Covert communication over multi-user channels
Arumugam, Keerthi Suria Kumar
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The objective of the proposed research is to characterize the maximum rate at which information can be transmitted reliably to a legitimate receiver over certain multi-user channels while simultaneously escaping detection from one or more adversaries. Specifically, we investigate the fundamental limits of covert communication over the following multi-user channel models — a K-user discrete memoryless multiple-access channel (MAC) monitored by a single warden, a discrete memoryless broadcast channel in which one of the receivers is a warden trying to detect the presence of a covert message, and a relay channel model in which the relay aids covert transmission amidst two non-colluding wardens each monitoring the transmitter and the relay, respectively. In all three models, we observe that the covert throughput is subject to the square-root law. Also, building upon a previous result that codeword-level asynchronism results in an improved covert throughput that circumvents the square-root law, we analyze the impact on the covert throughput as a result of symbol-level asynchronism at the receiver and the warden.