# Real-Time Precise Point Positioning during Outages of the PPP-B2b Service
## 4 Discussion  
The introduction of the PPP-B2b service offers a new possibility for real-time positioning. To achieve real-time precise positioning, it is necessary to have access to continuously available, reliable, and accurate orbits and clocks products [23]. The PPP-B2b service requires that GEO satellites be visible, but in urban environments, these satellites may be blocked by the \"south wall effect\" or \"north wall effect\" for short periods, preventing users from receiving continuous precise orbits and clocks, which significantly impacts real-time positioning results. Therefore, it is important to consider strategies for maintaining real-time positioning during short interruptions of the PPP-B2b service when using this service. In this study, the characteristics of the PPP-B2b corrections during DOY 192-198 in 2022 were analyzed. The results demonstrate that the PPP-B2b corrections were subject to frequent jumps due to broadcast ephemeris updates and other factors. Specifically, the orbit corrections for the BDS-3 MEO, BDS-3 IGSO, and GPS satellites jumped on average 11, 26, and 17 times per day, respectively. Similarly, the clock corrections jumped on average 11 and 33 times per day for BDS-3 and GPS satellites, respectively. These jumps can make the data set used for predicting discontinuous, and can significantly affect the predictability of the PPP-B2b corrections. Several studies have demonstrated that combining corrections with broadcast ephemerides can improve continuity, which is also beneficial for predicting continuous periods [19; 20; 21]. However, systematic jumps and errors still occur for the PPP-B2b precision ephemerides. When a break occurs at the next ephemeris moment in which a jump occurs, it can still result in a lack of continuous data sets for predicting. To address this issue, we decided to use the last updated set of corrections before the outage occurred to compensate for the missing corrections. The accuracy of the extended corrections during DOY 192-198 in 2022 was evaluated using the GBM product as a reference to validate the effectiveness of this method. As shown in Tables 1-3, the accuracy of the extended corrections gradually decreased with increasing extension time, with similar accuracy for BDS-3 MEO and BDS-3 IGSO satellites, and GPS satellites showed a greater level of deterioration in accuracy compared to BDS-3 satellites. The mean RMSE of the extended orbit for BDS-3 satellites exceeded 30 cm with a 1 h extension, while the mean RMSE of the extended orbit for GPS satellites reached as high as 80 cm; the mean STD values of the extended clock for BDS-3 and GPS satellites were approximately 0.3 and 0.4 ns, respectively. However, when the extension time did not exceed 10 min, the mean RMSE of the BDS-3 satellite extended orbit was below 30 cm, and the mean RMSE of the GPS satellite extended orbit increased by 4 cm, 16 cm, and 8 cm in the radial, along-, and cross-track directions,  
Figure 15: Real-time PPP-B2b positioning accuracy in kinematic mode, including PPP-B2b service interruptions. respectively; in terms of the extended clock, the 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. Overall, the accuracy of the extended corrections remained within an acceptable range, indicating that the quality of the PPP-B2b corrections will not be significantly degraded in the short term and will maintain good accuracy. To further investigate the impact of extended corrections on PPP, the positioning accuracy of the simulated kinematic model using extended corrections was evaluated at five stations in and around China. As shown in Table 6, the results showed that there was a significant decrease in positioning accuracy at all stations as the interruption time increased, with the degree of this decrease being dependent on the region.