Information-theoretically covert communications under variational distance constraint: limits and algorithms
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Wang, Shi-Yuan
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Abstract
The objective of the dissertation is to bridge the gap between the theoretical study of covert communications and the practical design of provably covert systems. Covert communications require the legitimate parties to establish reliable transmission without being detected by malicious adversaries. Although the optimal number of covert information bits has been shown to grow in the square root of channel uses, such square-root law can be circumvented by exploring the information asymmetry between the legitimate parties and adversaries. The covert capacity depends on how the covertness is measured by mathematical metrics. In particular, we choose the variational distance as the metric, as it captures the operational meaning of adversaries' hypothesis tests. These two aspects constitute the motivating threads of the entire dissertation. In the first half of the dissertation, we investigate covert communications over classical channels, including multi-antenna systems, covert code design, and asynchronism. In the second half of the dissertation, we extend our investigation to thermal-noise bosonic channels and present a resource-efficient scheme to exhibit the benefits of quantum entanglement for covert communications. Lastly, inspired by the recent development of joint communication and sensing systems, we characterize the information-theoretic limit of joint communication and sensing with a covertness constraint.
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2024-07-27
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Dissertation