Research On The Detection And Repair Method Of Cycle Slip In Beidou Positioning

BeiDou Navigation Satellite System(BDS)has started network of the Beidou-3 satellite.It will provide services for countries which are along and around the Belt and Road Initiative by the end of 2018.The application of topographic mapping,vehicle navigation,weapon guidance and bridge monitoring ha ve put forward higher requirements for the positioning accuracy of the BDS in modern society.C ycle slips which occur in BDS carrier phase data are the main factor that affect the positioning accuracy of the BDS.So,it's necessary to detect and repair cycle slips.This paper takes cycle slips as the research object,experiment is designed to collect and analyze the BDS satellite signal,the methods of cycle slips detection and repair are researched.The main achievements of this paper are listed as follows:(1)The observation model of cycle slips,the definition of cycle slips and the error of cycle slips are introduced.The experiment is designed to collect the BDS signal,and the BDS signal is analyzed in the time domain.The analysis results show that the epoch difference noise of the pseudo-range/phase measurements will flood 1~2 cycle slips.(2)The application of wavelet and Empirical Mode Decomposition(EMD)which detect cycle slips in single-frequency data are analyzed.Aiming at the problem that the mode mixing phenomenon which caused by EMD is not conducive to detect small cycle slips,the Ensemble Empirical Mode Decomposition(EEMD)is used to decompose the single-frequency signal,more information of cycle slips is highlighted.Aiming at the problem that the end effects which caused by EMD and EEMD can reduce the detection precision of cycle slips,the improved Intrinsic Time-scale Decomposition(ITD)method is used to decompose the signal of cycle slips.Then,the component signals which include cycle slips are screened out from all component signals which decomposed by the two methods.Finally,detect the epoch where cycle slips appear by calculating the maximum point of Hilbert amplitude spectrum of the IMF components which are selected.The experimental results show that the cycle slips are decomposed into multiple component signals by the two methods and the epoch which tiny 1 cycle slips can be detected accurately by Hilbert spectrum.(3)In the application of cycle slips detection,the method EEMD and the improved ITD can only detect the position of the cycle slips,but not calculate the size of the cycle slips directly.In order to solve the problem,component signals are used as training samples,the method Particle Swarm Optimization(PSO)is used to optimize parameters of Least Squares Support Vector Machine(LS-SVM).The optimized LS-SVM is used to make a regression prediction.The cycle slips are determined and repaired by calculating the difference between the measured value and the predicted value.The experimental results show that this method can repair the cycle slips which appear in single frequency carrier phase measurement effectively.(4)The code-phase combination method and Geometry-free phase combination method are analyzed.In order to improve the detection accuracy,the combination coefficient is optimized.Finally,combined the two methods to make experiments.The results show that the combination method can effectively detect and repair cycle slips.