Research On Non-orthogonal Multiple Access Technology Based On Relay Selection In Cognitive Wireless Networks

The widespread use of cognitive radio technology can effectively alleviate the plight of spectrum shortage.Therefore,it's widely used in wireless networks.In this paper,relay cooperative transmission technology is combined with non-orthogonal multiple access(NOMA)technology.The joint technology has the advantages of expanding the coverage area of wireless communication,improving the system capacity and frequency band utilization rate.In cognitive wireless networks NOMA technology based on relay selection can significantly improve the spectrum utilization of authorized frequency band and the channel capacity of cognitive system under the condition of without affecting the normal transmission of primary users.This paper studies multi-relay cooperative transmission technology and NOMA technology in wireless communication networks from the perspectives of outage probability and channel capacity.The following research results have been achieved:Firstly,the concept of the best relay location is proposed,and obtains the binary coordinates of the best relay location by theoretical analysis.In addition,the influence of transmission distance between secondary source user and destination user on channel capacity is discussed.Theoretical analysis and simulation results show that,under the same transmission conditions,the best transmission mode can be selected by comparing the channel capacity obtained by three cooperative transmission models,thus maximizing the channel capacity.Secondary,an underlay mode downlink system based on NOMA is proposed in the case of without affecting the normal transmission of primary users.We consider two cases:(1)the NOMA transmission is carried out by the interference-oblivious secondary user.Such situation happens when the primary user starts its transmission after the CSI acquisition and feedback stage of cognitive users;(2)the secondary user is aware of the primary user interference and adapts the NOMA transmission according to the actual SINR.This case corresponds to a steady primary user which keeps its transmission during both stages of SU CSI acquisition and secondary user communication.We conduct analysis for both cases and derive the analytic expressions for outage probability.The analysis shows that NOMA transmission with interference-oblivious secondary user yields a performance loss compared with that with interference-aware secondary user.Finally,considering the above two points,under the premise of chapters 3 and 4,this paper proposes a relay-based NOMA downlink communication system model.According to the concept of relay optimal location proposed in chapter 3,two relay selection algorithms based on optimal location and relay selection algorithm based on link maximum channel capacity are proposed.The theoretical analysis is verified by simulation.