Research On The Downlink Pre-coding Technology In Massive MIMO Distributed Antenna Systems

With the advent of the mobile Internet era and its rapid development,business like voice and video,mobile games,high-definition live are enriching people' s lives and providing much convenience.However,it also challenge the acquisition and transmission of information about how to guarantee high speed and good quality.At the same time,the massive MIMO multi-antenna technology,which has attracted wide attention in recent years,has the characteristics of high spectral efficiency,high energy efficiency and high space utiliza-tion.The distributed antenna system can further improve the performance of wireless transmission by using remote antenna units.This paper mainly studies the downlink precoding technology in large-scale MIMO distributed antenna system.Firstly,this paper introduces the development history of mobile communication,the basic principle and the newest research status of MIMO multi-antenna technology,then briefly summarizes the characteristics of distributed antenna system,the classification of multiuser downlink precoding algorithm and some classical algorithms.Secondly,this paper studies the channel model and performance characteristics of distributed antenna system.Based on the fading characteristics of traditional wireless channels and the introduction of two com-mon channel models,this paper extend the channel model to distributed antenna system according to the characteristics of distributed antenna system.On the basis of this model,the coverage performance and ca-pacity performance of the distributed antenna system are analyzed emphatically.The simulation results show that the distributed antenna system has a wider coverage area than that of the traditional centralized antenna system,and the average channel capacity performance is better.Then,this paper studies the multi-user downlink linear and non-linear precoding techniques in distributed antenna system.In the linear precoding part,the classical precoding algorithm such as block diagonalization and the derived low complexity algorithm are introduced.On this basis,a simple QR algorithm based on channel expansion and a lattice reduction aided SIC algorithm are proposed.The simulation results show that the algorithm can further reduce the computational complexity without affecting the performance of the system.In the non-linear precoding section,the problem of high complexity of the spherical decoding process for traditional vector perturbation algorithm is improved by using the lattice reduction,which can obtain significant complexity advantage with slight performance loss.Finally,this paper studies the cooperative pre-coding technique in multi-cell distributed antenna system.Multi-cell systems need to suppress inter-cell interference as well as intra-cell interference.In this paper,we first introduce the traditional zero forcing algorithm,then extend the cascade precoding structure based on zero forcing in the literature by replacing the intra-precoding with the least mean square error vector perturbation algorithm.Then an improved algorithm which minimize the multi-cell total mean square error and leakage interference was proposed.The simulation results show that the above two algorithms are superior to the zero-forcing algorithm.In order to further reduce the performance gap with joint transmission,the paper also proposes the remote antenna unit and the antenna selection algorithm along with the user allocation algorithm to improve the service quality of the edge users.