Research On Relay Selection Algorithm Of Cooperative NOMA Communication Network

In recent years,with the rapid development of the 5th Generation mobile communication technology,a large number of devices have access to the network,and the wireless spectrum resources are increasingly scarce.The spectrum resources can no longer meet the access requirements of a large number of devices.In addition,the coverage of communication base station is limited,and the access of mass equipment also causes the problem of poor communication quality for users at the edge of base station.The cooperative non-orthogonal multiple access communication network enables different users to use the same time domain and frequency domain resources,solves the problem of spectrum resource shortage,and uses the cooperative communication mode of relay to break through the limitation of base station coverage,and improves the communication quality of edge users.In order to improve the transmission performance of the cooperative non-orthogonal multiple access communication network,this thesis studies the relay selection algorithm of cooperative non-orthogonal multiple access communication network.The specific research contents are as follows:Firstly,aiming at the problem that the relay selected by the relay selection algorithm based on quality of service cannot guarantee the target rate of the user with high quality of service priority at the destination node,which results in poor system outage performance,an improved DRS-FPA relay selection algorithm is proposed.The improved algorithm gives priority to the user with high quality of service priority in the second stage.On this basis,a dual relay set that can meet the target rate of the transmission user is constructed,and two relays are selected based on the maximization criterion.Simulation results show that the improved DRS-FPA relay selection algorithm improves the outage performance of the system compared with the unimproved algorithm.Secondly,in view of the fixed power allocation relay selection algorithm can not adapt to channel conditions,cause waste of resources,power system outage problem of poor performance,an improved full dynamic power allocation of relay selection algorithm,algorithm considering user’s quality of service priority according to the current link channel conditions is introduced into the dynamic power factor,can adaptive to adjust power users,The algorithm has the ability to adjust channel conditions.The algorithm makes full use of the system power to improve the user rate,and finally reduces the system outage probability.The simulation results show that the relay selection algorithm with improved full dynamic power allocation satisfies the target rate of users with high quality of service priority,the rate of users with low quality of service priority is significantly improved,and the system outage probability is significantly reduced.Finally,in order to further expand system coverage and improve system applicability,simultaneous wireless information and power transfer is introduced into cooperative NOMA communication network.However,power segmentation factor causes system energy limitation,resulting in system outage performance decline.To solve this problem,SWIPT-FDPA relay selection algorithm is proposed.In this algorithm,the current link channel condition,transmission power and power segmentation factor are included into the relay selection judgment conditions,and the system power is allocated reasonably to reduce the adverse impact of power segmentation factor on the system.Aiming at the problem that the maximum and minimum criteria based on channel gain are not equivalent to the maximum and minimum criteria based on user rate,an improved SWIPT-FDPA relay selection algorithm is proposed,which improves the user rate again.Furthermore,considering the influence of incomplete channel estimation on the performance of actual communication process,the existence of channel estimation error makes the relay selection algorithm of traditional dynamic power allocation appear power allocation error,resulting in the complete outage of system communication.To solve this problem,an incomplete CSI-SWIPT-FDPA relay selection algorithm is proposed.The channel estimation error is considered in power distribution.Simulation results show that although incomplete CSI-SWIPT-FDPA relay selection algorithm can not completely eliminate the influence of channel estimation error on system performance,it can significantly reduce the problem of high outage probability and low user rate caused by channel estimation error,and effectively improve system performance.