Research On Beam Tracking Algorithm For Mobile Millimeter Wave System

Currently,the frequency used by mobile communication network operators is concentrated below 6GHz.The increasingly depleted spectrum resources and low transmission rates have become the main problems restricting the development of communication technology.Millimeter-wave communication technology has naturally entered people’s view with its high frequency and large bandwidth.However,millimeter waves have higher path loss,so millimeter-wave communication systems need to use large-scale antenna technology for beamforming,aligning the beam direction with the main channel path direction to achieve beam alignment,allowing beam energy to converge at the direction of the main channel path,forming high beamforming gain,and compensating for the path loss of millimeter waves.At the beginning of establishing a communication link,there is no or only a little of initial information about the channel direction,and all angular spaces need to be scanned for initial beam alignment,called beam searching.Classical beam searching algorithms are generally divided into exhaustive search algorithms and hierarchical search algorithms.After establishing the communication link,it is necessary to maintain this beam alignment in a mobile environment,make the beam direction always tracks the main channel path direction,called beam tracking.There are many problems with millimeter-wave beam tracking algorithms,such as large time overhead and unstable tracking accuracy.To address these issues,this paper proposes two algorithms that can adaptively adjust the tracking frequency based on the rate of change of the angle of the main channel path,while reducing the tracking overhead and ensuring the accuracy of beam tracking.The paper first further studies the EKF based beam tracking method and develops an EKF based adaptive beam tracking algorithm,the AT-EKF(EKF Based Adaptive Tracking)algorithm.The proposed AT-EKF algorithm takes the decay of the SNR after beamforming of the received signal as the main basis for decision-making on whether the channel angle needs to be tracked,and 1)estimates the minimum tracking interval based on the channel angle change model,and 2)estimates the maximum tracking interval according to the historical channel angle information,reducing the probability of losing tracking and ensuring tracking reliability.In addition,the algorithm uses the ratio of the auxiliary beam pairs’ measured signal as the measurement equation for the EKF estimator,which reduces the error accumulation phenomenon caused by using EKF as the angle estimator,reduces the computational complexity of the EKF estimator,and extends the effective tracking time of the algorithm.Based on AT-EKF,the paper further proposes an adaptive beam tracking algorithm based on IEKF(Iterator Extended Kalman Filter),the AT-IEKF(IEKF Based Adaptive Tracking)algorithm.This algorithm uses IEKF as the angle estimator,which has higher estimation accuracy compared to EKF.This algorithm also uses a more reasonable angle change model and adopts model reconstruction and estimation of the variance of the random term in the angle change model to solve the problem of the algorithm’s dependence on the angle motion model.In addition,this algorithm also solves the problem of the observation equation noise variance being damaged in the AT-EKF algorithm.Through two experiments,including simulating the angle change model under a statistical channel model and modeling the real channel angle change model with high-precision ray tracing software,the performance of the algorithm in adaptive beam tracking is verified.