Research On Physical Layer Security Of OAM Multiplexing Communication Under Atmospheric Turbulence Channel

With the increasing scarcity of radio spectrum resources and the increasing demand for communication capacity,traditional RF domain communications have shown signs of fatigue in response to such rapidly growing traffic.In the context of rapid growth of data traffic,Free Space Optical(FSO)communication has become an alternative to data center a nd cell user information transmission with its advantages of large bandwidth,high capacity and easy deployment,and FSO chain.The road has also been rapidly developed and deployed in recent years.In an FSO link where there are two legitimate recipients,the eavesdropper can still perform eavesdropping by intercepting a portion of the transmitted beam energy on the laser transmission path,so the communication security of the FSO link is critical.This paper focuses on the physical layer security issues based on OAM multiplexing.Firstly,this paper studies the properties of several typical OAM beams,including Laguerre-Gaussian beams,hypergeometric beams and BesselGaussian light,and theoretically deduces and compares the mean square radius of several typical OAM beams..The best alternative beam for FSO multiplexed communication systems under finite aperture constraints is given.Secondly,the different power spectrum models of atmospheric turbulence are studied.The existing atmospheric turbulence phase-screen simulation algorithms are studied and compared,including the inverse method based on FFT algorithm and the compensation method of low-frequency component compensation.In this paper,the above two algorithms are implemented and compared,and the compensation method is used to generate the atmospheric turbulence phase screen with high precision.Then,a plurality of atmospheric turbulence screens are arranged in the FSO system and the transmission of the OAM beam under the atmospheric turbulence channel is simulated by the stepby-step propagation method.A large number of transmission experiments are carried out on the integer-order OAM multiplexing system and the arbitraryorder OAM multiplexing system.The effects of different turbulence intensi ties on the OAM beam are studied,and the interference of the mode transmission coefficients of each multiplexing system is given.Happening.Finally,the system capacity and physical layer security of the OAM multiplexing system are analyzed.The physical layer security of OAM multiplexing system under atmospheric turbulence channel is studied under the limitation of finite aperture.The equal power channel(Equal Channel Power,ECP)and fixed system power(FSP)power loss schemes are respectively compared and studied,and the performance of each OAM multiplexing system is given,and the integer order OAM multiplexing is performed.The performance of the system and the fractional OAM multiplexing system has been studied in depth.The simulation results show that the multiplexed fractional-order OAM beam can effectively improve the physical layer security of the multiplexed system under the finite aperture limitation.Finally,this paper studies the probability of forward secure communication of each system.