Energy efficiency analysis and enhancement for secure transmission in SWIPT systems exploiting full duplex techniques

Abstract

This paper investigates the secure transmission in simultaneous wireless information and power transfer (SWIPT) system, where a source node communicates with a wireless-powered full duplex destination node in the presence of a passive eavesdropping node. To take advantage of the benefits from SWIPT and full duplex techniques, we propose a two-phase time-sharing protocol: the destination node harvests energy form the source node in the first phase, while the information-bearing signal is transmitted under the protection of artificial noise sent from the destination node in the second phase. The transmit power of the artificial noise is converted from the harvested energy and self-interference exists at the destination. We derive the closed-form expressions for the connection outage probability (COP), the secrecy outage probability (SOP) and the transmission outage probability (TOP), based on which the secrecy energy efficiency (SEE) is formulated. Furthermore, we determine the optimal time allocation factor and transmission power that maximize the SEE while satisfying the COP and SOP constraints. Finally, numerical results verify our analytical results and show that there are tradeoffs among security, reliability and energy efficiency. When the residual loopback interference is mitigated under some certain level, our proposed optimization scheme can significantly boost the SEE.