Performance Analysis and Optimization of Probabilistic Covert Transmission Assisted by Energy Harvesting

In this paper, a covert wireless-powered relay (CWPR) system with the aid of a full-duplex receiver is investigated, where the receiver acts as a friendly jammer to protect the subsequent communication activities from being detected, while transmitting radio frequency (RF) energy to charge the relay. Meanwhile, both the transmitter and the relay employ a probabilistic transmission strategy to initiate information transmission based on legitimate link information. In the multi-relay scenario, two relay scheduling schemes are proposed, namely, energy harvesting maximization scheduling (EHMS) scheme and first-hop link priority scheduling (FLPS) scheme. Then, we derive the minimum detection error probability (DEP) of the eavesdropper (Eve) in two phases, and conduct a thorough analysis of the covert performance of each scheme, including covert rate, covert energy efficiency (CEE) as well as covert outage probability (COP), and obtain the optimal transmission prior probability and the optimal jamming power under each scheme. The numerical results show that the proposed probabilistic transmission strategy can significantly enhance CEE compared to the conventional continuous transmission strategy. Moreover, the proposed transmission scheme is indeed effective in enhancing the covert performance, especially when there are significant differences in channel conditions between the two-hop links.