Accuracy Evaluation and Comparative Analysis of Four Major GNSS Broadcast Ephemeris

  Objectives  The major global navigation satellite system (GNSS) includes global positioning system (GPS), global navigation satellite system (GLONASS), Galileo navigation satellite system (Galileo), and BeiDou navigation satellite system (BDS). The accuracy of broadcast ephemeris of the four major GNSS should be evaluated, and the evaluation results do not include systematic deviations.

  Methods  We download the mixed broadcast ephemeris and precise ephemeris of the multi-GNSS experiment (MGEX) for a total of 62 days from 1st September to 1st November in 2019, and select healthy satellite data from broadcast ephemeris every 15 minutes. After this preparation, we calculate the satellite position and clock difference of each GNSS system, then compare root mean square (RMS) of orbital position deviation, RMS of clock difference, and RMS of signal-in-space range error (SISRE) of all kinds of satellites with precise ephemeris. To correct the position of antenna phase center, the correction value should be selected corresponding to the generation of broadcast ephemeris. To eliminate the systematic deviation of clock difference, we make a quadratic difference on the average value of daily clock difference of single satellite.

  Results  The radial, along-track, cross-track position deviation and clock difference of the four major GNSS broadcast ephemeris fluctuate around 0 scale, indicating that the calculation results do not include systematic deviation, the methods of correcting the position of antenna phase center and eliminating systematic deviation of clock difference are correct and effective.

  Conclusions  The order of accuracies of the four major GNSS broadcast ephemeris from high to low is Galileo, GPS, BDS, GLONASS. With the development of each navigation system, the accuracy of broadcas ephemeris can be further improved.