Research On User Power Distribution And Relay Selection In Cooperative NOMA Under Different Scenarios

With the rapid development of wireless communication technology,people have put forward higher requirements for the reliability and high efficiency of communication technology.As the core technology of next-generation mobile communication,NonOrthogonal Multiple Access(NOMA)has attracted the attention of scholars.NOMA can make access users to share time-frequency and space resources,which can improve the spectrum efficiency,and ensure the fairness among users by distributing power to access users.As an extension technology of multi-antenna technology,cooperative communication technology can share transmission path through mutual cooperative forwarding messages among single antenna devices to improve the received signal-to-noise ratio and the reliability.The combination of NOMA technology and cooperative communication has injected new vitality into wireless communication.In view of this,this paper studies the cooperative relay network based on NOMA.Firstly,this paper introduces the research background and significance of cooperative communication and NOMA,and introduces the propagation characteristics and diversity technology of wireless channels to a certain extent.On this basis,the working principle and development significance of collaborative NOMA are introduced,and the system capacities under NOMA and OMA is compared and analyzed.In the multi-relay cooperative NOMA system,different relay selection schemes will bring different signal-to-noise ratios to the receiving end,which will affect the system's outage performance.Therefore,how to design a reasonable relay cooperation scheme will directly affect the entire network outage performance.In this paper,two relay selection schemes using DF in a single-source multi-relay system are studied.Before the relay node forward the messages it needs to demodulate two kinds of information in the DF forwarding mode.Therefore the entire system does not occur outage need the relay node and the destination node satisfy the threshold rate.Two relay selection schemes were studied and compared.Further,a multi-user multi-relay cooperative NOMA network adapting AF forwarding is studied.Under the system model,a simple user-relay selection scheme based on instantaneous channel gain is proposed to study the system outage performance.The influence of power allocation factor on system outage performance is analyzed.In order to get the minimum system outage probability through the optimal power factor.According to the delay characteristics and QoS requirements of the destination node information,an adaptive power allocation factor is proposed.Based on this,the decoding constraints are found.Furthermore,the best "user-relay" selection scheme is proposed.And the outage performance is calculated and analyzed.Finally,the correctness of the analysis is verified by Matlab simulation.The results show that the user relay selection scheme proposed in this paper can effectively improve the system's outage performance by the adaptive power control,which enhance the reliability of the information transmitted by the system.