Navigation Satellite Broadcast Ephemeris Parameters And Fitting Algorithms

For the GNSS(Global Navigation Satellite System,the global navigation satellite system)navigation and positioning,It's necessary to provide a high precision satellite position and velocity in real time for the user to ensure that users of PNT(Positioning Navigation,and Timing services)normal operation.Broadcast ephemeris is an important module of the user's real-time navigation message,which can provide users with high precision satellite position and speed,and ensure the normal operation of PNT services.Therefore,for the construction of GNSS,the design of broadcast ephemeris is essential.The broadcast ephemeris parameters are obtained by the prediction of the orbit fitting,and the commonly used fitting algorithms are mainly the orbital root number method and the state vector integration method,and the typical representative is GPS and GLONASS broadcast ephemeris parameters fitting method.The orbit ephemeris and almanac parameters fitting method,due to its users a simple algorithm,high precision,the advantages of extrapolation ability,is widely used in GPS,BDS,GALILEO etc..However,due to the different constellations,the application of the orbital root number fitting method to different navigation systems has become a hot issue.In recent years,as the low orbit satellite has been rapid development in military reconnaissance,resource survey,disaster monitoring and other fields,which also put forward higher requirements on the orbit determination.By using LEO satellite as the enhanced navigation satellite is becoming a trend.In this paper,based on the background of spaceborne GPS receiver with LEO satellite,taking the CHAMP satellite as an example,the Chebyshev polynomial is used to discuss the orbit fitting of LEO satellite,and some useful conclusions are obtained.The main contents of this paper are as follows:(1)The development status and the latest developments of the four major satellite navigation systems are briefly introduced,and several common fitting algorithms for the parameter fitting of broadcast ephemeris are introduced.(2)The new GPS18 parameters applied to Beidou broadcast ephemeris parameters,the fitting accuracy of 16 compared with the traditional high an order of magnitude when the fitting time interval does not exceed 4h,the fitting precision of 16 parameters is less than 10 cm,the fitting precision of 18 parameters is less than 5cm.When the accuracy needs to be further improved,18 parameter broadcast ephemeris parameters are recommended.(3)For Beidou GEO satellite broadcast ephemeris parameters and user satellite position calculation to track rotation of the plane of this problem,the second kind of singularity free root number,to avoid a series of GEO satellite coordinates algorithm for user rotation,reduces the computational GEO user algorithm procedures,to a certain extent,improve the computational efficiency receiver.Using the Beidou GEO precise ephemeris for parameter fitting,the results show that the fitting arc section under the conditions of 2h,3H and 4H fitting is shorter,the fitting accuracy is higher,and the average fitting accuracy of 2h,3H and 4H is less than 0.1m.(4)Ephemeris parameters using second kinds of non singular root number design of the satellite,the calculation results show that the fitting precision of three satellites can meet the requirements of rapid positioning satellite and GEO satellite precision have been improved.(5)Using CHAMP satellite as an example,discussed the possibility of Chebyshev polynomial fitting is applied to the low orbit satellite broadcast ephemeris parameters,when choosing the appropriate fitting length,fitting order and fitting interval,low orbit satellite fitting can achieve high accuracy,using CHAMP satellite as an example,when the fitting order is less than 16 when fitting,length less than 1 hours,the fitting point interval is 10 s,the fitting precision can reach cm level.