Covert communication assisted by multiple friendly users with channel uncertainty

Abstract

Covert communication can hide the wireless transmissions of legitimate users from adversarial parties while guaranteeing a certain level of decoding performance at the receiver. In this thesis, we study a covert wireless communication system assisted by multiple friendly users under channel uncertainty. We consider the uplink communication channels, in which friendly users can generate interference to cover the transmission between legitimate parties. By adopting an opportunistic selection scheme, we create a high-interference transmission environment that the adversary is much more affected than the legitimate receiver. This work considers the worst-case scenario of covert communication where the adversary can employ the optimal approach

therein, the optimal threshold for the energy detector, which minimizes the average total detection error probability, is calculated in the closed-form. We then provide the optimal target rate and the optimal selection parameter by designing a joint optimization problem to maximize the covert throughput at the receiver. Finally, our theoretical results are analyzed and verified by comparing them with numerical search simulations. In addition, we conclude that to satisfy a certain level of covertness, there requires a minimum number of friendly users. The results of this work show a significant improvement in covert communication's efficiency, compared to the traditional three-node models.