On The Physical Layer Security Performance Of Mixed RF-FSO Systems With Interference

The accelerated growth in demand for wireless communication equipment has brought increasing attention to the issue of spectrum scarcity.Compared with Radio Frequency(RF),Free-space optical(FSO)is highly directional and secure,and has the advantages of free licensing,lower cost and higher bandwidth.However,it is easily affected by bad weather,such as snow,fog,haze,etc.,and is not suitable for long-distance communication.A mixed RF-FSO system can effectively overcome the above problems,allowing RF and FSO to play complementary roles.Considering the broadcast nature of RF channels in hybrid systems,the security performance of the system is at risk in the presence of malicious eavesdroppers.Therefore,ensuring the secure transmission of confidential information becomes more and more important,and the physical layer security of mixed RF-FSO systems is beginning to receive widespread attention.In order to better simulate the actual fading environment and improve the physical layer security of the system,this paper makes the following research on the physical layer security of the RF-FSO system:Firstly,a mixed RF-FSO system with wireless energy charging jammer based on time protocol is proposed,and the physical layer security performance of the system is studied.Independent jammers are set near the RF link,and energy transfer and collection techniques and time-switching protocols are introduced on the jammers to make the jammers more controllable and stable while achieving wireless energy charging.The closed and asymptotic approximation expressions for the Secrecy Outage Probability(SOP)and Average Secrecy Capacity(ASC)of the RF-FSO system are derived,and the Monte Carlo(MC)method is used to verify the expressions The correctness of the expressions is verified using the MC method.The physical layer security performance of the RF-FSO svstem with and without interferer is simulated.The effects of key factors such as average interference-tonoise ratio,number of interfering antennas,energy conversion efficiency,time allocation factor and receive aperture size on the system secrecy performance are also investigated.The results show that increasing the average interference noise ratio and the number of antennas of the jammer,adjusting the time allocation factor and applying the aperture technique can effectively improve the physical layer security performance of the system.Second,an RF-FSO system with RF links considering κ-μ distribution and cochannel interference is proposed,and the physical layer security performance of the system is investigated.A more generalized mixed fading model is considered,where the RF link and the FSO link follow the κ-μ distributed and Exponentiated Weibull(EW)distributions,respectively.In addition,the impact of co-channel interference on the physical layer security performance is considered,and Multiple-Input MultipleOutput(MIMO)techniques are used to counteract the interference impact.The SOP of the RF-FSO system is derived and the correctness of the expression is verified using the MC method.The SOPs are compared and analyzed with and without the effect of co-channel interference.The effects of co-channel interference intensity,the number of antennas at the transmitter and relay receiver,κ-μ fading parameters,receive aperture size,and the number of eavesdroppers on the physical layer security performance of the system are investigated.The results show that the physical layer security of the system is significantly reduced by the effect of co-channel interference,and the negative effect of co-channel interference can be effectively overcome by adjusting the κ-μ fading parameters and applying MIMO and aperture techniques to improve the physical layer security of the system.The research in this paper provides a good theoretical basis for the physical layer security performance of the mixed RFFSO system.