Relay Hybrid Beamforming Algorithm For Large-scale MIMO System

Large-scale multiple input multiple output(MIMO)system involved technologies in millimeter wave become a research hotspot in the field of wireless communications,which have received extensive attention from scholars in this field.Because of the heavy attenuation of millimeter wave,large-scale MIMO system covers small area.So,the introduction of relay can effectively provide wider coverage.In small-scale MIMO relay systems,all-digital technology is the most widely used method.However,in large-scale MIMO systems,digital beamforming is difficult to apply in practical situation because of high costs and heavy energy consumption.This paper focuses on the relay hybrid beamforming design in millimeter wave large-scale MIMO systems.The main content of the paper is as follows: 1.We first introduce the basic principle of the analog/digital hybrid beamforming technology in millimeter wave large-scale MIMO system and discuss the necessity of hybrid beamforming technology.Next,we explain the system framework of the hybrid beamforming in the relay large-scale MIMO systems,furthermore we establish a minimum mean squared error(MMSE)-based relay hybrid beamforming mathematical model.2.According to the base station,relay,and user three-terminal equipment,the established full-connection structural optimization model is decomposed into three optimization sub-problems,and the original optimization problem is approximated by adopting the method of alternately solving three sub-problems.Since the analog beamforming optimization sub-problems have non-convex constant modulus constraints,we use linear constraints instead of constant modulus constraints to relax it into a convex optimization problem,and propose an iterative successive approximation(ISA)approximation algorithm to attain the high-approximate optimal solution to the sub-problem.We prove that the ISA algorithm converges to Karush-Kuhn-Tucker(KKT)point of the original problem theoretically;the simulation results verify the effectiveness of the proposed method.3.In order to apply the massive MIMO relay hybrid beamforming algorithm in the scenario where is no direct signal path,the relay hybrid beamforming technology is studied for the scenario where is no direct signal path,corresponding optimization model is established.an improved algorithm based on 2 is used to solve the optimization model.Simulation results show the proposed method has poor system performance with 2.