An Adaptive Secure Transmission Scheme for Wireless Powered Communication Networks

This paper investigates secure transmission in a wireless powered communication network (WPCN) with an energy harvesting (EH) source configured with multiple antennas. In the WPCN, the EH source harvests energy from the radio frequency (RF) signals broadcasted by a power beacon (PB), and purely relies on the harvested energy to communicate with the destination in the presence of passive eavesdroppers. It is noteworthy that the RF-EH source is equipped with a finite energy storage to accumulate the harvested energy. To enhance the security, we propose an energy-aware transmit antenna selection (EATAS) scheme. According to the energy status and the channel quality, the source adaptively decides to transmit confidential information or harvest RF energy. For evaluating the secrecy performance, we first study the evolution of the energy storage, and then derive the analytical expressions of connection outage probability (COP), secrecy outage probability (SOP) and effective secrecy throughput (EST). Numerical results demonstrate that our proposed scheme outperforms the existing accumulate-then-transmit (ATT) scheme.