Fair Downlink Communications for RIS-UAV Enabled Mobile Vehicles

This letter considers the sub-6GHz downlink communications from base station (BS) to mobile vehicles (MVs), where reconfigurable intelligent surface enabled unmanned aerial vehicle (RIS-UAV) serves as a mobile passive relay. To achieve communication fairness, we aim to maximize the minimum throughput among all the MVs via jointly optimizing RIS passive beamforming, MV scheduling, UAV trajectory and power allocation. The formulated problem is a mixed-integer non-convex optimization problem which is intractable to solve. Hence, the original problem is divided into three subproblems, joint passive beamforming and MV scheduling optimization, power allocation optimization, and trajectory optimization, which can be solved by the successive convex approximation (SCA) method. An alternating iterative optimization algorithm of the three subproblems is proposed to obtain the suboptimal solutions. Numerical results demonstrate the remarkable throughput gain of the proposed algorithm against other benchmarks.