Research On Physical Layer Security Performance Of Cognitive Radio Networks

As one of the key technologies of cognitive radio networks(CRNs),dynamic spectrum access(DSA)technology can dynamically access idle authorized spectrum for cognitive transmission,so as to achieve the purpose of improving spectrum utilization.The open spectrum access environment of CRNs makes cognitive radio networks more vulnerable to security threats than traditional wireless networks.Therefore,this paper studies the secure transmission performance of cognitive radio networks from the perspective of secure transmission in physical layer.1)Firstly,based on orthogonal multiple access(OMA)technology,the physical layer security transmission performance of cognitive radio networks is studied.Considering the actual multiple eavesdroppers scenarios,a cognitive radio networks system model of multi-relay and multi-eavesdropper is established based on Nakagami-m fading channel.An optimized multi-eavesdropper cognitive relay transmission scheme is proposed,and the security outage probability of different relay selection schemes under different eavesdropping modes are deduced.The performance of different relay number,different eavesdroppers number and different channel fading are analyzed.Finally,the analysis results are verified by MATLAB.The results show that the proposed non-cooperative eavesdropping optimal relay selection scheme can obtain the lowest security outage probability.The physical layer security transmission performance can be improved by increasing the number of relays or reducing the number of eavesdroppers.2)Compared with OMA,non-orthogonal multiple access(NOMA)technology,as one of the key technologies of 5G,can better improve spectrum utilization and system throughput.In this paper,NOMA technology is applied to multi-cognitive user collaboration system,and a NOMA-based downlink cognitive user collaboration system model is proposed.The outage probability of primary user(PU)and secondary user(SU)of different cognitive users collaboration schemes under amplify and forward(AF)mode is analyzed.Compared with the outage probability of PU and SU in decode and forward(DF)mode.The results show that when the link condition of SU?PU is better,AF mode can improve the outage performance of PU,and the outage probability of PU can also be reduced by choosing the best cognitive user cooperation scheme.3)Space time block code(STBC)can effectively resist channel fading and improve transmission reliability by utilizing spatial multiplexing.This paper considers the application of STBC in the wireless cognitive NOMA system,and establishes a downlink cognitive NOMA system consisting of a base station and a pair of cognitive users with different fading conditions.The base station is equipped with two transmitting antennas,and the cognitive users are equipped with a single receiving antenna,and will be attacked by a single eavesdropper during transmission.Based on this model,the security outage probability of each cognitive user without considering channel sorting is deduced,and compared with the security outage probability of cognitive users in traditional wireless cognitive NOMA system.The research results show that the STBC-based wireless cognitive NOMA scheme proposed in this paper can better improve the physical layer security performance of cognitive users.