Outage Performance Investigation For Multi-user NOMA Cognitive Relay Networks

Non-orthogonal multiple access(NOMA)and cognitive radio(CR)have attracted extensive attention for their ability to improve system capacity and spectral efficiency.Combining NOMA with CR network is one of the research hotspots in wireless communication field.Existing studies on CR-NOMA network mainly focus on the scenario where a primary user(PU)and a secondary user(SU)reuse the same authorized frequency band.For the multi-user CR-NOMA network,there are still many problems to be further studied,including the theoretical performance of multiuser network.Therefore,aiming at CR-NOMA network,this paper considers underlay and overlay spectrum sharing modes,to study the system performance under the co-existence of multiple users,and theoretically reveals the influence rule of system parameters on user performance.The main work of this paper is as follows.(1)For the multi-user CR-NOMA network model based on the Underlay spectrum sharing mode,the close expression of the outage probability for the near and far users in the secondary network and the system throughput are derived,as well as the approximate expression of the outage probability when the signal-tonoise ratio tends to infinity.The results are verified by simulation,and the effects of different parameters on user outage performance and the system throughput are analyzed.The experimental results show that the optimal user selection strategy can improve the outage performance with the increase of the number of users.In addition,in this mode,the target rate must be less than the ratio of power distribution factors of near and far users,so that users can communicate normally,otherwise users will be interrupted.(2)Aiming at cognitive NOMA system with imperfect successive interference cancellation,the close expressions of outage probability and the system throughput of PU and SU are derived,and the asymptotic expressions of outage probability when the signal-to-noise ratio approaches infinity are derived.The correctness of theoretical analysis is verified by experimental simulation.Experimental results show that imperfect SIC affects the outage performance of multi-user CR-NOMA networks.In addition,system throughput can be maximized when the target rate is equal to the ratio of power allocation factors of primary and secondary user.