On the Physical Layer Security of Mixed FSO-RF SWIPT System With Non-Ideal Power Amplifier

Free-space optical (FSO) links are contemplated as a potential paradigm to yield efficient point-to-point communication in wireless systems. Notably, these links are used to provide the proficient wireless connectivity between the radio frequency (RF) wireless network and the fiber optic-based network. To this end, more attention has been paid to mixed FSO-RF systems where single-hop FSO transmission and single-hop RF transmission configuration is used. In this paper, we propose a mixed FSO-RF dual-hop simultaneous wireless information and power transfer (SWIPT) relaying system in the presence of power amplifier (PA). It is assumed that FSO links suffer from Málaga (M)-turbulence with pointing errors and RF links experience the double shadowed Rician fading. Particularly, the physical layer security is analyzed by deriving the closed-form expressions for secrecy metrics such as secure outage probability, strictly positive secrecy capacity, and secrecy throughput. We consider the three scenarios: 1) FSO-side eavesdropping attack 2) RF-side eavesdropping attack 3) Simultaneous FSO- and RF-side eavesdropping attacks. The asymptotic approximations for the final results are also derived to obtain secrecy diversity order. The effect of SWIPT parameters and PA efficiency on the secrecy performance are then further investigated in detail. In summary, the results show that the reliability and security of the proposed system can be enhanced by utilizing efficient PAs at the RF front end depending on the eavesdropper's location and can also be controlled by the SWIPT parameters.