Performance Analysis of the Two-Way Relay System with Covert Communication

Covert communication has emerged as a new transmission technology aiming at the privacy and security challenges in wireless networks. This paper considers the covert performance in a two-way relay-assisted network. Specifically, the source transmits public information to the legitimate user as a cover with the assistance of the two-way relay, and the uplink user secretly sends covert data to the source through the relay to prevent detection by the warden. To optimize the system design, we utilize the physical layer network coding (PNC) technology to encrypt covert data, which can achieve absolute security in the relay forwarding stage. Then, the detection error probability (DEP) and the optimal detection threshold that determines the performance limit of the warden detector are derived under the covertness constraint. In addition, we investigate the physical layer security (PLS) performance of the considered network. In the case of the warden as the eavesdropper, we propose a new performance metric-covert intercept probability (CIP) and jointly analyze the security and reliability of data transmission with the system outage probability (OP). Finally, the approximate results under high signal-to-noise ratio (SNR) and the impact of relevant parameters are studied in detail. The Monte Carlo simulation results verify the accuracy of theoretical derivation and the effectiveness of two-way relay-assisted covert communication.