Sum-Rate Maximization for UAV Relay-Aided Fluid Antenna System with NOMA

Fluid Antenna System (FAS), Non-Orthogonal Multiple Access (NOMA), and Unmanned Aerial Vehicle (UAV) have been explored as promising technologies for sixth-generation (6G) wireless networks. However, a single technology alone will not be sufficient to meet the stringent performance requirements of 6G. Thus, in this paper, we propose a NOMA-based UAV Relay-Aided FAS to address this challenge. Specifically, we jointly optimize the active port, power allocation, and UAV altitude to maximize the achievable sum-rate of Ground Users (GUs) while satisfying minimum rate requirements. To tackle this non-convex optimization problem, we decouple it into two sub-problems: a large-scale fading optimization problem and a small-scale fading optimization problem. We demonstrate that the large-scale fading problem can be solved using a one-dimensional search method, while the small-scale fading problem can be addressed with closed-form expressions. Our simulation results show that FAS consistently outperforms Traditional Antenna System (TAS). Moreover, the combination of FAS and NOMA greatly benefits from the joint optimization of both small-scale and large-scale fadings in UAV relay-aided communications, resulting in substantial performance improvements over the existing TAS and Orthogonal Multiple Access (OMA) combination.