Physical Layer Security Performance Analysis For Multi-relay Multi-user NOMA Networks

Recently,with the vigorous development of modern information and communication,5G wireless communication technology is gradually popularized,and there is an increasing demand for information networks.Non-Orthogonal Multiple Access(NOMA)technology is one of the key technologies of 5G network,which can effectively improve spectrum efficiency.Through cooperative relay,NOMA system can further improve the reliability of information transmission.However,since wireless channels are broadcast and information is easy to be stolen,Physical Layer Security(PLS)is one of the important challenges faced by NOMA system.Therefore,it is very meaningful to study the physical layer security of cooperative NOMA system.In this paper,the physical layer security of multi-user cooperative NOMA system is deeply studied,and the following two tasks are completed.(1)For NOMA multi-relay system,considering the situation that signals sent by base station and relay can be eavesdropped,the security performance of the system.According to whether the eavesdropping channel status information is known,it is divided into PRS-CSI(partial relay selection strategy-channel state information),PRS(partial relay selection strategy)and full relay selection strategy(FRS),which assume that the eavesdropping link channel status information is known.The security performance of the three strategies is compared.The theoretical expressions of safe outage probability and safe throughput under each strategy are derived respectively.Finally,Monte Carlo simulation is used to verify the correctness of the analysis.The results show that the complete relay selection strategy(FRS)makes the security performance of the system optimal,but in reallife,the complete relay selection strategy is difficult to realize in terms of hardware requirements.The partial relay selection strategy known by eavesdropping channel is superior to the partial relay selection strategy unknown by eavesdropping channel,and the hardware implementation is not difficult,which can improve the security performance of the system.It has practical significance.(2)For the NOMA network model with multiple users and eavesdropping users,friendly jammers are introduced in the second time slot to interfere with eavesdropping users,and a joint scheme of relay selection and friendly jamming is used to enhance the system security performance.Theoretical expressions of safe outage probability and safe throughput under different relay selection strategies are derived.Finally,Monte Carlo simulation is used to verify the theoretical derivation and compare the influence of friendly jammer scheme on the system model.It is concluded that the safety performance of the system is improved when there are friendly jammers.