PASS-Enabled Covert Communications With Distributed Cooperative Wardens

TL;DR

This paper analyzes PASS-enabled covert communication with distributed wardens, deriving detection probabilities and optimizing system parameters to maximize covert rate while maintaining covertness, using advanced mathematical frameworks and algorithms.

Contribution

It introduces a comprehensive analytical framework for PASS-enabled covert communication with multiple wardens, including closed-form detection probability expressions and a robust optimization algorithm.

Findings

Distributed wardens significantly affect covert communication detectability.

PASS radiation laws influence the covertness-rate tradeoff.

The proposed algorithm effectively optimizes power and positioning for covert communication.

Abstract

This paper investigates PASS-enabled downlink covert communication in the presence of distributed surveillance, where multiple wardens perform signal detection and fuse their local binary decisions via majority-voting rule. We consider a dual-waveguide architecture that simultaneously delivers covert information and randomized jamming to hide the transmission footprint, incorporating three representative PASS power-radiation laws-general, proportional, and equal. To characterize the system-level detectability, we derive closed-form expressions for local false-alarm and miss-detection probabilities. By leveraging a probability-generating-function (PGF) and elementary-symmetric-polynomial (ESP) framework, combined with a breakpoint-based partition of the threshold domain, we obtain explicit closed-form characterizations of the system-level detection error probability (DEP) under non-i.i.d. majority-voting fusion. Building on this analytical framework, we formulate a robust optimization problem to maximize the average covert rate subject to covertness constraint. To solve the resulting nonconvex design, we develop an MM-BCD-SCA algorithm that produces tractable alternating updates for power/radiation variables and PA positions via convex surrogates and inner approximations of the DEP value function. Numerical results validate the theoretical analysis and demonstrate the impact of cooperative monitoring and PASS radiation laws on the covertness-rate tradeoff.