Distributed User Scheduling for MIMO-Y Channel

In this paper, distributed user scheduling schemes are proposed for the multi-user MIMO-Y channel, where three N_T-antenna users (N_T = 2N, 3N) are selected from three clusters to exchange information via an NR-antenna amplify-and-forward (AF) relay (N_R = 3N), and N ≥ 1 represents the number of data stream(s) of each unicast transmission within the MIMO-Y channel. The proposed schemes effectively harvest multi-user diversity (MuD) without the need of global channel state information (CSI) or centralized computations. In particular, a novel reference signal space (RSS) is proposed to enable the distributed scheduling for both cluster-wise (CS) and group-wise (GS) patterns. The minimum user-antenna (Min-UA) transmission with N_T = 2N is first considered. Next, we consider an equal number of relay and user antenna (ER-UA) transmission with N_T = 3N, with the aim of reducing CSI overhead as compared to Min-UA. For ER-UA transmission, the achievable MuD orders of the proposed distributed scheduling schemes are analytically derived, which proves the superiority and optimality of the proposed RSS-based distributed scheduling. These results reveal some fundamental behaviors of MuD and the performance-complexity tradeoff of user scheduling schemes in the MIMO-Y channel.