Research On User Selection And Power Allocation Algorithm For Non-Orthogonal Multiple Access System

NOMA(Non-Orthogonal Multiple Access),as one of the candidate technologies of 5G,can improve the spectral efficiency and system capacity,and has attracted extensive attention.The essence of NOMA is the multi-user superposition of power domain,multiple users will be scheduling to superimpose and transmit on the same sub-band.So,the multiuser scheduling strategy will have a significant impact on the performance of NOMA system.PF(Proportional Fairness)Scheduling can achieve a good compromise between system capacity and user fairness,and it has considered to be used in NOMA.How to effectively select the user combinations and allocate the power factor in the scheduling process will have a significant impact on the scheduling complexity and system performance.The main research work of this thesis,will be divided into the following four parts.(1)The principle and mathematical model of NOMA system are described in detail,and the key technologies of transmitter and receiver are introduced.At the same time,the influence of each key technology on system performance is discussed.(2)The basic process of PF scheduling strategy in NOMA system is described,and the main principles and functions of user selection and power allocation in the scheduling process of the NOMA system are analyzed,which provide the theoretical basis for the following research.(3)The power allocation algorithm of NOMA is studied.Firstly,the optimal and suboptimal power allocation algorithms are analyzed,and the advantages and disadvantages of each algorithm are compared.For the optimal power allocation algorithm,it based on iterative traversal,needed to traverse the fixed power allocation space for all candidate users.And,the complexity is high,and there is a problem that the power factor can not suitable for the current user combination in the power allocation space.So,an improved strategy based on dynamic power allocation space is given.In this strategy,the influence of power factor on user's rate requirement and system throughput performance is analyzed,and combined with the principle of dynamic power allocation,the dynamic power distribution space is obtained to reduce the traversal range of power factor.Through the simulation analysis,the improvement strategy can better meet the access rate requirement of each user,and the performance is better than the suboptimal power allocation algorithm.At the same time,it can reduce the traversal range of 70% power factor when sending the signal to noise ratio is large enough.(4)For research the user selection algorithm.In the process of superimposing user matching,when the modulation combination of the superimposed user does not match the power factor,the reception performance will be deteriorated.So,we through research and analysis of the transmission performance and power threshold of each modulation method combination,and the better performance modulation combination and its corresponding power threshold was obtained.Finally,based on the above research results,the improvement strategy is given.By limiting the modulation scheme and the corresponding power factor in the user matching process,the number of PF criterion calculation can be reduced by 23%.