Accuracy Analysis of GNSS Broadcast Ephemeris Orbit and Clock Offset

  Objectives  At present, the accuracy analysis of global navigation satellite system(GNSS) broadcast ephemeris mostly focuses on the accuracy analysis of single system or short time, there is left relatively certain limiations.

  Methods  We present a comprehensive comparison and analysis of the current broadcast ephemeris accuracy for multiple global navigation satellite systems (GNSS). The analysis is performed by comparing GNSS broadcast ephemeris with corresponding precise ephemeris. The long-term accuracy change of the broadcast ephemeris of various systems is analyzed using the GNSS broadcast ephemeris with the corresponding precise ephemeris from 2014 to 2018.

  Results  The experimental results show that the orbit and clock offset accuracy of the broadcast ephemeris from the global positioning system (GPS) is the most stable during five years. The broadcast ephemeris of global navigation satellite system (GLONASS) has better orbit accuracy stability, but its clock offset accuracy has a large dispersion. The Galileo satellite navigation system (Galileo) has benefited from the large number of launches and operations of satellites with full operational capability. The orbit and clock offset accuracy of its broadcast ephemeris have greatly improved. In particular, the accuracy of orbit in tangential and normal directions and clock offset accuracy has surpassed that of GPS. The orbit accuracy of the broadcast ephemeris of the BeiDou navigation satellite system (BDS) has a large dispersion, and its accuracy of the clock offset shows instability. The stability of orbit and the clock offset accuracy of the broadcast ephemeris from the quasi-zenith satellite system (QZSS) is the worst. The current accuracy of the broadcast ephemeris for five systems is compared and analyzed using the one-year (2018) GNSS broadcast ephemeris and the corresponding precise ephemeris.The signal-in-space ranging errors(SISRE) considering the contribution of satellite orbital error and clock offset error for GPS, GLONASS, Galileo, BDS, and QZSS are 0.806 m, 2.704 m, 0.320 m, 1.457 m, and 1.645 m, respectively. The SISRE considering only the contribution of orbital error for GPS, GLONASS, Galileo, BDS, and QZSS are 0.167 m, 0.541 m, 0.229 m, 0.804 m, and 0.675 m, respectively.

  Conclusions  These indicate that the broadcast ephemeris of the Galileo has the highest overall accuracy, followed by GPS, BDS, QZSS and GLONASS. The GPS broadcast ephemeris has the highest orbit accuracy, followed by Galileo, GLONASS, QZSS and BDS. Moreover, we found that the clock offset accuracy of the new kind of satellite is generally better than that of old kind of satellite in GPS satellite broadcast ephemeris.