On the Fundamental Scaling Laws of Fluid Antenna Systems

TL;DR

This paper establishes fundamental scaling laws for the symbol error rate of fluid antenna systems in correlated channels, providing insights into how spatial diversity and port density affect communication performance.

Contribution

It introduces a rigorous analytical framework and closed-form asymptotic expression for SER, revealing the impact of spatial correlation and guiding optimal system design.

Findings

SER improves with increased antenna movement space for diversity.

Increasing port density within a limited space offers diminishing returns.

The derived scaling laws apply broadly to various modulation schemes.

Abstract

Fluid antenna systems (FAS) offer a promising paradigm for enhancing wireless communication by exploiting spatial diversity, yet a rigorous analytical framework for their error probability has been notably absent. To this end, this paper addresses this critical gap by unveiling the \textbf{fundamental scaling laws} that govern the symbol error rate (SER) of FAS in realistic, spatially correlated channels. To establish these laws, we derive a tight, closed-form asymptotic expression for the SER applicable to a general class of modulation schemes. This result is pivotal as it establishes the fundamental scaling law governing the relationship between SER and the channel's spatial correlation structure. Based on this framework, we provide a complete characterization of the diversity and coding gains. The analysis culminates in a definitive design directive: SER can be fundamentally improved by expanding the antenna's movement space to increase diversity, while merely increasing port density within a constrained space yields diminishing returns.