Implementing Fluid Antennas in the Beamspace: Performance Evaluation and Codebook Design

TL;DR

This paper evaluates metasurface-based fluid antenna systems for multi-user communications, extending models to reconfigurable designs and demonstrating significant performance improvements through interference cancellation techniques.

Contribution

It introduces a comprehensive performance evaluation and a practical codebook design for metasurface-based FASs, highlighting their advantages over conceptual models.

Findings

Metasurface-based FASs outperform conceptual FASs with proper design.

Interference cancellation via projection improves performance in interference-dominated regimes.

Numerical results show significant gains regardless of propagation characteristics.

Abstract

Metasurface-based fluid antenna systems (FASs) have been recently proposed as an inexpensive, scalable and practical alternative implementation for the fluid-antenna concept. This work thoroughly evaluates the performance of metasurface-based FASs in the context of multi-user communications. We extend the state-of-the-art signal model of FASs to electronically-reconfigurable designs, explicitly including the antenna response in the equivalent channel and resulting correlation structure. A general codebook design procedure, accounting for practical aspects like reflections and radiation efficiency, is presented and used to design the different antenna configurations (regarded as FAS ports). Importantly, we show that, with proper design, metasurface-based FASs can significantly outperform conceptual ones. While state-of-the-art theoretical embodiments of FAS rely on spatial flexibility for constructive/destructive interference, metasurface-based FASs exploit interference cancellation through projection onto the interference null space. Numerical results show a remarkable improvement when the system is dominated by interference (i.e., the natural FASs operational regime), regardless of spatial propagation characteristics.