Rethinking Hardware Impairments in Multi-User Systems: Can FAS Make a Difference?

TL;DR

This paper explores how fluid antenna systems (FAS) can improve multi-user communication performance and robustness, especially in the presence of hardware impairments, through joint optimization of antenna positions and beamforming.

Contribution

It introduces a novel joint optimization framework for FAS in multi-user systems with hardware impairments, employing advanced algorithms to maximize minimum user rates.

Findings

FAS significantly improves system performance and robustness.

Deploying FAS at the BS alone offers substantial gains even with low power.

Space constraints can limit FAS benefits compared to fixed antennas.

Abstract

In this paper, we analyze the role of fluid antenna systems (FAS) in multi-user systems with hardware impairments (HIs). Specifically, we investigate a scenario where a base station (BS) equipped with multiple fluid antennas communicates with multiple users (CUs), each equipped with a single fluid antenna. Our objective is to maximize the minimum communication rate among all users by jointly optimizing the BS's transmit beamforming, the positions of its transmit fluid antennas, and the positions of the CUs' receive fluid antennas. To address this non-convex problem, we propose a block coordinate descent (BCD) algorithm integrating semidefinite relaxation (SDR), rank-one constraint relaxation (SRCR), successive convex approximation (SCA), and majorization-minimization (MM). Simulation results demonstrate that FAS significantly enhances system performance and robustness, with notable gains when both the BS and CUs are equipped with fluid antennas. Even under low transmit power conditions, deploying FAS at the BS alone yields substantial performance gains. However, the effectiveness of FAS depends on the availability of sufficient movement space, as space constraints may limit its benefits compared to fixed antenna strategies. Our findings highlight the potential of FAS to mitigate HIs and enhance multi-user system performance, while emphasizing the need for practical deployment considerations.