Analysis of signal-in-space ranging error of GNSS navigation message

Abstract

The signal-in-space ranging error (SISRE) is a major factor that affects the accuracy of positioning and timing. It describes the projection of the satellite-broadcast ephemeris error and clock difference error in the average direction from satellites to stations. In this study, the size and characteristics of the broadcast ephemeris user range error (URE), clock difference error, and SISRE are evaluated with respect to GPS, Galileo, and BDS-3. The results indicate that the SISREs of Galileo, GPS, and BDS-3 are 0.14, 0.49, and 0.35 m, respectively, the broadcast ephemeris UREs of Galileo, GPS, and BDS-3 are 0.14, 0.27, and 0.09 m, respectively, and the clock difference errors of Galileo, GPS, and BDS-3 are 0.14, 0.41, and 0.35 m, respectively. In case of Galileo, the radial orbit error and the clock difference error exhibit strong correlation. Both these errors cancel each other, and the SISRE associated with Galileo can be effectively reduced. Further, obvious differences can be observed with respect to the clock difference error and SISRE in case of different types of GPS satellites. The clock difference error and SISRE of GPS will gradually decrease with the upgradation of satellites. The SISRE of BDS-3 exhibits different characteristics when compared with those exhibited by the SISREs of GPS and Galileo. First, the radial error of BDS-3 is less correlated with the clock difference error, which exhibits poor self-consistency. Second, the BDS-3 satellite-broadcast ephemeris URE is small, whereas the clock difference error is large. Furthermore, the broadcast ephemeris URE associated with BDS-3 is lower than those associated with Galileo and GPS. However, the contribution of the clock difference error associated with BDS-3 to SISRE is considerably greater than those of the clock difference errors associated with GPS and Galileo to SISRE. In this study, the sizes and characteristics of the SISRE of BDS-3, Galileo, and GPS are compared, indicating that signal-in-space accuracy of BDS-3 can be improved by reducing the clock difference error.