Optimizing Fluid Antenna Configurations for Constructive Interference Precoding

TL;DR

This paper proposes a novel optimization method for fluid antenna systems to minimize symbol error probability in multiuser MIMO, demonstrating improved performance and low computational complexity over existing approaches.

Contribution

It introduces a new joint SEP minimization framework for FAS with constructive interference precoding, transforming it into a safety margin maximization problem and solving efficiently.

Findings

Reduces bit error rate compared to fixed arrays and PSO-designed FAS.

Achieves lower computational complexity than PSO benchmarks.

Demonstrates effectiveness through simulation results.

Abstract

The fluid antenna system (FAS) has emerged as a new physical-layer concept to provide enhanced propagation conditions for multiuser multiple-input multiple-output (MIMO) communications over conventional fixed arrays. This work focuses on minimizing the maximum symbol error probability (SEP) under $M$-ary phase shift keying (MPSK) signaling in a multiuser downlink equipped with FAS, where each antenna moves within nonoverlapping intervals. This specific problem of joint SEP minimization with FAS and constructive interference (CI) precoding has not been previously addressed. The resulting problem turns out to be a nonconvex and nonsmooth optimization challenge. We transform the SEP minimization problem into a safety margin maximization problem in constructive interference precoding. Then, we customize a smoothing technique and a block coordinate descent (BCD) algorithm, with emphasis on low computational complexity. Simulation results show that our approach can reduce bit error rate (BER) compared to both the fixed arrays and FAS designed by existing particle swarm optimization (PSO). Also, our approach shows attractively low computational complexity compared to PSO benchmarks.