Research On Physical Layer Security Of The Mixed RF/FSO System

Compared with traditional radio frequency(RF)communication,Free Space Optical Communication(FSO)not only has high broadband capacity and unlicensed spectrum,but also has extremely high data transmission rate.However,the FSO system is susceptible to unfavorable factors such as pointing error and atmospheric turbulence,which makes it unsuitable for long-distance communication.The mixed RF/FSO system expands the communication range and complements the advantages of the two communication systems to improve the communication quality of the system.However,due to the openness and broadcast nature of wireless communication,there is a risk of information transmission being leaked.In order to cope with this risk,researchers have proposed Physical Layer Security(PLS)to improve the security of communication systems.This study discusses the general performance and PLS performance of the mixed RF/FSO system in different scenarios,and uses spatial diversity techniques and aperture averaging technology to enhance the physical security performance of the system.The main research contents of this paper are as follows:Firstly,the general performance of the mixed RF/FSO system is studied.It is assumed that the RF link and the FSO link experience Nakagami-m distribution and Fisher-Snedecor(37)-distribution fading,respectively.The cumulative distribution function(CDF)of the end-to-end signal-to-noise ratio(SNR)for the whole system under the DF and AF strategies is derived.Furthermore,the closed-form expressions of three indicators describing the system performance are obtained: Outage Probability(OP),Average Bit Error Rate(ABER)and Ergodic Capacity(EC).Finally,the performance of the system is analyzed by simulation.Secondly,the physical layer security(PLS)performance of the mixed RF/FSO system is studied,the cumulative distribution function of the end-to-end signal-to-noise ratio for the whole system under the decode-and-forward relaying protocol is derived.Furthermore,the closed-form expressions of three indicators describing the security performance are obtained: Secrecy Outage Probability(SOP),Average Secrecy Capacity(ASC)and Strictly Positive Secrecy Capacity(SPSC).Finally,the physical security of the mixed system is analyzed by simulation.Finally,in order to improve the physical security of the system,the spatial diversity techniques and aperture averaging technology are applied to the mixed RF/FSO system,and the PLS performance of the mixed SIMO-RF/FSO system is studied.The closed-form expressions of SOP and ASC for DF and AF system are derived by using the Maximal Ratio Combining(MRC)scheme.The effects of spatial diversity techniques and aperture averaging technology are analyzed by simulation.