Energy Efficiency Optimization for RIS-Assisted Uplink-NOMA UAV Network

Abstract

In this paper, we investigate the uplink non-orthogonal multiple access network from multi-user to unmanned aerial vehicle (UAV) in a direct link blocked scenario, where a reconfigurable intelligent surface (RIS) is leveraged to assist the communication between users and UAV. We formulate a non-convex fractional programming problem in order to maximize the energy efficiency of this network. To this end, we propose an alternating iterative algorithm to jointly optimize the UAV location, UAV receiving vector, RIS phase shift matrix, and user transmit power. Specifically, the UAV location is solved by the successive convex approximation, a closed-form solution for the UAV receiving vector is derived, the RIS phase shift matrix is solved by the majorization-minimization, and the user transmit power is handled by the Dinkelbach's algorithm. Simulation results reveal that the proposed schemes can significantly improve energy efficiency.