Enormous Fluid Antenna Systems (E-FAS) for Wireless Sensing: Channel Modeling and Conditional Estimation Limits

2026-06-22

AI Summary

This work addresses the limited angular sensing performance of conventional arrays and reconfigurable surface-assisted integrated sensing and communication systems, which struggle to exploit the advantages of large-scale electromagnetic apertures. Focusing on the emerging Enormous Fluid Antenna System (E-FAS), the study develops a bidirectional sensing channel model encompassing surface wave routing, distributed reradiation, target scattering, and echo propagation, and establishes a parametric observation framework. The Fisher information matrix and corresponding Cramér–Rao bound for angle estimation are derived, revealing a fundamental trade-off between surface wave routing gain and sensing diversity in programmable environments. The results demonstrate that E-FAS significantly enhances angular estimation accuracy under identical transmit power, validating the efficacy of jointly optimizing propagation paths and sensing functionality, and thereby positioning E-FAS as a novel paradigm for integrated sensing and communications.

Abstract

In this paper, we develop a fundamental analytical framework for integrated sensing and communications (ISAC) enabled by the Enormous Fluid Antenna System (E-FAS), which transforms a collection of coordinated intelligent surfaces into a gigantic reconfigurable electromagnetic aperture, with particular emphasis on the limits of angular sensing.We begin by developing a bidirectional sensing channel model that explicitly captures the complete sensing process, including surface-wave (SW) routing, distributed reradiation, target scattering, and echo propagation. Based on this channel model, we formulate a parametric observation model for target sensing and derive the associated Fisher information matrix (FIM) and Cramer-Rao bound (CRB) for angular estimation. The analysis demonstrates that E-FAS gives rise to a fundamentally different sensing regime compared with conventional array-based and reconfigurable-surface-aided ISAC architectures. Our analysis uncovers that maximizing coherent routing gain does not necessarily maximize sensing performance, exposing a fundamental trade-off between SW routing gain and sensing diversity in programmable propagation environments. Numerical results validate the developed framework and demonstrate that E-FAS-enabled ISAC systems can achieve substantial angular sensing gains over conventional architectures under the same transmit-power budget. The results further underscore the importance of jointly optimizing propagation routing and sensing functionality, positioning E-FAS as a new paradigm for ISAC.

Problem

• Enormous Fluid Antenna System
• Integrated Sensing and Communications
• Channel Modeling
• Angular Estimation
• Sensing Limits

Innovation

• Enormous Fluid Antenna System
• Integrated Sensing and Communications
• Channel Modeling
• Cramer-Rao Bound
• Surface-Wave Routing