Research On The Physical Layer Security Technology Of Non-orthogonal Multiple Access

Recently,with the explosive growth of mobile data services and the massive access of smart mobile devices,current 4G communication systems have failed to meet the need of communication.The power domain non-orthogonal multiple access(NOMA)technology can improve spectrum efficiency and system capacity,and has become a research hotspot of the 5th generation mobile communication system.At the same time,the security challenges,which are brought by the access of a large number of devices in the network are equally severe,as a result,the research of NOMA technology has gradually developed into the field of physical layer security(PLS).The purpose of this paper is to promote the combination of the NOMA system and physical layer security research,and to provide assistance for designing a secure NOMA system.In this paper,the secrecy performance analysis of the downlink transmission scheme is carried out based on NOMA technology,then the theoretical analysis is verified by simulation.The achievement and contributions of this paper are summarized as follows:1.For the downlink multiinput single-output NOMA(MISO-NOMA)system,the research considers the existence of passive eavesdroppers in the system and performs secrecy performance analysis.Based on the research of the secrecy performance of the traditional MISO-NOMA system,this paper proposes a joint transmit antenna selection(TAS)and artificial noise(AN)signal aided transmission scheme.Unlike the traditional AN scheme,another antenna is used to transmit AN signal in the new scheme.In the proposed scheme,the total power is divided into a part of the AN signal,not only performing TAS at the base station,but also transmitting the AN signal together with the user information using superposition coding.And the solution method of the optimal AN signal distribution power coefficient is given and we derive the exact and asymptotic expressions of its secrecy outage probability(SOP).Under the same parameters,the simulation results show that the secrecy performance of the proposed scheme is significantly promoted.2.For the relay system of NOMA,in the case where all users and base stations have no direct link,the eavesdropper is considered to perform combined eavesdropping on the base station and the relay.Secrecy performance analysis was performed in the two scenarios of half-duplex relay(HD)system and full-duplex relay(FD)system.1)For the aforementioned full-duplex relay system,the eavesdropper can perform signal receive with using both selection combining(SC)and maximal ratio combining(MRC).When the base station is equipped with multiple antennas,the TAS technique is implemented,and the SOP closed-form expressions are derived.The simulation verifies the positive effect of the increasing number of antennas of the base station on the secrecy performance of the system,and it analyzes the impact of different combinations of eavesdroppers on system secrecy performance;2)Considering all communication nodes with single antenna,the model is extended to the NOMA full-duplex relay system,and there is loop self-interference at the full-duplex relay,and the closed-form expression of SOP is derived.Simulation results verify the correctness of theoretical analysis.The paper analyzes the difference which is between the secrecy performance of the NOMA full-duplex relay system and the NOMA half-duplex relay system.It is proved that reducing the self-interference of the full-duplex relay puts a positive impact on the secrecy performance of the system.Moreover,the paper also studied the impact of the power partition coefficient and the target transmission rate on the secrecy outage performance.