On The Performance Of Nth Best Relay Selection Scheme For NOMA-based Cooperative Networks

The tremendous development of wireless communication technology has changed the way of life of human beings greatly.Meanwhile,the great change of the way of life of human beings has stimulated the development of wireless communication technology in return.However,how to improve the performance of communication networks under the condition of limited resources of spectrum and various natural energy is an important issue in the development of modern network technology.Non-orthogonal multiple access(NOMA)technology as an important alternative technology in the 5th generation wireless system(5G)and the simultaneous wireless information and power transfer(SWIPT)technology which attracted much attention recently due to energy shortages can improve spectrum and energy utilization greatly and it is the main trend for future communication technology development.Based on the cooperative communication network of NOMA system,this thesis studies the non-optimal relay selection scheme combining with SWIPT technology to improve the energy efficiency of the system.This thesis focus on the outage performance and diversity order of the proposed system model.Firstly,the basic knowledge and key technologies related to this research are briefly introduced and analyzed.This thesis briefly introduces the key technologies of non-orthogonal multiple access,multi-relay cooperative communication and simultaneous wireless information and power transfer technology,including the technology of successive interference cancellation,power allocation and receiver design.Secondly,the Nth best relay selection scheme is proposed on the basis of NOMA cooperative networks,and the system model is established with SWIPT and without SWIPT technology respectively.The research scope of this thesis is downlink scenario,which includes a base station,two users with different QoS and M relays.Each device of the model is equipped with a single antenna,and the channel is affected by Rayleigh fading and independent of each other.On the basis of the established model,the closed expressions and asymptotic expressions of outage probability are deduced by using relevant mathematical tools.At the same time,the diversity degree of the Nth best relay selection scheme in this system can be expressed as M-N+1,where M represents the number of all relays and N is the order number of the selection scheme.Finally,in order to verify the theoretical analysis results,the outage performance of the system is simulated by using Monte Carlo method in MATLAB.At the same time,according to the characteristics of simulation curves under different parameters,the influence of different parameters on the outage probabilit y of the system is analyzed.The effects of the total number of relays,sequence number of relay and power splitting ratio on the outage performance of the system proposed are revealed.In addition,the outage performance of the system with or without the introduction of SWIPT technology is compared,and the antagonistic relationship between system performance and system energy consumption is revealed.In this thesis,the Nth best relay selection scheme is introduced into NOMA system for the first time.The relay selection scheme in cooperative NOMA system focuses on the optimal relay selection in the existing literature.However,in practical scenarios,the optimal relay may not be selected because of some special reasons,such as the optimal relay has been occupied,the system scheduling and balance,etc.It is of great significance to study the Nth best relay selection scheme in NOMA system considering the practical engineering application.