Towards Joint Optimization for UAV-Integrated RIS-Assisted Fluid Antenna Systems

TL;DR

This work tackles downlink UAV communications under air-to-ground interference by jointly optimizing a fluid antenna system (FAS) on a UAV and a UAV-mounted RIS. By formulating a nonconvex rate-maximization problem over RIS phase shifts $\boldsymbol{\theta}$ and FA port positions $\boldsymbol{r}$, the authors develop a provably convergent SCA method that transforms the problem into a sequence of SOCPs solvable by MOSEK, with all updates performed concurrently per iteration. The approach yields rapid convergence and significant improvements in outage probability and achievable rate compared with fixed-position antennas and non-optimized baselines, particularly as the RIS size grows. The results demonstrate the practical potential of integrating UAV-mounted RIS and FAS technologies to mitigate interference and boost spectral efficiency in aerial networks, with extensions to multi-UAV scenarios and imperfect CSI highlighted for future work.

Abstract

Unmanned aerial vehicles (UAVs) integrated into cellular networks face significant challenges from air-to-ground interference. To address this, we propose a downlink UAV communication system that leverages a fluid antenna system (FAS)- assisted reconfigurable intelligent surface (RIS) to enhance signal quality. By jointly optimizing the FAS port positions and RIS phase shifts, we maximize the achievable rate. The resulting nonconvex optimization problem is solved using successive convex approximation (SCA) based on second-order cone programming (SOCP), which reformulates the constraints into a tractable form. Simulation results show that the proposed algorithm significantly improves both outage probability and achievable rate over conventional fixed-position antenna (FPA) schemes, with particularly large gains in large-scale RIS configurations. Moreover, the algorithm converges rapidly, making it suitable for real-time applications

Figures (8)

• Figure 1: Downlink interference in a cellular-UAV scenario.
• Figure 2: Schematic of a fluid antenna system with $M$ flexible ports.
• Figure 3: Outage probability versus transmit power under CSI-free scheme.
• Figure 4: Convergence behavior of SCA-Algorithm.
• Figure 5: Performance comparison based on the number of activated ports.