The Analysis of Character of User Range Accuracy

Abstract

The new generation of Global Positioning System (GPS) plans to use user range accuracy (URA) as the integrity monitoring parameter of the signal in space. In the future, the system can forecast and monitor user range error (URE), which results from the signal-in-space error (SISE), including ephemeris error and clock error. By this way, system can reduce the space segment incidents’ impact for navigation users effectively. URA is an original parameter of GPS’s message, but its definition and application are changing all the time. In this paper, we firstly summary various changes of the URA, include not only the definition and the application, but also the refining of the index. Then, for the sake of finding the reasons of these changes, we make statistics on the IGS’s broadcast and precise ephemeris from 2002 to 2012. By analyzing the character of SISE and URE, we get conclusions below: because of the accuracy’s improvement of ephemeris and clock, the accuracy of URA must be improved. What’s more, the URE’s mean is non-zero, by the using of the concept of “bound”, the using of original URA will lead to an exaggerated bound so that it can’t reflect the integrity of the system. We can use the concept of error ellipsoid to explain this phenomenon effectively.