantaneous signal-to-noise ratios received from the transceivers. Under the assumption of error propagation, they analyse the performance of the system in terms of the end-to-end bit error rate (BER), the outage probability , the average spectral efficiency (ASE) and the diversity order. All of these performance measures depend on two thresholds employed by the relay node. By optimising these thresholds under three different criteria, they achieve three different relaying schemes: (i) the BER­ optimal scheme that minimises the end-to-end BER; (ii) the outage-constrained scheme that minimises the end-to­ end BER under an outage probability constraint; and (iii) the BER-constrained scheme that maximises the ASE under an end-to-end BER constraint. The analysis of the system shows that the BER-optimal scheme guarantees the full diversity gain at both transceivers; the outage-constrained scheme results in a bidirectional relaying scheme with a constant outage probability; and the BER-constrained scheme makes use of spectrum as efficiently as possible while maintaining the target BER.