User Scheduling and Height Optimization in UAV-Assisted Maritime XL-MIMO Communications

As an important part of the space-air-ground-sea integrated communication networks, unmanned aerial vehicles (UAVs) and unmanned surface vehicles (USVs) have recently garnered considerable attention. In this paper, we consider the UAV-assisted user scheduling and height optimization in the maritime extremely large-scale multiple-input-multiple-output system. To improve the achievable sum-rate, we focus on reducing inter-channel interference by optimizing the USV positions and the UAV-base station (BS) height. Specifically, we derive a set of orthogonal positions in the near-field region of the uniform rectangular array such that the channels of the USVs located at that positions are orthogonal to each other. Based on the orthogonal positions, we propose a joint optimization algorithm that provides a suboptimal orthogonal position assignment scheme for the USVs and optimizes the UAV-BS height. Simulation results verify the effectiveness of the proposed orthogonal position and the joint optimization algorithm.