Research On Cooperative Relaying Technique With Non-orthogonal Multiple Access

With the rapid development of mobile communication network,the shortage of spectrum resources becomes more and more serious,and the demand of mobile communications is growing,new services raise new requirements to the 5th generation(5G)wireless communications to support high rate,large capacity,low latency,high reliability,and massive connectivity.Non-orthogonal multiple access(NOMA)technology has become one of the most promising technologies in the new generation wireless communications because of its high spectral efficiency,this thesis focuses on the power-domain NOMA technology.Unlike orthogonal multiple access(OMA)technique,at the transmitter side,NOMA allows multiple users to transmit messages simultaneously with the same resource blocks(frequency domain,time domain and code domain).Successive interference cancellation(SIC)technology will be employed at the receiver side to decode the desired signals successively.Cooperative relaying technique can effectively expand the coverage of communication networks,reduce the outage probability and save the energy for data transmission by setting relay nodes,and thus enhance the communication performance.The combination of NOMA and cooperative relay technology can give full play to the advantages of the two technologies in the communication network,and further improve the effectiveness and reliability of communication networks.This thesis investigates the cooperative relaying system with NOMA,including the cooperative relay system with the uplink and downlink NOMA.The main contributions of this thesis can be summarized as follows:(1)A two-stage superposition coding scheme of the cooperative NOMA(CONOMA-TPSC)is proposed for the cooperative relay system with downlink NOMA.This scheme makes full use of the signals received at the relay,and effectively improves the sum rate and outage performance under this model.Firstly,the ergodic sum rate,outage probability and system throughput achieved by the CONOMA-TPSC scheme are analyzed with the imperfect channel state information(CSI)taken into account.Then,the correctness and effectiveness of the theoretical results are verified with the simulation and experimental results,in order to make a comparision with the existing schemes,the perfect CSI is considered in the simulation part,and the simulation results show that the proposed CONOMA-TPSC scheme can gain better system performance than the existing schemes.In the simulation section,the influence of power allocation coefficients at the relay on system performance is studied.Finally,the impact of channel estimation error on system performance under imperfect CSI is also analyzed.(2)A cooperative relaying system model with uplink NOMA(CFR-NOMA)is established,in which the user close to the base station works as a full-duplex(FD)relay to assist the communication between the far user and the base station.Firstly,the expressions in terms of ergodic sum rate and outage probability of the uplink CFR-NOMA system are derived.Then the expression of the optimal power allocation coefficients is derived at the outage probability minimization.Furthermore,considering that the far users are limited by the specific quality of service(QoS)requirements,the optimization problem with the maximum ergodic sum rate as the objective function is established,and the optimal power allocation coefficients of the near users are also analyzed.Finally,the correctness of the theoretical analysis is verified by simulation results.In addition,with the traditional uplink OMA and CHR-NOMA(where the far user works as half-duplex relaying)systems as benchmarks,the uplink CFR-NOMA system is analyed in the simulation section.The simulation results show that the proposed CFR-NOMA system gains much better performance than the traditional OMA and CHR-NOMA system.Besides,the influence of power allocation coefficients and self-interference signal on the system performance are discussed.