On Secrecy Energy Efficiency of RF Energy Harvesting System

The increasing use of information source in unreliable wireless communication is a driving force to explore the networks' energy efficiency and security. To fully improve the performance of the system, in this paper, we combine these two directions and investigate the secrecy energy efficiency (SEE) of the network in which the information can be eavesdropped consisting of an energy source, an information source, a destination and an eavesdrop node, all of which are equipped with single antenna. The system model is based on ST (save-then-transmit) protocol. The information source node harvests energy from the received signal power to charge its battery, which is used to retransmit the received signal to the destination. Under the limited transmit power mode, we get the expression for SEE, which depends on energy absorption rate and time. Our analytical results reveal that the secrecy efficiency has a maximum. The optimal energy absorption rate was further calculated by Newton iterative algorithm. Then we propose optimal energy source selection method. Simulation results finally verify the accuracy and efficiency of our proposed algorithm for secrecy energy efficiency maximization.