Preliminary Analysis of URA Characterization for GPS Real-time Precise Orbit and Clock Products
Chun Cheng, Yuxin Zhao, Liang Li, Jianhua Cheng, Xiangyu Sun, Harbin Engineering University, China
International GNSS Service (IGS) organization launched an open-access Real Time Service (RTS) products for Real Time Precise Point Positioning (RT-PPP). At present, RTS mainly includes the real-time precision orbit and clock streams from different analysis centers of IGS and the combined solutions. Although User Range Accuracy (URA) is reserved according to Radio Technical Commission for Maritime services-State Space Representation (RTCM-SSR) protocol, none of the real-time stream products broadcast URA yet. As an indication of quality of correction products, the value of URA is of great importance for the quality control of RT-PPP to obtain the highly precise result, and URA is significant to obtain a reliable result for user who utilize the algorithm of integrity monitoring. In order to research the characteristics of URA, we must clarify User Range Error (URE) of the real-time precision orbit and clock products, and the distribution of satellites’ orbit and clock errors have to be characterized. In this paper, we mainly analyze the real time precision orbit and clock product from Centre National d’Études Spatiales (CNES). The accuracy and error distribution characteristics of real-time precision ephemeris can be obtained firstly. The result has shown that the radial, along, cross of orbit errors is about 2cm, 3cm, 2cm, the clock difference is about 0.15m, which has no correlation with satellite type. The distribution of orbit errors follows Gaussian distribution perfectly. In contrast, the distribution of the clock errors do not satisfy Gaussian distribution. And then, we analyzed the correlation among the radial, along, cross error of orbit and clock error. There is a positive correlation between the clock and the radial error of orbit. The radial and along error of orbit have a negative correlation. We studied the computational strategy and characteristics of URE. URE is mainly affected by satellite clock errors, and do not satisfy Gaussian distribution. URA value is about 0.03-0.35 m getting from Empirical Cumulative Distribution Function (ECDF) of URE or Root Mean Square (RMS) estimation of URE. URA has no obvious correlation with satellite type, but it is different with different satellites, which need to be accounted for high precision and high integrity navigational applications.