Research On The Broadcast Ephemeris Parameters Model And Its Fitting Algorithm

Broadcast ephemeris which provides navigation the satellites’ position information to the navigation users is an important component of the Navigation message of Satellites Navigation System, and its precision and stability directly determines the use’s navigation performance, Therefore, broadcast ephemeris parameters model and its application is a key technology of the satellite navigation system. This work has an in-depth study of the physical meaning and the fitting algorithm of the broadcast ephemeris parameters, and presents an feasible technology for solve the problem which exist in the application of GPS broadcast ephemeris parameters model using in mixed constellation consists of GEO,IGSO and MEO satellites. The main contents and Contributions of this work are as follows:(1) Having a comparative study of the GPS broadcast ephemeris parameters model and the GLONASS broadcast ephemeris parameters model. Through research of this paper, the GPS broadcast ephemeris parameters model have more clear physical meaning, simple satellite position calculation algorithm, and longer Prediction ability compared to GLONASS broadcast ephemeris parameters model, so that the Satellites Navigation System After the development of GPS and GLONASS use the Similar model as GPS.(2) Having a research on the Perturbation of the Navigation Satellites and its orbit variation characteristics. GPS broadcast ephemeris parameters model design based on orbit perturbation variation characteristics. The main perturbation force and their magnitude, and the long-term change of long periodic change and short periodic change characteristics of navigation satellites orbit are analyzed according to orbit analytic perturbation solutions. This work provide a Physical background for the designing of the broadcast ephemeris parameters model and the analyzing of the physical meaning of the parameters of the Existing models.(3) Having a in-depth study on the physical meaning of the parameters of GPS broadcast ephemeris parameters model. GPS broadcast ephemeris parameters model is designed for the MEO satellites, but the constellation of our satellites navigation system is consisted of GEO, IGSO and MEO three different types of satellites. There are many researches on the broadcast ephemeris parameters used in mixed constellation, but only few of them refer to the physical meaning of broadcast ephemeris parameters and the fitting problems of GEO satellites still have not been well solved. Through the study of this paper shows that: all of GPS broadcast ephemeris parameters have clear physical meaning for MEO and IGSO satellites, but its physical meaning may not so clear for GEO satellites as to kepler orbital elements used for GEO have singularities which are caused by small eccentricity and small inclination, if using the conventional method to fitting GEO directly, the correlation between the parameters will be strong and the fitting effect is bad than MEO satellite and IGSO satellite. Some parameters fluctuation range increase as orbital inclination decrease and also because of the three-body gravitational perturbation.(4) Having a research on the fitting algorithm of GPS broadcast ephemeris parameters model. Presenting that using coordinate rotation method can avoid the influence of the ill-posed problems caused by small inclination, improve the stability and reduce the fluctuation range of△n. Based on the non singularity Orbital elements fitting algorithm can avoid the influence of the ill-posed problems caused by small eccentricity, and can be applied to any eccentricity and any types of navigation satellites. Combination of the two algorithms used can solve the GEO satellites broadcast ephemeris parameters fitting problems very well.