# Real-Time Precise Point Positioning during Outages of the PPP-B2b Service
## 3 Experiments and Results
### The Quality of the PPP-B2b Corrections Degradation over Time
#### 3.2.2 Accuracy of the PPP-B2b Extension Corrections  
In this study, the degradation of the PPP-B2b corrections within one hour was investigated using the data on DOY 192 in 2022. In our experiment, we assume that the track to the PPP-B2b signal was lost after we received the pair of clock and orbit corrections at a broadcast epoch on DOY 192. Then, the clock and orbit corrections at this epoch were used as the corrections for the following hour. The differences between these extended corrections and the actual PPP-B2b corrections were then calculated. Then, we moved to the next broadcast epoch and extended the PPP-B2b corrections for the epoch during the following hour, and we calculated the differences between these extended corrections and the actual PPP-B2b corrections. This procedure was repeated from the first epoch to the end epoch, and we thus obtained several time series with a time length of 1 h and an interval of the corrections update. With these results, we then calculated the RMSE of the clock and orbit differences at each epoch for each satellite.  
As depicted in Figures 10 and 11, when the last epochs of the orbit and clock corrections were used for the following hour, the RMSE of the extended orbit corrections showed an obvious increase with time. For the BDS-3 satellites, because the accuracy of the broadcast ephemeris is relatively high, the values of the orbit corrections were small (within the range of -10 to 10 cm), and the RMSE of the orbit error in the radial, along-, and cross-track directions was less than 6 cm even after one hour. However, for the GPS satellites, the RMSE of the extended orbit corrections in the radial, along-, and cross-track directions reached approximately 0.4 m, 0.8 m, and 0.8 m, respectively, after one hour. In terms of the clock correction, the RMSE was less than 1 ns and 2 ns for most BDS-3 and GPS satellites, respectively.  
To further investigate the quality of the extended orbit and clock corrections, a more comprehensive experiment was conducted with the data during the period of DOY 192-198 in 2022. The accuracy of the extended corrections was evaluated using the GBM products. As shown in Table 1, for the BDS-3 satellites, the accuracy of the extended orbit within 10 min can still be maintained at a similar level to the real-time PPP-B2b orbit, and the accuracy of the extended orbit of BDS-3 IGSO satellites was slightly worse than that of BDS-3 MEO satellites. For GPS satellites, the accuracy of the extended orbit deteriorated more rapidly than that of BDS-3, especially in the along- and cross-track directions. The mean RMSE of the GPS satellites reached 0.45 m and 0.8 m in the along-track directions after 10 min and 1 h, respectively. As shown in Tables 2 and 3, the mean RMSE and STD of the extended GPS satellite clock deteriorated much faster than the BDS-3 satellite. The  
Figure 9: STD of the BDS-3 and GPS satellite clock offset recovered with the PPP-B2b signals using the GBM orbit products as a reference during DOY 168–198 in 2022.  
mean STD values of the BDS-3 MEO, BDS-3 IGSO, and GPS satellites reached 0.17 ns, 0.20 ns, and 0.22 ns after 10 min, respectively.  
Figure 11: RMSE of the extended clock corrections of the BDS-3 and GPS satellites in the radial, along-, and cross-track directions on DOY 192 in 2022.  
Figure 10: RMSE of the extended orbit corrections of the BDS-3 and GPS satellites in the radial, along-, and cross-track directions on DOY 192 in 2022.