Research On Relay Selection And Security Policy In Cooperative NOMA System

Internet technology and smart devices have achieved huge development in the 21^stcentury,so that there is a huge demand for technological innocation.There is a growing demand for data and information privay because the number of wireless terminals is growing rapidly,mobile services have higher requirements for speed,delay and other indicators and users are paying more attention to the privacy and confidentiality of personal information.Up to now,large numbers of studies have found that the cooperative Non-Orthogonal Multiple Access(NOMA)technology and the Physical Layer Security(PLS)technology can meet the massive high-speed,low-latency connection and secure communication needs of future mobile communication networks.This thesis takes cooperative Noma system as the research objective to analyze and study the user pairing,relay selection and security and confidentiality issues in different scenes of the system.The main work is as follows:Firstly,this thesis proposes a joint algorithm which is implemented in steps based on distance,channel conditions and candidate subsets for user pairing and relay selection based on outage probability.The primary user is selected by the relative distance criterion firstly,then the pairing is performed according to the channel conditions between the primary user and the repeater,and finally the optimal user pairing is performed based on the user rate requirement to optimise the system outage probability.Compared with the traditional orthogonal multiple access system,it is proved that the proposed algorithm has better outage performance,not only that,the appropriate adjustment of system parameters can obtain better performance by simulation.Then,to solve the problem of secure and confidential transmission in the cooperative NOMA system,this thesis proposes a scheme for secure and confidential transmission in the cooperative NOMA system based on relay selection,by selecting two relays for information transmission and introducing artificial noise in the signal sent by the base station,so that the illegal eavesdropping user with unknown location is always disturbed by the signal containing artificial noise,the signal-to-noise ratio during decoding is always lower than the target signal-to-noise ratio to realize secure and confidential transmission in wireless communication system.Compared with the traditional cooperative Noma system without any security measures,the proposed scheme has better secrecy outage probability by simulation,and has the potential to be improved.