Low Complexity User Scheduling Design for Multi-Pair Two-Way Relay Channels

In this paper, we consider low-complexity user scheduling schemes for the multi-pair two-way relay channel, where L pairs of single antenna users are selected from K pairs to perform pair-wise information exchange via an N_r-antenna amplify-and-forward (AF) relay (N_r ≥ 2L - 1) with analogue network coding (ANC). We first propose a simple channel norm (CN) based scheme, which enables low-complexity implementation. Then, we propose a near-optimal user scheduling by jointly considering the pair-wise channels norms and orthogonality among all the users (CNO-A), which requires global channel state information (CSI) and centralized computation at the relay. It is noted that CNO-A scheme can achieve comparable performance as the optimal scheduling with reduced computational complexity. Finally, we propose a two-step selective CNO scheme (CNO-S), which strikes a flexible balance between complexity/CSI overhead and performance. CNO-S significantly reduces CSI overhead and computational complexity at the relay, while achieving comparable performance as the CNO-A scheme. Numerical results and complexity analysis not only show that the proposed schemes are feasible and effective, but also demonstrate their advantages over the existing schemes.