Optimizing Fluid Antenna Configurations for Constructive Interference Precoding

2025-07-15

AI Summary

This work addresses the joint optimization of fluid antenna systems (FAS) and constructive interference (CI)-based precoding for multiuser MIMO downlink, aiming to minimize the maximum symbol error probability (SEP), under the constraint that each antenna’s position is continuously adjustable within non-overlapping intervals. We propose, for the first time, a unified framework that co-designs FAS antenna placement and CI precoding, formulated as a safety-margin maximization problem. To tackle the resulting non-convex optimization efficiently, we develop a low-complexity block coordinate descent algorithm leveraging smoothing techniques. Compared with conventional fixed-antenna arrays and PSO-based FAS designs, the proposed method achieves significant SEP reduction while substantially lowering computational complexity—thereby delivering both performance gains and practical feasibility.

Technology Category

• Search and Optimization: Mixed Discrete/Continuous Search
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Constraint Satisfaction and Optimization: Mixed Discrete/Continuous Optimization

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments
• Security and Privacy: Large-scale security measurements
• User Modeling, Personalization and Recommendation: Federated recommendation systems and personalization

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.

Problem

• Optimizing fluid antenna configurations for multiuser MIMO communications
• Minimizing symbol error probability in MPSK downlink with FAS
• Transforming SEP minimization into safety margin maximization problem

Innovation

• Fluid antenna system for MIMO communications
• Safety margin maximization in CI precoding
• Low-complexity BCD algorithm for optimization