Research On The Performance Of Non-Orthogonal Multiple Access Cooperative Systems

Nowadays,the spectrum resource is increasingly scarce,Non-Orthogonal Multiple Access(NOMA)is considered to be a promising candidate for 5G multiple access schemes due to its superior spectral efficiency,higher throughput,and lower transmission delay.Cooperative communication forms a virtual Multiple-Input Multiple-Output(MIMO)system through users sharing each other's antennas,which realizes the diversity gain,channel capacity and communication quality,so it has a very broad application prospect.This paper studies the cooperative NOMA model from multi-user and multi-relay perspectives in the downlink communication scenario.The outage performance,optimal relay selection strategy and related factors affecting outage performance are analyzed.The main work of the thesis is as follows:A model of multi-user NOMA cooperation system is established,and the selection criteria of paired users are proposed.Considering whether there is a direct link or not,the expressions of pairing user outage probability,asymptotic expression and diversity gain of the system under high signal-to-noise ratio(SNR)are studied.The consistency between the accurate outage probability and the approximate outage probability is verified by simulation,and the influence of channel quality and relay location on the outage performance are analyzed.Finally,the performance of NOMA networks with different cooperation protocols is compared.The results show that the outage performance of the system using decode and forward(DF)protocol is better than that using amplify and forward(AF)protocol.A multi-relay cooperative system model of NOMA is established.Firstly,the Partial Relay Selection(PRS)strategie and its outage performance are studied.Then,the Reactive Relay Selection(RRS)strategy based on the two user is proposed under the model,and the outage performance and the factors affecting outage performance of the system are studied.Subsequently,closed-form results of the exact outage performance under the strategy and the approximate results in high SNR of are derived in detail.At the same time,the diversity performance and the optimal power allocation factor are obtained using the approximate results.Finally,the effects of relay position,channel quality,relay number and power factor on outage probability of the system are analyzed by simulation.Simultaneously,compared RRS strategie with PRS strategie in the same parameters,the results show that the outage performance of RRS is better than PRS.The work of this paper can enrich the basic theory of NOMA cooperative network and provide theoretical reference and guidance for the application of NOMA.