Research On Time-frequency Characteristics And Prediction Algorithm Of GNSS Satellite Clock

With the globalization of BeiDou satellite systems,a network providing global multi-frequency and multi-GNSS service will be formally established.More satellites and satellite atomic clocks with higher quality are the foundation of high-precision and timeliness for Positioning Navigation and Timing.Currently,there are still many theoretical and practical problems in the time-frequency characteristics performance,and clock offsets prediction of on-board atomic clocks for GNSS satellites,especially of BDS satellites.In order to solve the problem of GNSS atomic clocks offset prediction unstable,and to improve the precision and reliability of GNSS equipment PNT services.Through the real-time services are susceptible to issues such as the influence of satellite atomic clock anomalies,the time-frequency characteristics and time-varying regularities of each satellite atomic clock have been obtained through long-term characteristics analysis and quality evaluation.To provide the theory and model basis for the real-time monitoring of satellite clocks,clock prediction,and performance compensation.In the research,satellite clock products are used to study on characteristics,error models,prediction methods and real-time PPP of the GNSS satelite atomic clocks.The main work and contributions of this research are as follows:(1)The basic models of the characteristics evaluation and clock offset prediction of satellite atomic clocks are summarized.The polynomial mathematical function model used for characteristic and performance evaluation and the most commonly used model of clock prediction function are introduced.And the parameter estimation model mainly introduces sequential least squares and Kalman filtering.(2)Based on long-term precision clock offset data of the BDS-2,BDS-3 experimental,Galileo and GLONASS satellite atomic clocks phase,frequency,frequency drift,fitting residual and time-frequency stability of the onboard satellite clocks have been evaluated.Compare and contrast satellite atomic clocks characteristics and service quality between different systems.Analyzed the frequency fluctuations of some BDS satellite atomic clock subsistent period of half a year,and the detection method for the switching of the main and standby clocks of the BDS satellite atomic clock has been proposed.The statistics of satellite clock switched situation has given.(3)The stability indexes of BDS-2,BDS-3 experimental,Galileo,and GLONASS satellite atomic cloaks were evaluated by Allan variance and Hadamard total variance,and the stability characteristics of individuals' satelite clocks were analyzed.(4)An improved prediction model for BDS-2 satellite clocks is proposed in order to improve the precision and stability of real-time prediction clock offsets.Through long-term spectrum analysis reveals the abnormal period term and noise sequence characteristics of the BDS-2 individuals satellite clocks.And based on quadratic polynomial,the periodic term,starting point deviation,adaptive weight function,and BP neural network correction have been added.Solving the problems exist in BDS-2 satellite clocks such as unwell-distributed,poor heterogeneity of geometric configuration and worse stability.(5)In real-time positioning,the receiver clock will suddenly appear the clock jump,which results positioning accuracy loss and repeatedly re-convergence.The clock jump detection compensation method based on the additional receiver clock difference real-time prediction model is proposed.The sliding window is established by the receiver clock epoch-difference and real-time prediction clock offset which could effectively detect and repairs the receiver clock jump to improve the receiver clock offset sequence accuracy and the stability of the positioning result.The results verify the effectiveness of the method.(6)The broadcast ephemeris and State Space Representation are used in the algorithm of recovering real-time precise orbits,clock,and ionosphere.Aiming at the high accuracy,high timeliness and a wide range of BDS-2 Satellite-Based Augmentation System,the accuracy and performance of the global and Asia regional,single-and dual-frequency positioning,and real-time product accuracy has been evaluated.And the positioning accuracy and the quantization error caused by enhanced message were comprehensively evaluated.