On the Secrecy Capacity of a Full-Duplex Wirelessly Powered Communication System in the Presence of a Passive Eavesdropper
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In this paper, we investigate the secrecy capacity of a point-to-point, full-duplex (FD) wirelesly powered communication system in the presence of a passive eavesdropper. The considered system is comprised of an energy transmitter (ET), an energy harvesting user (EHU), and a passive eavesdropper (EVE). The ET transmits radio-frequency energy which is used for powering the EHU as well as for generating interference at EVE. The EHU uses the energy harvested from the ET to transmit confidential messages back to the ET. As a consequence of the FD mode of operation, both the EHU and the ET are affected by self-interference, which has contrasting effects at the two nodes. In particular, the self-interference impairs the decoding of the received message at the ET, whilst it serves as an additional energy source at the EHU. For this system model, we derive an upper and a lower bound on the secrecy capacity. For the lower bound, we propose a simple achievability scheme which offers rates close to the upper bound on the secrecy capacity. Our numerical results show significant improvements in terms of achievable rate when the proposed communication scheme is employed compared to its half-duplex counterparts, even for high self-interference values.
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