Research On Theory And Method Of BDS Clock Offset Prediction Model Based On Semi-parameter Estimation

The navigation satellite is a time-based ranging system.The high-precision spaceborne atomic clock is the basis of the global navigation satellite system.By estimating and predicting the star clock parameters of the on-board atomic clock,the time parameters of the precise on-board atomic clock are obtained.It is significant to synchronize the time synchronization of the navigation system and to improve its related service performance.Since the satellite clock offset is obtained based on the multisatellite joint orbit determination,it will be affected by the satellite orbital error coupling.In addition,there is a certain systematic deviation in the mechanical modeling of the Beidou satellite,especially the optical pressure model.It can be known from the law of error propagation that all these will lead to errors in the clock offset model,which makes the fitting effect and prediction accuracy of the conventional clock offset model have a certain degree of influence.Furthermore,the residuals of the satellite clock offset contains other colored noises other than white noise,making it difficult for conventional prediction models to fit these nonlinear colored noises with no significant law.These model errors will also be affect the estimation of the satellite clock offset parameters and the accuracy of the satellite clock offset prediction.Firstly,in view of the high frequency of abnormal data such as clock jump and gross error in Beidou satellite clock data,this paper comprehensively considers these anomalous data and system errors.First of all,based on the improved clock offset model,the compensation least squares principle and the method of extremum are used.The solution method deduces the relation expression between the parameter and nonparametric estimation values before and after the separation of abnormal data and the correction value of the corresponding observation value,and realizes the fixed value of the abnormal data,parameter solution and system errors separation.On this basis,the Cook distance is introduced,and the Cook distance and the mixed Cook distance of the parameter component and the non-parametric component are used to determine the location of the outliers.In addition,some parameters selection methods(Q and C)and corresponding processing measures are given.Correspondingly,the positioning and setting of the satellite clock offset data and the separation of some systematic errors are realized.Last but not least,using the Beidou satellite precision clock data provided by the GNSS Center of Wuhan University with a sampling interval of 5 min,the experimental method is compared with the commonly used methods.The experimental results show that the proposed method can effectively identify and process the outliers of satellite clock offset data,and effectively overcome the shortcomings of the empirical threshold clock offset data detection method.Moreover,the method has a good detection effect for the abnormal clock offset of smaller magnitude,which enriches the existing BDS clock offset data quality control methods to a certain extent.Secondly,with respect to the influence of model errors in conventional Beidou clock offset prediction models,a semi-parametric adjustment model BDS satellite clock offset prediction method considering model errors is proposed in this paper.At first,the model errors of the conventional Beidou clock offset prediction model is analyzed.Meanwhile,the relationship between polynomial model,polynomial model with additional periodic term correction and its periodic correction term is explored in detail.Then,considering the model errors,combined with the physical relationship between phase,frequency,frequency drift and its period in the clock sequence,the conventional clock offset prediction model is improved.Using kernel estimation and comprehensive least squares,the corresponding parameter solutions of the prediction model and the estimation of its model error are derived,and the dynamic correction of the error of the clock sequence model is realized.At last,the Beidou satellite precision clock data provided by the GNSS Center of Wuhan University with a sampling interval of 5 min was used to compare the prediction method with the commonly used methods.The experimental results show that the prediction method of this paper can achieve better correction effect on the model errors of BDS satellite clock offset,and effectively overcome the inaccuracy of clock offset correction.The average forecast accuracy of the Beidou satellites at 6h,12 h and 24 h is 27.13%,37.71% and 45.08% higher than the conventional Beidou clock offset forecast model respectively;the average model improvement rate was 16.92%,20.96% and 28.48%,respectively,enriching the existing BDS satellite clock offset prediction method.Thirdly,the effects of compensated semi-parametric method and semi-parametric kernel estimation method in correcting the systematic errors(model error)of commonly used satellite clock offset are compared,and the relevant factors affecting the solution effect of the model are explored in detail.In addition,the performance of these two methods in BDS satellite clock offset modeling and short-term prediction is deeply explored.At the same time,the model error sequences separated by the two methods are analyzed,and some suggestions are given based on the application scope of these two methods.Finally,the research work done in this paper is summarized,and the existing deficiencies in it are concluded and combed.Furthermore,the prospect of the following work is given.