Covert Communication in Two-way Relaying Systems

In this paper, we examine covert communication in two-way relaying networks. We consider a scenario that two legitimate users forward messages to each other via a relay, while the relay will opportunistically transmit its own message to a covert user. To prevent covert communication, a legitimate user assumes the role of a monitor to detect relay's covert transmission. Through theoretical analysis, we derive expressions for the probability of detection error (PDE) and average covert rate (ACR), facilitating a thorough examination of the impact of system parameters on covert performance. Findings indicate that utilizing low, fixed-rate transmission, coupled with pronounced large-scale fading in the legitimate channel, markedly improves communication covertness. However, an ACR gain can be obtained from low to high fixed-rate region, when the large-scale fading of the legitimate channel is low.