Study Of Relay Selection For Cooperative NOMA Network

With the rapid development of wireless communication,people have higher and higher requirements for the performance of diversified communication scenarios.The communication system with characteristics of high efficiency,reliability and safety is the development goal of current and future wireless communication.As one of the new multi-access technologies for 5G,Non-orthogonal Multiple Access(NOMA)that uses power domain superposition can service multiple users at the same time and increase the frequency efficiency significantly.With the application of NOMA technology in collaborative communication,the effect of relay selection strategy on system interrupt performance has become one of the research hotspots.On the other hand,with the multiplication of access devices and the broadcast characteristics of wireless communication,the information security of communication network has attracted more and more attention from the society.The physical security technology can use the characteristics of wireless channel physical layer to protect the transmission security of communication,which can realize the integration of communication and security.This paper mainly focus on the relay selection strategy of NOMA cooperative network and the secure relay selection of NOMA cooperative network based on Simultaneous Wireless Information and Power Transfer(SWIPT)technology,then makes the following main work:(1)According to the NOMA cooperative network model,a passive relay selection strategy based on the interrupt probability of two users and the system is proposed,and a distributed relay selection criterion is designed.The exact expressions of the interrupt probability of two users and the whole system in the network are derived respectively and the approximate results of the interrupt probability and diversity gain are analyzed under high SNR.Then the effects of relay number,relay position and power distribution coefficient on the interrupt performance of two users are analyzed.Finally,the PRS strategy,Max-min relay selection strategy and two-stage relay selection strategy in NOMA cooperative network are compared to verify the effectiveness of the proposed strategy,and the Orthogonal Multiple Access(OMA)cooperative communication system is compared with the traditional selection strategy to verify the advantages of NOMA technology.(2)In view of the downlink communication scenario of edge users of the energyconstrained NOMA cooperative network under illegal eavesdropping,this paper proposes a optimal relay selection strategy based on the secure relay probability of edge users by using SWIPT technology to provide energy for the relay.The closed-form results of the outage probability for edge users and the approximate results for high signal-to-noise ratio(SNR)are derived under the optimal safety relay selection scheme.The effects of relay number,power segmentation factor,energy conversion efficiency and relay position on edge users' safety interrupt performance are analyzed.The simulation results show that the safety interrupt performance of edge users is greatly affected by the number and location of relays,but less affected by the power segmentation factor and energy conversion efficiency.The research of this paper shows that NOMA has a good application value in the application of cooperative network.