Non-orthogonal multiple Access(NOMA)technology is a promising multiple-access technology in the post-5G and 6G era due to its high spectral efficiency and massive connectivity.However,the broadcast nature of wireless systems poses serious challenges to reliable transmission of information.Physical layer security technology is based on information theory,which uses the uncertainty of wireless channel to improve the security performance of the system.In this paper,the physical layer security performance of NOMA system aided by Reconfigurable Intelligent Surface(RIS)was investigated.It can be divided into the performance analysis of classic Rayleigh fading channel and FisherSnedecor F composite fading channel.Firstly,the physical layer security performance of RIS-assisted NOMA system in Rayleigh fading channel is studied.In order to improve the system security performance in the case of single antenna eavesdropping on the user link from the transmitting end to the user,this paper builds the physical layer security system model of RIS cooperative NOMA communication,and deduces the safe Outage Probability.SOP,the exact solution of Strictly Positive Secrecy Capacity(SPSC)and asymptotic SOP under high SNR conditions.The results show that the use of RIS can improve the security performance of the system compared with the traditional NOMA system and the relay-assisted NOMA system.Secondly,the physical layer security performance of RIS-assisted NOMA system under compound fading channel is studied for the first time.The existing researches on physical layer security of NOMA system have all adopted Rayleigh and other multi-path fading models.In this paper,after summarizing common compound fading models,multi-path fading and shadow effect are considered simultaneously for the first time,and a single antenna illegal eavesdropping system model is built based on Fisher-Snedecor F compound fading channel model.The exact closedform analytical expressions of the interrupt probability and SOP and the asymptotic analytical expressions of SOP are derived.The results are verified by Monte Carlo simulation,and the influence of RIS reflection unit number,multipath fading parameters and shadow parameters on the system safety performance is analyzed.It makes up the gap in the research field of physical layer security of RIS-assisted NOMA system under the compound fading model. |