Problem
Research questions and friction points this paper is trying to address.
Covert Communications
Enormous Fluid Antenna Systems
Channel Hardening
Passive Warden
Detection
Covert Communications over Enormous Fluid Antenna Systems (E-FAS): Impact of Channel Hardening on Detection
🤖 AI Summary
This paper investigates the impact of channel hardening in extremely large fluid antenna systems (E-FAS) on the detection of covert communications by a passive warden. Based on a surface wave propagation model, the Bessel K distribution derived from random channel scales is analyzed to formulate the optimal likelihood ratio test and characterize the covert throughput. The study reveals an asymmetric effect of channel hardening: it enhances the reliability of the legitimate link while preserving channel fluctuations at the eavesdropper to improve covertness. Results demonstrate that under finite observations, the covert performance of E-FAS channels significantly surpasses the Rayleigh fading limit.
📝 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.
Innovation
Methods, ideas, or system contributions that make the work stand out.
Enormous Fluid Antenna Systems
Covert Communications
Channel Hardening
Bessel-K Distribution
Energy Detector
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