Enormous fluid antenna systems improve stealthy wireless communication detection
Covert Communications over Enormous Fluid Antenna Systems (E-FAS): Impact of Channel Hardening on Detection
Information Theory
Summary
Covert communication means sending messages without being noticed. This paper looks at how a special kind of antenna system called an enormous fluid antenna system (E-FAS) affects the ability to hide messages from someone trying to detect them. The antenna creates a channel with specific random properties, and the authors find that the best way to detect messages is by measuring signal energy. They show that certain properties of the channel can actually help keep communications stealthy under some conditions, even though the channel might improve communication quality for the sender.
What this means in practice
- •For wireless network engineers: Design wireless systems that improve hidden message sending by exploiting channel fluctuations in fluid antenna arrays.
- •For security system developers: Develop improved detection tools for covert signals that account for random channel variations in advanced antenna setups.
Authors
Farshad Rostami Ghadi, Damoon Shahbaztabar, Kai-Kit Wong, Wei-Ping Zhu
Abstract
Enormous fluid antenna systems (E-FAS) enable guided surface wave (SW) propagation and induce an end-to-end channel that is conditionally complex Gaussian with a random covariance scale. This paper investigates the impact of this channel structure on covert communication in the presence of a passive warden. Under an equal power effective mode representation, the random channel scale follows a Gamma distribution, leading to a Bessel-K distribution for the effective channel power. We show that the optimal likelihood ratio test at the warden reduces to an energy detector and derive the corresponding false alarm and missed detection probabilities. These results are then used to characterize the achievable covert throughput under a prescribed detection error constraint. Numerical results show that, for finite observation intervals, finite mode E-FAS channels improve covertness relative to the fully hardened Rayleigh limit with the same average channel power. They further reveal an asymmetric role of channel hardening: stronger hardening can improve the legitimate link, whereas retaining channel scale fluctuations at the warden can enhance finite observation covertness.