Fundamental Limits of Localization with Fluid Antenna Systems: A Fisher Information Analysis

TL;DR

This paper analyzes the fundamental localization limits of fluid antenna systems using Fisher information, deriving bounds and proposing port-selection strategies to enhance positioning accuracy in wireless networks.

Contribution

It introduces a unified Fisher-information-theoretic model for FAS localization, deriving closed-form bounds and proposing optimal port-selection algorithms.

Findings

Port-selection schemes significantly improve localization accuracy.

Derived closed-form Fisher information and error bounds for FAS.

Numerical results confirm the potential of FAS for high-precision localization.

Abstract

In this letter, we investigate the fundamental limits of localization in fluid antenna systems (FAS) utilizing a Fisher-information-theoretic framework. We develop a unified model to quantify the localization information extractable from time-of-arrival (ToA) and angle-of-arrival (AoA) measurements, explicitly capturing the synthetic aperture effects induced by FAS. Closed-form expressions are derived for the equivalent Fisher information matrix (EFIM) and the corresponding positioning error bound (PEB) in both user-side and base-station (BS)-side FAS configurations. Also, we propose optimal port-selection strategies based on greedy algorithms and convex relaxation to maximize the information gain under a constrained number of activated ports. Numerical results demonstrate that the proposed port-selection schemes can substantially tighten the PEB compared with random activation, thereby confirming the strong potential of FAS to enable high-precision localization. These results offer analytical insights and practical design guidelines for FAS-aided positioning in future-generation wireless networks