LEO Satellite Broadcast Ephemeris Model And Algorithm

Low earth orbit(LEO)satellites broadcast navigation augmentation information and navigation signals will improve the positioning accuracy and integrity of navigation systems and achieve backup capabilities of navigation systems.At the same time,it is possible to provide trusted and continuous navigation services in a complex environment with strong interference and strict obscuration since the LEO satellites signal can be really strong.This article focuses on the theme of LEO navigation augmentation satellites,which involves the design of LEO satellite constellations and the design of LEO satellite broadcast ephemeris parameters.The main work and achievements are as follows:(1)80 satellites with orbit altitude of 1000 km are selected to form a LEO satellite constellation.The satellite constellation configuration is W80/8/1,and the orbital inclination of the satellites is 55°,which can achieve global coverage of 90% apart from the high latitudes.The PDOP values of LEO satellites in the 80 degrees north and south latitude range from 1 to 10.Also it is demonstrated that the LEO constellation augmented the BDS global system(3GEO+3IGSO+24MEO).Simulation results show that the addition of low-orbit satellite constellations reduced the maximum PDOP value of the BDS constellation by 20.5%,the minimum PDOP value by 13.5%,and the average PDOP value by 17%.(2)GPS 16/18 parameters are applied to LEO satellites of 500 km to 1500 km,the fitting residuals are between 2cm and 20 cm.The spectrum analysis of the CHAMP satellites shows that the satellite orbital semi-major axis has a T/2 short-cycle term,and the orbital eccentricity and perigee apices have T/3 and one short-period terms.Based on this,a 22-and 24-parameter LEO satellite broadcast ephemeris was designed.The simulation and actual measurement results show that under the 22-parameter 20-min fitting time period,the URE of the satellite with 500 km orbit altitude is better than 6cm,the URE of 1500 km orbit altitude is better than 2cm,and the URE is better than 1cm with 10 min arc length.When the orbital altitude is 500 km,the 22-parameter and 24-parameter fitting accuracy is equivalent under the 20-minute fitting time.When the orbital altitude is 1500 km,the 24-parameter fitting accuracy is better than 4mm.In order to reduce the computational complexity and the data occupation ratio,a 22-parameter low-orbit satellite broadcast ephemeris is proposed.Also the number of occupied bits of 22 parameters is given accord ing to the GPS 16/18 parameter.(3)The LEO satellite broadcast ephemeris in the form of SP3 is proposed.The ephemeris form is intuitive,the user algorithm is simple,and the satellite position can be obtained using the Lagrangian interpolation algorithm.To obtain satellite positions of 30 s and 1s time intervals,with the 10 minutes arc,the 1000 km low-orbit satellite interpolation results can achieve a precision of cm-level after the interpolation order is greater than 14 steps.With the 5 minutes arc,when interpolation order greater than 8 the result can reach the cm-level of accuracy.The analysis of the message format shows that the SP3 file in ASCII format broadcasts 720 bits per epoch,and the number of bits occupied in the binary file format is 232,which reduces the data load by about 66%.