Covert Blockwise Coding with Sequential Detection over Thermal-Loss Bosonic Channels

2026-06-17

AI Summary

This work addresses receiver-oriented covert communication over thermal-loss bosonic channels by proposing a block-wise binary supersymbol sequential detection framework. By characterizing the asymmetry in information growth rates—linear for the legitimate receiver Bob versus quadratic for the warden Willie—under the low-signal regime, the authors design a uniform signaling strategy that satisfies a per-block covertness budget and integrates a CUSUM detector to enable high-probability rapid detection within a single block. The study establishes, for the first time, a physically realizable block-sequential covert communication architecture, derives the minimum detection segment length required to guarantee exponentially decaying detection error probabilities, and formulates finite-horizon codebook design criteria for covert communication. These results provide a theoretical foundation for practical quantum covert optical communication systems.

Abstract

We develop, to our knowledge, the first receiver-centric blockwise sequential-detection framework for covert communication over thermal-loss bosonic channels. In this architecture, each block serves as a binary super-symbol, and the key design problem is to determine the minimum detection-segment length that enables Bob to detect an active block before the block ends while remaining covert to Willie. For any fixed physically realizable general-dyne receiver, Bob's post-change information growth is linear in the small-signal regime, whereas Willie's detectability obeys a quadratic quantum relative entropy law. Exploiting this asymmetry, we show that under a per-block covertness budget the asymptotically optimal signaling strategy is uniform across the detection segment, and we derive an explicit minimum-length condition under which a single-pass cumulative sum (CUSUM) detector crosses threshold within the same block with exponentially high probability. The resulting design law yields a covert blockwise binary codebook over a finite transmission horizon and establishes a concrete link between bosonic covert communication, sequential detection, and blockwise signaling design. More broadly, these results provide design guidance for covert quantum communication systems with physically realizable receivers, and help bridge information-theoretic covertness guarantees with implementable receiver-aware optical communication design.

Problem

• covert communication
• thermal-loss bosonic channels
• sequential detection
• blockwise signaling
• quantum covertness

Innovation

• covert communication
• sequential detection
• bosonic channels
• CUSUM detector
• quantum relative entropy