Research On User Clustering And Power Allocation In MIMO-NOMA Downlink Systems

Recently,with the rapid growth of the number of intelligent mobile terminals,the demand of communication transmission rate and access volume of communication equipment for mobile communication system is increasing as well.Besides,the full utilization of space resources and time/frequency domain resources by NOMA and MIMO technology provides a solid foundation for highspeed transmission and large-scale connection in current communication systems.Therefore,this thesis focuses on the basic theory of MIMO-NOMA cellular system and analyzes the process of signal transmission from base station to receiver in the downlink scenario and derives the relevant expressions in the transmission process.Based on these,the main work of this thesis is as follows:First of all,this thesis studies a beamforming technology and a user clustering scheme in the downlink MIMO-NOMA system.For beamforming,this thesis proposes an improved beamforming algorithm.The algorithm designs a beamforming vector of each cluster based on the channel interference matrices to relax the limit of antenna quantity and introduces a weight scaling factor in the decoding process to strengthen the required signal and eliminate inter-cluster interference;With regard to user clustering,this thesis proposes a clustering algorithm based on path loss value to improve sum rate of users in each cluster and compares the running time and sum rate performance of this algorithm with two common user clustering algorithms by numerical simulation.Simulation results show that the proposed algorithm improves the sum rate in each cluster effectively.Secondly,this thesis studies a power allocation strategy in the downlink MIMO-NOMA system.After analyzing and comparing the performance of common power allocation schemes,this thesis proposes a suboptimal power allocation strategy to improve the fairness of users in each cluster.This strategy narrows the search range of the power allocation coefficient of users in each cluster and ensures the sum rate advantage of the system compared with MIMO-OFDMA system under relevant constraints.The numerical simulation results show that the proposed user power allocation strategy can improve the fairness index of users in the cluster while ensuring the user rate.