Research On NOMA For Relaying Systems

Recently,non-orthogonal multiple access(NOMA)has attracted much attention as a new5 G multiple access technology with high spectral efficiency.The main idea of NOMA is to linearly superimpose the information of multiple user which are in the same time domain,frequency domain and code domain through power domain multiplexing,and successive interference cancellation(SIC)principle is applied at the receivers to detected and separated the users' message step by step.In addition,in order to meet the growing communication requirements of people,cooperative relay systems have been extensively researched due to the advantages of improving the quality of wireless network communication,expanding network coverage and so on.Therefore,in the future 5G networks,the relay system based on NOMA will have broad application prospects.According to different NOMA relay system models,this paper will do a research combined with simultaneous wireless information and power transfer(SWIPT),energy harvesting(EH),multiple input multiple output(MIMO)and cognitive radio(CR)technologies.The system performance is studied by adopting antenna selection(AS),relay selection(RS)and joint relay and antenna selection(JRAS)schemes.The main research contents and contributions of this paper are as follows:1.Applying SWIPT technology into the downlink MIMO NOMA decode-and-forward(DF)relay system,an energy harvesting scheme based on dynamic power splitting is given,and the outage performance under perfect channel state information(CSI)is studied.Then,antenna selection and maximal ratio combining(MRC)are used at the transmitter and the receiver respectively.Meanwhile,the accurate outage performance and ergodic sum rate of the system are derived under the Nakagami-m fading channels.2.For the downlink MIMO NOMA-EH amplify-and-forward(AF)relay system,the accurate expression of the system outage probability is derived in closed-form with the AS scheme is adopted at both the transmitting and the receiving end.Then the performance of the AF relay system and the DF relay system are compared by simulation results.3.For the NOMA with fixed power allocation(F-NOMA)multi-relay system,the outage performance under imperfect CSI is studied with considering the existing of direct transmission links.The exact closed-form expression of the outage probability over the Nakagami-m fading channel is derived by adopting the RS scheme which can minimize the system outage probability.Meanwhile,the asymptotic expression and the diversity order of the outage probability are derived at high SNR region.Finally,simulation results verify the impact of channel estimation error on system outage performance.4.For the downlink CR-NOMA multi-antenna multi-relay system,a novel JRAS scheme is proposed,and the system's accurate outage expression is derived.At high SNR region,asymptotic outage expression and diversity order are also derived.Finally,simulations demonstrate that CR-NOMA can achieve a smaller outage probability than F-NOMA.Compared with the maximum and maximum(Max-Min-Max,AIA)JRAS scheme,the advantages of the proposed JRAS scheme on improving system outage performance are verified.