Joint Relay and Jammer Selection for Covert Communication

In this paper, we investigate covert communication where the relay and the jammer are jointly selected. It is demonstrated that the improvement of covert communication performance can be achieved under the proposed maximum-and-minimum-selection (MMS) scheme. Specifically, the relay with maximal channel gain to the legitimate destination (Bob) is selected to forward the covert signal when the jammer with minimal channel gain to Bob sends artificial noise to confuse the warden (Willie). We derive the expressions of detection error probability and effective covert rate in closed-form. Based on the derivations, the transmit power of relay is optimized to further improve the covert communication performance. The simulation shows that the effective covert rate cannot always be improved by increasing the number of relay, and there exists an optimal jamming power to maximize the effective covert rate.