Secure Transmission with Covert Requirement in Untrusted Relaying Networks

In this paper, we investigate the problem of secure communication with covert requirement in untrusted relaying networks. Our considered system model contains one source, one destination, one untrusted relay, and one Willie. The untrusted relay tries to extract the information signal, while the goal of Willie is to detect the presence of the information signal transmitted by the source, in the current time slot. To overcome these two attacks, it is assumed that the destination and the source inject jamming signal to the network in phase I and phase II, respectively. Accordingly, the communication in our proposed system model is accomplished in two phases. In the first phase, when the source transmits its data to the untrusted relay, the destination broadcasts its jamming signal. In the second phase, when the relay retransmits the received signal, the source transmits a jamming signal with one of its antennas. For this system model, we suggest a novel power allocation strategy to maximize the instantaneous secrecy rate subject to satisfying the covert requirements in both of the phases. Since the proposed optimization problem is non-convex, the Successive Convex Approximation (SCA) method is used to change it to a convex optimization problem. Numerical curves are presented to reveal the impact of the untrusted relay's location an number of source antennas on the secrecy performance.