Joint Beamforming, Power Control, and Trajectory Planning for NOMA-Based UAV Relaying System

Next-generation wireless communication networks are expected to support a large number of connections and full coverage capabilities. Unmanned aerial vehicle (UAV) and non-orthogonal multiple access (NOMA) techniques can be adopted due to their ability to expand the coverage area and enhance system capacity. In this paper, we propose an innovative NOMA-based UAV relaying system, where a UAV equipped with multiple antennas acts as a relay to provide service for multiple ground users. To address the rate fairness issue, we aim to maximize the minimum achievable sum rate among all users by jointly solving the problem of beamforming design, power control, and UAV trajectory planning subject to the power budget, QoS requirements as well as the UAV flight trajectory constraints. We then propose an alternating optimization algorithm based on successive convex approximation (SCA) and semidefinite relaxation (SDR) methods to jointly optimize the beamforming and power variables while dynamically controlling the UAV trajectory, thereby achieving reliable UAV relaying transmission. Simulation results demonstrate that, compared with the baseline designs, the proposed algorithm achieves a substantial improvement in the minimum achievable sum rate with satisfactory efficiency. Moreover, simulations reveal that the considered system tends to be interference-limited under stringent QoS requirements, especially when there is non-negligible residual interference caused by imperfect successive interference cancellation (SIC).