Joint Resource Allocation and Beamforming Design for MU-MIMO Relay Networks

Sidelink relay technique is an effective technique for coverage enhancement and data rate improvement, which has recently achieved success in diversified wireless applications. The main bottleneck of applying sidelink to multiple-user multiple-input multiple-output (MU-MIMO) system is how to overcome interference among user equipments (UEs). In this paper, we consider an MU-MIMO relay network with both downlink and uplink UEs, where sidelink reuses the same resources of uplink UEs. To maximize the sum rate of downlink UEs, we propose a novel joint resource block allocation and beamforming design algorithm for the considered MU-MIMO relay network. Specifically, we first formulate an optimization problem with the constraint on the sum-rate degradation of uplink UEs. However, the formulated mixed integer nonlinear programming problem is NP-hard. In order to solve this problem, we first relax the discrete variables and then transform the continuous problem into a convex one based on the weighted minimum mean square error (WMMSE) algorithm. Meanwhile, we prove the equivalence between the aforementioned two problems. Finally, we utilize the block coordinate descent method to solve the transformed problem and obtain the resource block allocation and beamforming design. Simulation results validate the effectiveness of the proposed algorithm and demonstrate the importance of joint optimization.