Structural Limits of Soft Fusion in Multi-Warden Covert Communication

A new paper on arXiv (2604.22790) by Abbas Arghavani, Subhrakanti Dey, and Anders Ahlen investigates the structural limits of soft fusion in multi-warden covert wireless communication. The study focuses on a Fusion Center (FC) that aggregates raw energy measurements from multiple Wardens to detect covert transmissions. The researchers extend prior work on power-threshold randomization by considering a stronger adversarial model where FC randomizes both the number of active Wardens (W) and the detection threshold (t), while Alice and a friendly Jammer jointly randomize their transmit powers under an outage constraint at Bob.

The key finding is a closed-form expression for FC's optimal soft-fusion threshold, which is shown to be independent of the number of active Wardens. This means that strategic uncertainty in the sensing infrastructure provides no meaningful detection advantage for FC under soft fusion. The paper establishes a robustness theorem showing that even under arbitrary FC randomization over (W,t), Alice and Jammer can maintain outage-feasible communication at Bob while preserving covertness with high probability, provided their power ranges are sufficiently large. This reveals a fundamental structural limitation of soft fusion.

Analytical and numerical results demonstrate three key points: 1) soft fusion is largely insensitive to the number of Wardens; 2) even semi-strategic finite-support geometric randomization of W performs comparably to the full game-theoretic equilibrium; and 3) the covertness-reliability tradeoff remains nearly invariant across a wide range of FC deployment costs and strategy parameters. These findings exemplify a Red Queen effect, where FC incurs increasing operational costs for only marginal gains in detection performance, highlighting the need for alternative detection architectures beyond soft fusion.