Research On Multiuser MIMO System Capacity Maximization With User Fairness

With the development of the fifth-generation mobile communication technology,the system’s demand for high spectrum utilization is becoming stronger and stronger.The issue of network energy consumption and fairness among users has also attracted more and more attention.Aiming at the issue of fairness-based energy allocation in multi-user MIMO systems,this thesis combines traditional communication scenarios and communi-cation scenarios assisted by intelligent reflecting surface(IRS)to jointly optimize trans-mit beamforming and intermediate reflection coding for intelligent reflecting surface.The specific research content is as follows:Firstly,consider the trade-off between fairness and system throughput in the multi-user multi input single output(MISO)scenario.In this thesis,the user signal-to-noise-plus-interference ratio(SINR)is used as a fairness index to maximize the sum rate of all users in the system under the power constraint of the base station,while satisfying that the communication rate of each user is higher than threshold constraints.This thesis establishes a fairness-based multi-user and rate maximization model under the condition of base station transmit power constraints.For this model,a Proximal distance-weighted Minimum Mean Square Error(PDA-WMMSE)algorithm is proposed,combining with Fast Iterative Shrinkage-thresholding Algorithm(FISTA)to improve the quality of the solution and the speed of convergence.The simulation results show that the computational complexity will be greatly reduced when the performance is close to that of the existing algorithm.Secondly,consider the multi-user MISO downlink communication system assisted by intelligent reflecting surface,and study the power control problem of the base station under the constraints of service quality for each user in the multicast communication sce-nario.For this problem,this thesis reduces the issue of minimum transmit power to jointly optimize the transmit beamforming and the phase of intelligent reflecting surface.By ex-ploiting the decoupling relationship of variables in the constraints,we use the alternate optimization method to optimize the variables in each block separately.The optimiza-tion of beamforming is solved by the PDA algorithm,while the optimization of intelligent reflecting surface’s phase is solved by iterative algorithm based on the difference of Con-vex function(DC)and the block coordinate descent(BCD)respectively.The simulation results show that the two algorithms proposed in this thesis show superiority in both per-formance and computational complexity.Finally,in view of the difficulty of hardware implementation of intelligent reflecting surface when the phase is continuous,this thesis considers the communication system with the assistance of the smart reflector with discrete phase and proposes a fairness model with the goal of minimizing transmit power.For this problem,this thesis proposes an efficient search algorithm based on BCD.The simulation results show that when the number of IRS is small,the proposed method can achieve better performance with less computation complexity than the existing methods.