A NOMA-enabled Hybrid RIS-UAV-aided Full-Duplex Communication System

Abstract

In this paper, we investigate non-orthogonal multiple access (NOMA) enabled multiuser wireless communication network which uses a hybrid aerial full-duplex (FD) transmission consisting of a reconfigurable intelligent surface (RIS) mounted over an FD unmanned aerial vehicle (UAV) relay to assist the information transfer from the base station to all GUs simultaneously. We consider three different transmission modes: 1) FD-UAV-aided transmission, 2) RIS-aided transmission, and 3) joint RIS-FD-UAV transmission. Firstly, the joint passive beamforming (i.e., passive phase shift matrix) and position optimization problem is formulated to maximize the considered network’s achievable sum rate. Due to the coupling of optimization variables, the optimization problem becomes non-convex. Therefore, we utilize the block coordinate descent method to split the optimization problem into two sub-problems. We then use the Riemannian conjugate gradient (RCG) method and propose an algorithm to determine the optimal passive beamforming. Next, an iterative algorithm is proposed to obtain the optimal RIS/UAV coordinates. Finally, using both RCG and iterative algorithms, we jointly optimize the passive beamforming of RIS and the position of RIS/UAV. The effectiveness of the proposed algorithms is verified through extensive computer simulations.