Multi-Antenna Covert Communication Achieved by Exploiting a Public Communication Link

A multi-antenna covert communication system under fading channels is proposed in this paper, where the existing public communication link is exploited as a cover. With the warden employing a radiometer for detection, we derive the closed-form expressions for warden's optimal detection threshold, as well as the minimal average covert probability used to characterize the covertness performance. Furthermore, an optimization problem for covert capacity is formulated to maximize the overall system performance. Also an optimal power allocation algorithm is proposed afterwards. Our simulation results illustrate that a win-win relationship between covert communication and public communication is achieved in the proposed system. Most of all, it is demonstrated that the covertness performance is invariant to noise level and warden's position, thus we can effectively defend the covert communication against a powerful warden adopting the power trend test (PTT) method.