| With the massive deployment of the fifth-generation mobile communication network,the number of devices connected to the wireless communication system has exploded,resulting in a very scarce spectrum resource.Cognitive non-orthogonal multiple access(CR-NOMA)systems can effectively improve spectrum utilization and have been recognized as one of the essential solutions to solve the problem of spectrum resource shortage in future wireless communication networks.However,due to the open environment of the wireless channel,the wireless communication system has easily eavesdropped,and the issue of secrecy communication in the wireless communication system has attracted extensive attention.Relevant studies have proved that multi-antenna technology and relay cooperative technology can effectively improve the secrecy performance of traditional wireless communication systems.However,the research of the CR-NOMA system using the above two technologies to improve the secrecy communication performance is still in its infancy,and many problems need to be solved urgently.This thesis studies the secrecy communication performance in the CR-NOMA system.The main content of the thesis is summarized as follows:First,a multi-antenna spectrum sharing CR-NOMA system is considered,which transmits data through Rayleigh fading channels and proposes two antenna transmission schemes,maximum channel capacity(MCC)and space-time transmission(ST).The exact closed expressions of the secondary user’s secrecy outage probability(SOP)of the MCC and ST schemes are derived,respectively.In order to further reveal the influence of system parameters on the secondary user’s secrecy communication performance,the secondary user’s asymptotic SOP performance is studied.The correctness of the theoretical analysis is verified through Monte Carlo simulation.The research results show that the secrecy communication performance of the multi-antenna system of the MCC and ST schemes is significantly better than that of the single-antenna system.At the same time,as the peak transmit power of the base station increases,the SOP of the short-distance secondary users of the MCC scheme will always be better than that of the ST scheme,and the SOP of the long-distance secondary users will be worse than that of the ST scheme.Secondly,based on the previous research results,the SOP performance of the three secondary user multi-antenna spectrum sharing CR-NOMA systems is further studied.The exact closed expressions of the secondary user SOP and the system average SOP expressions of the MCC and ST schemes are derived and analyzed for their asymptotic performance.At the same time,using the simulated annealing(SA)algorithm based on the external penalty function to find the optimal power distribution coefficient so that the average SOP performance of the system can reach the best.The correctness of the theoretical analysis is verified through Monte Carlo simulation.The research results show that there is a unique optimal power allocation coefficient after the base station transmit power is optimized by the SA algorithm.The system average SOP performance of the ST scheme is 41% higher than that of the fixed power allocation coefficient(0.6,0.3,0.1),and the MCC scheme is improved by 1%-6%.Finally,the secrecy communication performance of a relay cooperative CR-NOMA system is studied,which transmits data in decode-and-forward mode through a Nakagamim fading channel,and the secondary user’s connection outage probability(COP)and SOP are derived,respectively.Further analysis is conducted on the asymptotic COP and SOP performance of secondary users,and the relationship between the power allocation coefficient and COP and SOP is obtained.The correctness of the theoretical analysis is verified by Monte Carlo simulation.Simulation results show that the COP performance of the system in the Nakagami-m fading channel is obviously better than Rayleigh fading channel,and the SOP performance of the system in the Rayleigh fading channel is slightly better than Nakagami-m fading channel. |
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