Research And Realization Of The Key Algorithm For Beidou Three-Frequency Differential Positioning

BeiDou satellite navigation system is a global satellite navigation system developed by China,unlike the GPS system of American and GLONASS system of Russia,it is the first satellite navigation system in the world that the whole constellation can broadcast three frequency satellite navigation signals.Multi-frequency observation is the trend of global satellite navigation system development in the future,the appearances of three-frequency observe value indicates that more combinative observations with longer wavelength,the smaller the ionosphere delay effect and smaller noise can be formed.Using these combinative observations can greatly improve the accuracy of cycle-slip detection and the success rate of integer ambiguity resolution.In view of the advantages of three-frequency observations,it is of great practical significance to study the BeiDou three-frequency algorithms.This paper mainly studied the three frequency measurements combination theory,cycle slip detection and repair algorithm,three frequency ambiguity resolutionalgorithm and BeiDou sidereal filteringalgorithm based on improved singular spectrum analysis(SSA),the main research work is as follows:(1)Three frequency observation equation of combined observations andthe expressions of its error were deduced,and the relationships between the errors are analyzed.At last,the optimal coefficients of the linear combination are selected by the standard of wavelength,ionospheric delay,and the observation noise.The results show that for those combinative observationswith longer wavelength,lower ionospheric delayand observation noise,the sum of its coefficient is zero;(2)Two cycle-slip detectionmethods based on triple frequency pseudorangeand phase observations are studied: triple frequency code-phase combination method and triple frequency geometry free phase phase combination method.A new cycle-slip detection method with low ionosphere considering pseudorange combination coefficients is proposed for the shortcoming that code-phase combination method is susceptible to the ionospheric delay.First,when constructing cycle-slip detectable amount,pseudorange combination coefficients with the minimum ionospheric delay coefficient are searched by setting the ionospheric delay coefficient threshold value of code-phase combination and taking the minimum standard deviation of estimated cycle-slip value as principle,the ionospheric delay effect of selected code-phase combinations are less than 0.06 cycle.Then,three linear independent cycle-slip detectable amounts are composed of two code-phase combinations with low ionosphere and one geometry-free phase combination.Finally,different sampling rate of the observation data are used for verification,the result shows that the cycle-slip detection method we proposed can be used to detect and repair observation data in different sampling rate,besides the delay effect of ionosphere is small and there is no existing insensitive cycle-slip combination;(3)Single epoch ambiguity resolution TCAR algorithm is studied,and the modified TCAR algorithm with low ionospheric delay is introduced.And then,a modified TCAR algorithm in which the noise level of triple frequency pseudoranges of BeiDou system are considered,not only does this algorithm optimize the coefficient of linear combination,but also reduce the noise of the combinative observations.At last,a group of BeiDou baseline(43km)observation data is used for verification.The results show that the ambiguity resolution success rate of the improved modified TCAR algorithm increases obviously;(4)BeiDou sidereal filtering algorithm based on improved SSA is studied,the embedding dimension is determined by phase space reconstitution Cao algorithm,and for the shortcomings of Cao algorithm an improvement is proposed,thus the computational efficiency and accuracy of the SSA method are improved.The repetitive cycle characteristics of different constellation satellites of BeiDou system are analyzed,and the repeat cycle of the BeiDou multipath error is estimated to be 86160 s.The results of BeiDou short baseline solution are processed by sidereal filtering based on singular spectrum analysis method and traditional wavelet method.The results indicate that the effect of SSA multipath filtering method are better than the wavelet method,and the multipath error in original coordinate sequence can be eliminated well.