Wireless-Powered Secure Transmission with Full-Duplex Relay and Imperfect Eavesdropper CSI

This paper focuses on information security in an energy harvesting relay system, in which confidential signals are transmitted from a source node to its desired destination with the assistance of one full-duplex (FD) relay. To empower simultaneous wireless information and power transfer, the time-switching (TS) protocol is embraced and the energy-limited FD relay node is powered by energy signals emitted by the source node. With the obtained statistical eavesdropper channel state information (CSI), the ergodic secrecy rate and its approximate expression are derived. As the objective is maximizing the ergodic secrecy rate performance, source beamformers, TS coefficient and the power control factor at FD relay are jointly optimized. To tackle the framed non-convex problem, an alternative method is hence proposed, and closed-form solutions for beamformers, TS coefficient and power control factor are derived iteratively. Besides, the convergence of our proposed algorithm can be guaranteed and is also theoretically proved. Simulation results demonstrate that our iterative algorithm is effective and improves the system secrecy rate considerably.