AI summaryⓘ
The authors created a new way to use very large, flexible antenna systems called Enormous Fluid Antenna Systems (E-FAS) to improve devices that both sense their surroundings and communicate at the same time. They built a detailed model showing how signals travel and bounce back in this setup, focusing on how well angles of targets can be estimated. Their findings show that E-FAS works differently from traditional antenna arrays and that simply boosting signal strength doesn't always improve sensing accuracy, highlighting a balance between signal routing and sensing variety. Tests confirmed that E-FAS could sense angles much better without increasing power, suggesting it could be a promising new method for combined sensing and communication systems.
Integrated Sensing and Communications (ISAC)Enormous Fluid Antenna System (E-FAS)Surface-wave routingFisher Information Matrix (FIM)Cramer-Rao Bound (CRB)Angular estimationReconfigurable electromagnetic apertureParametric observation modelSensing diversityProgrammable propagation environments
Authors
Farshad Rostami Ghadi, Kai-Kit Wong, Jose D. Vega-Sanchez, Kin-Fai Tong, Hyundong Shin
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.