Research On The Mechanism And Mitigation Algorithm Of GEO Satellite Multipath Error

BeiDou satellite navigation system(BDS),as one of the four major international satellites navigation system,is following the "first regional,after the global" plan for rapid development.BDS space constellation firstly adopts the GEO+IGSO+MEO mixed constellation structure.Although this mixed constellation structure makes the BDS achieve a larger area coverage by launching a small number of satellites,the high-orbit satellites such as GEO and IGSO bring a lot of unfavorable factors.Especially,GEO satellite with a relatively static characteristic not only reduces the correctness of the orbit parameters solution,but also it causes the “standing” multipath in the radio signal,which weakens the GEO satellite orbit determination accuracy,and even reduce the BDS system service performance.At present,the researches on the mechanism of multipath effect of BeiDou GEO satellite are not deep enough,and the corresponding multipath mitigation algorithm are also not mature enough.Based on the BeiDou multipath error of major science and technology projects,this paper has studied the above problems by collecting a large number of measured data,and the innovative research results are as follows.A method for analyzing the multipath fading characteristics of GEO satellites is proposed.In order to study the fading characteristics of the BeiDou GEO satellite multipath error curve,the paper establishes the relationship between the multipath fading frequency and the satellite orbital parameters by building the multipath reflection mathematical model.Meanwhile,the Kepler multipath fading factor(KMPF)is defined,which can be used to analyze the multipath fading of the GEO satellite.We analyze the effect of orbit parameters on the KMPF by simulation experiments,and a significant conclusion that KMPF factor can be used as an important parameter to analyze the multipath fading characteristics of GEO satellites can be obtained.Finally,the KMPF factor is used to analyze a large number of measured data.The experimental results show that the multipath fading characteristic of GEO satellite has a strong correlation with the trend of KMPF curve.The slow fading interval of the GEO satellite multipath error curve corresponds to the first subsidence point of KMPF,and the fast fading interval corresponds to the second subsidence point of KMPF.In summary,the KMPF can be used to analyze the multipath fading characteristics of GEO satellite,and the GEO characteristics of satellite multipath fading are closely related to satellite orbit.A wavelet-denoising algorithm for satellite multipath error based on 2-Fold Cross Validation is proposed.In order to solve the disadvantages of traditional multipath noise denoising algorithm,such as low adaptive performance,poor signal extraction performance,the proposed algorithm based on the method of statistical data classification can assistant the discrete wavelet decomposition algorithm to obtain an appropriate decomposed layers.During this process,because the algorithm does not need to analyze the noise characteristics of the raw multipath error data,this algorithm not only has a low computational complexity,but also have a high signal extraction performance.Comparing with the traditional algorithm,the simulation results show that the proposed algorithm in the correlation coefficient,root mean square error and smoothness and other performance indicators are improved by 7.2%,32.8% and 23.8%.A spacecraft reflection model of GEO satellite is proposed,and a numerical optimization algorithm for calculating the reflection parameters is designed.The proposed signal reflection model can accurately fit and predict the real multipath signal,which further clarifies the mechanism of multipath error of GEO satellite.Based on the 2-Fold Cross Validation wavelet denoising algorithm proposed in this paper,the GEO satellite multipath data collected from two sites with similar open terrain are compared and analyzed.The results are as follows:(1)BeiDou GEO satellite code multipath measurement with a slow fluctuation and a certain periodicity shows a correlation with the satellite elevation angle.(2)The signal reflection on the surface of BeiDou GEO satellite is one of the causes of multipath effects.According to the satellite surface reflection model,the numerical algorithm of the reflection parameter is designed,and the reflection model is also verified by the measured data.Experiments show that the proposed multipath reflection model based on the measured data can predict the real multipath error signal of BeiDou GEO satellite,and to a certain extent the proposed model explain the mechanism of BeiDou GEO satellite multipath generation.A multipath mitigation algorithm based on wavelet transform sidereal filtering and a multipath mitigation algorithm based on GEO satellite reflection model are proposed.The experimental results show that both methods can effectively suppress the multipath error of BeiDou GEO satellite in different situations.According the research,the results are as follows:(1)The multipath suppression algorithm based on wavelet transform sidereal filtering not only improves the mitigation performance for multipath error(10.18% ~ 17.04%)compared with the traditional star day filter,but also it can be used in the real-time situation.(2)Because of using the satellite broadcast ephemeris parameters,the multipath suppression algorithm based on the GEO satellite reflection model can effectively predict the time-frequency patterns of the multipath error signal with longer time interval.This algorithm not only extends the "short-life" of the traditional sidereal filtering,but also the suppression performance for the GEO satellites multipath error has increased by 7% to 13%.