Research On Channel Estimation In Massive Mimo Systems

With the development of the 4th generation of mobile communication technology,Multiple Input Multiple Output(MIMO)technology has gradually become widely used.The theory shows that increasing the number of antennas can bring higher radiation energy efficiency,higher robustness and system security.Facing the demand for the next generation of mobile communication technology,the large-scale antenna array will provide possibility for wireless communication to achieve faster and more stable performance in the future.In the meantime,millimeter-wave has drawn extensive attention due to its abundant spectrum resources,and its severe path loss also needs to be used in conjunction with a large number of antennas.As two key technologies of 5G,large-scale antenna array and millimeter-wave communication pave the way for the development of the next mobile communication technology generation.Meanwhile,they also bring new challenges as well.For the channel estimation,the increase of the antennas number makes the traditional channel estimation algorithm more complex and unsuitable,and channel modeling of millimeter wave becomes a completely new problem.Based on the hybrid antenna array and the millimeter-wave lens antenna array,the paper studies the channel estimation scheme.The main contents include two parts:In the first part,the advantages of the analog-to-digital hybrid antenna array are introduced.Based on this antenna structure,a Two-Dimension Multiple Signal Classification(2D-MUSIC)algorithm which can estimate the departure angle and the arrival angle,and the path gain estimation algorithm based on the Least Squares(LS)method are introduced.For the millimeterwave channel model with delay,the 2D-MUSIC algorithm will cause spatial spectrum ambiguity due to the existence of interference terms.This paper deduces that the IC-MUSIC algorithm based on interference cancellation can separate effective paths in millimeter-wave channels and estimate the parameters path by path,which can solve the problem of multipath with delay and reduce the cost of the hybrid array.In the second part,aiming at the problem of over complexity of ICMUSIC algorithm,this paper studies the structure of millimeter-wave lens antenna in massive MIMO system.By using the optical characteristics of highfrequency electromagnetic signals,a method of focus judgement is proposed to estimate the direction of arrival.Due to the channel reciprocity,the reverse communication can get the departure angle,estimate the path gain by the least square method,and finally reconstruct the channel matrix.This scheme takes advantage of the millimeter-wave lens antenna,provides lower algorithm complexity and a new idea for millimeter-wave channel estimation.Finally,the focus judgment method is improved for the possible extreme cases and channel estimation scheme based on interference cancellation is proposed.