## 5 Conclusions  
In recent years, there has been a rapid growth in demand for real-time precise applications. With a fully deployed BDS-3 constellation and available real-time precise satellite corrections contained in the real-time stream CLK93 transmitted by CNES, the real-time PPP with BDS-3 observations becomes feasible. Most importantly, the BDS-3/BDS-2 real-time PPP service can provide global coverage. We initially evaluate the global positioning performance of BDS-3/BDS-2 real-time PPP using the datasets from 147 stations in this study. In addition, the BDS-3/BDS-2 post-processed PPP results are also presented. For the purpose of completeness, the availability of BDS-3/BDS-2 constellations in the real-time situation is analyzed in terms of satellite numbers, PNT service rates and PDOP values, and the quality of BDS-3/BDS-2 real-time precise products is assessed. The corresponding results of GPS are also provided for comparative analysis. The joint use of BDS-3 and BDS-2 observations can offer a nearly full-time PNT service, except for some Americas areas where the BDS-3/BDS-2 PNT service rate can be decreased to 97.6%. The average number of visible BDS-2 and BDS-3 satellites changes from 6 to 19 on a global scale, whereas the corresponding varying range for the average PDOP values is 1.2-3.3. In the BDS-2 service regions (Asia-Pacific regions), the average BDS-3/BDS-2 satellite number is 13-19, while the maximum value for the maximum/minimum satellite number in these regions can be up to 23/17. Regarding the PDOP value, the average value is 1.2-1.8, and the minimum value for the maximum/minimum PDOP value can be as small as 1.5/0.9 in the Asia-Pacific regions. Except for C29, the availability of real-time precise satellite products exceeds 95.0% for all BDS-3 MEO satellites with a mean value of 95.1%. The average availability of real-time products is 97.0%/94.6%/93.4% for the MEO/IGSO/GEO satellites of BDS-2, respectively. Taking the SISRE as an indicator, the accuracies of precise satellite products in the real-time situation are at a similar level for BDS-3 and BDS-2 MEO satellites, which are 0.080 and 0.071 m, respectively. Larger SISRE values can be detected for the other two constellations, i.e., 0.477 m for BDS-2 GEO satellites and 0.109 m for BDS-2 IGSO satellites. In the static mode, the position accuracy of 1.8, 1.2 and 2.5 cm, and convergence time of 32.9, 23.7 and 32.8 min in the east, north and up directions can be achieved for BDS-3/BDS-2 real-time PPP, while the corresponding statistics are 6.7, 5.1 and 10.4 cm, and 66.9, 42.9 and 69.1 min in the three directions in the kinematic mode, respectively. The BDS-3/BDS-2 post-processed PPP improves the position accuracies by 2.6 and 0.9 cm on average, and shortens the convergence time by 21.9 and 10.6 min on average in the kinematic and static modes in comparison to the corresponding real-time PPP results, respectively. Compared with the BDS-3/BDS-2 results, almost all aspects of GPS results exhibit better performance. The global PNT service of GPS is always available. On a global scale, the average PDOP values change from 1.7 to 2.2, and the varying range is 8.8-10.7 for the average number of GPS visible satellites. The availability of GPS real-time precise satellite products can be up to 99.3%, and the average SISRE is as small as 0.039 m. Significantly better positioning performance can be achieved for the GPS real-time PPP, with a statistic of 0.6/0.8/1.5 cm for static positioning accuracies, of 13.4/7.1/15.9 min for static convergence time, of 2.9/2.6/5.1 cm for kinematic positioning accuracies, and of 22.2/14.5/23.4 min for kinematic convergence time in the east/north/up directions, respectively. Different from BDS-3/BDS-2, due to the high quality of real-time precise products, GPS real-time PPP only has slightly worse positioning performance than GPS post-processed PPP. **Author Contributions:** Conceptualization, L.P. and W.Y. ; methodology, L.P. and X.L. ; software, L.P. and X.L. ; validation, L.P., X.L. and W.Y.