A Study Of Relay Selection For Cooperative NOMA Network

As one of the 5G candidate technologies,non-orthogonal multiple access(NOMA)technology based on power domain can serve multiple users at the same time.NOMA allows all users share time-frequency resources,improve spectrum efficiency and user fairness.Collaborative relay technology can obtain spatial diversity gain,effectively improves the wireless transmission throughput,reliability and coverage and other performance.The combination of NOMA and collaborative relay technology play a role in serving multiple users in the same frequency and enhancing the reliability of the networks.In the multi-relay NOMA cooperative system,different relay selection scheme will affect the signal-to-noise ratio of the receiver,thus affecting the system's outage performance.Therefore,in the multi-relay NOMA cooperative system,it is necessary to design a suitable relay cooperation scheme to improve the signal-to-noise ratio of the receiver and reduce the outage probability.NOMA is based on power domain multiplexing technology,the receiver adopts the successive interference cancellation(SIC)technology to decode the superposed signal,so the power allocation factor division at the transmitter will directly affect the decoding quality at the receiver.Aiming at the above problem,this paper designs optimal relay selection transmission criterion to improve the outage performance in NOMA cooperative network without direct link,and achieves low complexity distributed relay selection through node information interaction under the transmission criterion.Then,the convex programming and exhaustive search algorithm is designed aiming at the minimization of the outage probability to allocate the power factor of the source node and the relay node.Furthermore,based on the NOMA collaboration technology,the networks of base station by means of multiple simultaneous wireless information and power transfer(SWIPT)relay communicate with two users is studied,taking into account the situation that the communication has to be interrupted due to the limited energy of the relay node,consider the direct link,the edge user of the cell has a higher priority,the user in the center of the cell has a lower priority.According to the transmission quality of the edge user,a relay selection transmission strategy based on SNR is designed.The strategy consists of two phases: the first stage,establish a relay set which can correctly decode the two users;the second stage,if the firststage of the edge user can correctly decode,select the relay of the largest product of the remaining energy and the link gain to the center user to assist the central user transmission;if the edge user fails to correctly decode,select the relay of the largest product of the residual energy and the link gain to the edge user to assist the two users.The simulation and analysis results show that the proposed relay transmission strategy can improve the performance of the users by acquiring the diversity gain,simultaneously improve the spectrum utilization efficiency and energy efficiency.