Performance Analysis On Physical Layer Security Of Cooperative NOMA Systems

The fifth generation communication system(5G)raises a higher demand for wireless communication system by its ultra-high data rate,low latency,low power consumption and ultra-high connectivity.To cope with the explosive rising of mobile data in the 5G era,non-orthogonal multiple access(NOMA)has shown significant priorities over traditional orthogonal multiple access for its higher band efficiency,higher user fairness and large capacity domain,thus becomes a promising multiple access technique in 5G.Cooperative NOMA communication system provides extra diversity order,thus further enhances the system performance.Physical layer security(PLS)realizes secure communication utilizing the time variation properties of the wireless channel based on the information theory without any key.Cooperative NOMA and PLS have quickly become a hotspot for 5G communication research.This thesis can be summarized as follows:1.Modeling and analysis for the security performance in a cooperative NOMA system with multiple relays.Firstly the PLS of a cooperative NOMA system over the Rayleigh fading channel is studied.An optimal single relay selection scheme is proposed and the traditional multiple relay forwarding scheme is regarded as a benchmark.The different secrecy qualities of services of the two users and the dependence of their secrecy capacities are taken into consideration.The analytical expressions for the exact and asymptotic secrecy outage probability(SOP)of the cooperative NOMA system of two different schemes are derived.The results show that the secrecy diversity orders(SDO)of all the relay selection(RS)schemes under a fixed power allocation scheme are zero.2.The secrecy performance of the cooperative NOMA system over the Nakagami-m fading channel is further investigated and two new RS schemes,namely the two step relay selection(TSRS)scheme and the optimal dual relay selection(ODRS)scheme,are proposed.The analytical expressions for the exact and asymptotic SOP of different RS schemes are obtained.Moreover,the SDO and secrecy array gain of the cooperative NOMA system under different schemes are obtained.The Monte-Carlo simulation results are presented to validate our analysis and the impact of multiple parameters on the system performance are further investigated.Based on the modeling and analysis of the PLS performance of the cooperative NOMA system,this thesis proposes three RS schemes and compares them with traditional multiple relay forwarding strategy,investigates the impact of multiple different parameters on the security performance and analyzes the SOP under the high SNR scenario,thus provides the necessary theoretical references for the design and networking of the downlink cooperative NOMA system.