This paper presents a study of the physical layer security performance of a mixed radio frequency-free space optical (RF-FSO) system with a wireless-powered friendly jammer. The RF links undergo the Nakagami-m fading, and the FSO link experiences the Exponentiated Weibull (EW) distribution. A twohop decode-and-forward (DF) relay is present in the system. A single-antenna eavesdropper located on the RF link attempts to eavesdrop on the channel transmission information. There is a nearby multi-antenna jammer that can be charged wirelessly, and a save-then-transmit (ST) protocol is introduced in the jammer. The closed expressions for the secrecy outage probability (SOP) and the average secrecy capacity (ASC) of the mixed RF-FSO system are derived, and the correctness of the expressions is verified using the Monte-Carlo method. The influence of various key factors on the secrecy performance of the system is analyzed by simulations. The results show that increasing the average interference noise ratio, the number of interferer antennas, the time block allocation factor, and the size of the receiving aperture has a significant effect on the secrecy performance. This study provides a new system structure and a good theoretical basis for evaluating the physical layer security performance of mixed RF-FSO systems.Index Terms-RF/FSO, physical layer security, wireless powered jammer, save-then-transmit protocol I. INTRODUCTION he rapid development of wireless communication is leading to an accelerated growth in the demand for wireless communication equipment. Consequently, the problem of spectrum scarcity is getting more and more attention. Compared to radio frequency (RF), free-space optical (FSO) communication also known as the atmospheric optical communication [1] is highly directional and secure, free from interference caused by frequencies and adjacent bands, and has the advantages of free licenses, low cost and high bandwidth. However, it is susceptible to pointing errors and various environmental factors, and is not suitable for long-distance communication [2] [3].Mixed radio frequency-free space optical (RF-FSO) systems have been proposed in search of complementarity. The
This paper proposes a simultaneous wireless information and power transfer (SWIPT) energy-harvesting relay jamming based mixed RF/FSO system, and studies its security performance optimization in the presence of an eavesdropper. In this work, the RF and FSO channels experience Nakagami-m fading distribution and Málaga(M) turbulence, respectively. A two-hop decode-and-forward (DF) relay is presented in the system, and the effect of pointing errors is considered. The presence of a nearby single antenna eavesdropper that attempts to eavesdrop on the transmission is also modeled. In order to prevent eavesdropping, the relay introduces the SWIPT structure to control information delivery and wireless energy recharging. The closed expressions of secrecy outage probability (SOP) and average secrecy capacity (ASC) of the mixed RF/FSO system are derived for the above system model. In addition, the closed-form expression of the asymptotic results for SOP and ASC are derived when signal-to-noise ratios at relay and legitimate destinations tend to infinity. The correctness of these expressions is verified using the Monte Carlo method. The influence of various key factors on the safety performance of the system is analyzed by simulations. The results show that the safety performance of the system is considerably improved under good weather conditions as well as by increasing the signal-interference noise ratio, number of interferer antennas, power distribution factor and energy conversion efficiency. This study provides a new system structure and a good theoretical basis for evaluating the physical layer security performance of the mixed RF/FSO system.
This paper presents a new model, to the best of our knowledge, of a mixed underlay cognitive radio frequency (RF)/free space optical (FSO) system in which both RF and FSO links consider multiple-input multiple-output (MIMO) orthogonal space-time block coding (OSTBC). In a dual-hop decode-and-forward configuration, the underlay cognitive radio network RF and FSO links experience κ − μ and Γ − Γ fading, respectively. For the above system model, a closed expression for the outage probability of the mixed underlay cognitive RF/FSO system with MIMO-OSTBC is derived, and the simulation results are verified using the Monte Carlo method. The results show that considering MIMO-OSTBC in all links of the mixed underlay cognitive RF/FSO system can effectively improve the communication performance of the mixed system and alleviate the degradation in the communication quality caused by the atmospheric turbulence. The communication performance of the MIMO-OSTBC mixed underlay cognitive RF/FSO system is further improved by changing the key parameters, such as peak transmit power, fading parameters, the number of secondary user transmit antennas and relay receive antennas, and relative speed of the primary user.
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