Performance Analysis and Optimization of FAS-ARIS Communications for 6G: System Modeling and Analytical Insights

TL;DR

This paper develops an analytical framework for FAS-ARIS in 6G, optimizing system parameters to enhance reliability and throughput, with validated simulations showing significant performance improvements over existing solutions.

Contribution

It introduces a unified analytical and optimization framework for FAS-ARIS in 6G, including novel gain and phase optimization methods under practical constraints.

Findings

Optimized ARIS amplification gain under power constraints.

Derived a tractable outage probability expression.

Achieved near-optimal throughput with low complexity algorithms.

Abstract

This paper introduces a unified analytical and optimization framework for fluid antenna system-active reconfigurable intelligent surface (FAS-ARIS) communications in 6G. By combining the port reconfigurability of FAS with the signal amplification of ARIS, the proposed design enables more flexible control of the propagation environment and enhanced link reliability beyond what passive solutions can offer. We first derive the optimal ARIS amplification gain under a reflection power constraint to maximize the user's signal-to-noise ratio (SNR). Using a block-diagonal matrix approximation, we obtain a tractable outage expression and a tight independent-antenna equivalent upper-bound. Building on this, we establish the monotonic relationship between outage and effective channel gain, which enables a closed-form solution for ARIS phase optimization under limited channel state information (CSI). To further improve spectral efficiency, we propose a region-partitioned throughput optimization framework that achieves near-optimal performance without exhaustive search, thereby verifying its low computational complexity. Extensive simulations confirm the accuracy of the analysis and demonstrate consistent gains in outage and throughput compared to baselines.