Generalised selection at multi-antenna sources in two-way relay networks

A generalised selection transmission (GST) and generalised selection combining (GSC) scheme is proposed for two-way relay networks where two multi-antenna sources exchange information via a single-antenna relay. New exact and asymptotic expressions are derived for the outage probability and symbol error rate (SER) in Rayleigh fading. Moreover, a tight upper bound on the ergodic sum-rate is presented. These results are used to demonstrate that the proposed GST/GSC scheme preserves the full diversity order, which equals the minimum number of antennas at the two sources. It is also shown that the impact of the number of selected antennas lies in the array gain only. Furthermore, the GST/GSC scheme significantly improves the performance relative to single-antenna selection, and only incurs a negligible reduction in performance relative to all-antenna beamforming. Finally, the optimal relay location that minimises the SER is determined analytically. It is observed that the optimal relay location shifts towards one source when the number of selected or available antennas at the other source increases.