User selection methods for multiuser two-way relay communications using space division multiple access

Abstract—In this paper, we design a multiuser two-way relay system using space division multiple access (SDMA) communi-cations and devise an optimal scheduling method that maximizes the sum rate while ensuring fairness among users. To reduce the computational load at the relays, we propose rate- and angle-based suboptimal scheduling methods. The numerical results illustrate tradeoff between complexity and the performance. Specifically, when the relay has two antennas, we verify that the rate-based method can provide significant computational savings at the cost of a rate reduction of less than 4 % when compared with the optimal scheduling method. Index Terms—Space division multiple access (SDMA), multiuser communications, two-way relay systems, scheduling. I