Joint Secure and Covert Communication Study in Two-hop Relaying Systems

This paper investigates the joint secrecy and covert communication in a two-hop relaying system consisting of a transmitter Alice, a receiver Bob, an eavesdropper Eve and a Relay. Eve always overhears the secret message from Alice. Meanwhile, Alice transmits covert message on top of secret message without being detected by Relay. First, we propose a covert transmission scheme that Alice will transmit covert message only when the signal-to-interference-plus-noise-ratio (SINR) of the secret message is greater than a threshold. Then, we provide the closed-form expressions of covert performance, i.e., the optimal detection threshold of Relay and the corresponding minimal detection error probability as well as the average minimum detection error probability. Finally, extensive numerical results are presented to illustrate the impacts of the system parameters on covert performances. Remarkably, the corresponding theoretical results well match with the simulation ones indicating that our theoretical analysis can accurately model the covert performance of the considered system.