## 6 Conclusions  
The following conclusions are drawn from the results of this study. 1. The RMS of the GPS broadcast ephemeris orbit errors in the along direction (0.92 m) is greater than that in the radial direction (0.17 m) and that in the cross direction (0.49 m). In addition, errors in the along direction are corrected most by the GPS PPP-B2b (by approximately 60%) among the three directions. The RMS of the GPS PPP-B2b orbit errors in the radial, along, and cross directions is 0.12, 0.34, and 0.26 m, respectively. 2. For BDS-3, the orbit errors of PPP-B2b are a few centimeters smaller than those of the broadcast ephemeris. The orbit errors of the IGSO satellite broadcast ephemeris are much greater than those of the MEO satellite broadcast ephemeris, and the orbit correction of the IGSO satellites is greater than the orbit corrections of the MEO satellites. The RMS of the MEO satellite PPP-B2b orbit errors in the radial, along, and cross directions is 0.10, 0.27, and 0.24 m, which is better than those of the IGSO satellites, 0.15, 0.32, and 0.41 m, respectively. 3. PPP-B2b correction improves the broadcast clock offset accuracy remarkably. For BDS-3, the average value of the STDs of the PPP-B2b clock offset is approximately 0.07 m. The accuracy is 70% higher than that of the broadcast ephemeris clock offset. For the GPS, the average value of the STDs of the PPP-B2b clock offset is approximately 0.03 m, i.e., the accuracy is 50% better than that of the broadcast ephemeris clock offset. 4. The smoothness and continuity of the navigation satellite orbit and clock offset error series are improved by the PPP-B2b service, which reduces the errors introduced by broadcast ephemeris data updates. 5. As the TJU-01 satellite is much higher than ground stations, it has a wider geographical range of PPP-B2b reception. Up to eight GPS satellites can receive the PPP-B2b correction at a certain epoch whereas up to seven BDS-3 satellites can receive the PPP-B2b correction. 6. More BDS-3 satellites than GPS satellites can receive PPP-B2b. The BDS-3 and GPS satellite constellations have different configurations, and the integrity of the GPS observations is lower than that of the BDS-3 observations. 7. As PPP-B2b mainly reduces errors in the broadcast ephemeris orbit in the along direction, the errors in the RT POD of the TJU-01 satellite using PPP-B2b in the along direction are smaller than those when using the broadcast ephemeris. 8. The accuracy of the RT POD of the TJU-01 satellite when using the GPS broadcast ephemeris is lower than that when using the BDS-3 broadcast ephemeris because the inter-satellite links improve the accuracy of the BDS-3 broadcast ephemeris, and more BDS-3 satellites than GPS satellites receive PPP-B2b. Moreover, the integrity of the GPS observations is lower than that of the BDS-3 observations. 9. The most accurate scheme is using the GPS and BDS-3 PPP-B2b for the RT POD of the TJU-01 satellite. The accuracy is improved by 5.1%, 43.9%, and 28.7%, respectively, in the radial, along, and cross directions relative to using the GPS and BDS-3 broadcast ephemeris. As the proportion of PPP-B2b correction reception increases, the accuracy improvement of PPP-B2b in the RT POD of the TJU-01 satellite increases. Conceptualization, M.L. and T.X. ; methodology, Y.S. ; software, Y.S. and K.W. ; validation, Y.S. and S.W. ; formal analysis, Y.S. ; investigation, M.L. and T.X. ; resources, M.L. and T.X. ; data curation, Y.S. ; writing--original draft preparation, Y.S. ; writing--review and editing, M.L. and T.X. ; visualization, S.W. and D.W.; supervision, M.L. and T.X. ; project administration, M.L. and T.X. ; funding acquisition, M.L. and T.X. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China (Grant No. 42204015), National Key Research and Development Program of China (2020 YFB0505800 and 2020 YFB0505804), and the Natural Science Foundation of Shandong Province (ZR2022 QD094).