# Investigation on Reference Frames and Time Systems in Multi-GNSS
## 2 Quality Check of Broadcast Orbits
### RSW Components of Coordinate Differences and Clock Differences  
Coordinate differences of broadcast vs. precise ephemeris of GPS are generally continuous. There are however occasional discontinuities, which affect mostly the along-track components. The coordinate differences in the radial and cross-track components may have an oscillatory pattern with a period of about 12 h. The average values of standard deviations are 0.15, 0.71, 0.34 m and 1.1 ns for the radial, along-track, cross-track and clock component, respectively. As to the satellite clocks, it is found that all satellites are equipped with atomic rubidium clocks, except G08 and G24, which are equipped with cesium atomic clocks and belong to block IIF. The average values of clock differences range between \(-\)3.4 and 2.0 ns. The magnitude of discontinuities is up to 0.3, 1.5, 0.2 m and 1 ns for the radial, along-track, out-of-plane and clock component, respectively. Mean values and standard deviations of coordinates and clock differences for each satellite are reported in Table 2. The complete time series of coordinates and clock differences for all GPS satellites are shown in Figure 11.  
GLONASS coordinate and clock differences show an oscillating trend, with a period of about 12 h, and discontinuities, which affect mostly the along-track and clock components. The average values of standard deviations are 0.48, 1.35, 0.74 m and 5.6 ns for the radial, along-track, cross-track and clock  
Figure 5: Representation of the offsets between Galileo (IOV, FOC) broadcast and precise reference system of CODE SP3. Figure 6: Representation of the offsets between BeiDou broadcast (IGSO, MEO) and precise reference system of CODE SP3. component, respectively. Average values of clock differences are different from one satellite to another, varying from \(-20\) to \(24\) ns. The magnitude of discontinuities is up to \(0.3\), \(3.0\), \(0.3\) m and \(8\) ns for the radial, along-track, out-of-plane and clock component, respectively. Mean values and standard deviations of coordinates and clock differences for each satellite are reported in Table 3. The complete time series of coordinates and clock differences for all GLONASS satellites are shown in Figure 11.  
BeiDou coordinate and clock differences show discontinuities, which affect mostly the along-track, especially for Medium Earth Orbit (MEO) satellites (C11, C12, C14), and clock components. Furthermore coordinate differences show an oscillating trend, with a period of about \(12\) h for MEO satellites and about a whole day for the other satellites (Inclined Geosynchronous Satellite Orbit--IGSO). The average values of standard deviations are \(0.43\), \(0.81\), \(0.63\) m and \(2.3\) ns for the radial, along-track, cross-track and clock component, respectively (except clock RMS of C11, for which a higher standard deviation is found, about \(27\) ns, due to two large discontinuities). Average values of clock differences are different from one satellite to another, varying from \(56\) ns to \(122\) ns. The magnitude of discontinuities is up to \(0.3\), \(1\) (IGSO) or \(3\) (MEO), \(0.3\) m and \(5\) ns for the radial, along-track, cross-track and clock component, respectively.