## 4 Discussion  
According to the above analysis, the consistency of the precise products from different ACs is usually at a centimeter level, sub-decimeter level and decimeter level for the GNSS/RNSS MEO, IGSO and GEO constellations, respectively. Except for the WHU products for GPS and GLONASS satellites, the SISRE consistency among various post-processed precise products is usually better than 1.5, 3.0, 2.5, 4.5, 4.0, 22.5, 10.5, 32.5 and 15.5 cm for the GPS, GLONASS, Galileo, BDS-2 MEO, BDS-3 MEO, BDS-2 GEO, BDS-2 IGSO, OZSS GEO and QZSS IGSO satellites, respectively, while the increased SISRE difference between the real-time and post-processed precise products is usually smaller than 3.0, 6.0, 5.5, 5.5, 7.5, 55.5 and 9.5 cm for the GPS, GLONASS, Galileo, BDS-2 MEO, BDS-3 MEO, BDS-2 GEO and BDS-2 IGSO satellites, respectively. As to the benefits from multi-system combination for PPP processing, the convergence time in both static and kinematic modes as well as the kinematic positioning accuracy can be continually improved \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**System Combination**} & \multicolumn{3}{c}{**Convergence Time (min)**} & \multicolumn{3}{c}{**Positioning Accuracy (cm)**} \\ \cline{2-7}  & **East** & **North** & **Up** & **East** & **North** & **Up** \\ \hline G-PPP & 19.8 & 13.5 & 22.7 & 3.3 & 2.6 & 5.2 \\ R-PPP & 82.7 & 68.3 & 98.0 & 7.3 & 4.6 & 9.8 \\ E-PPP & 19.5 & 20.7 & 39.1 & 5.1 & 4.0 & 7.8 \\ C-PPP & 52.7 & 35.1 & 59.4 & 5.8 & 4.4 & 9.0 \\ GR-PPP & 18.4 & 9.4 & 17.3 & 2.6 & 2.3 & 4.5 \\ GE-PPP & 11.9 & 8.4 & 17.6 & 2.0 & 1.8 & 4.0 \\ GC-PPP & 14.3 & 10.0 & 16.1 & 2.3 & 1.8 & 4.3 \\ GREC-PPP & 11.5 & 6.9 & 13.0 & 1.7 & 1.6 & 3.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 16: Kinematic positioning accuracy and convergence time of real-time PPP (long-term performance of PPP based on daily observations) with CNES products for different system combinations using the datasets from 29 stations spanning a week. Besides, we characterize the consistency of precise satellite products from different analysis centers. It should be noted that all the following numbers are only valid for the long-term performance of PPP based on daily observations. Based on the SISRE values, the consistency among the ESA, GFZ and WHU precise products is usually better than 1.5, 3.0, 2.5, 4.5, 4.0, 22.5, 10.5, 32.5 and 15.5 cm for the GPS, GLONASS, Galileo, BDS-2 MEO, BDS-3 MEO, BDS-2 GEO, BDS-2 IGSO, QZSS GEO and QZSS IGSO satellites (except for the WHU products for GPS and GLONASS satellites), respectively. As for the consistency between the CNES real-time products and the three post-processed precise products, the SISRE values are increased, and the corresponding statistic is usually smaller than 3.0, 6.0, 5.5, 5.5, 7.5, 55.5 and 9.5 cm for the GPS, GLONASS, Galileo, BDS-2 MEO, BDS-3 MEO, BDS-2 GEO and BDS-2 IGSO satellites, respectively. In addition, the consistency of precise products in eclipsing seasons is usually worse than that outside eclipsing seasons. The post-processed GRECJ-PPP can provide a convergence time of 5.9-6.9/2.6-3.1/6.3-7.1 min and a positioning accuracy of 0.2-0.3/0.2-0.3/1.0-1.1 cm in the static mode in the east/north/up directions, respectively, while the corresponding statistics are 6.8-8.6/3.3-4.0/7.8-8.1 min and 1.0-1.1/0.8/2.5-2.6 cm in the kinematic mode in the three directions, respectively. A static convergence time of 8.7/5.2/11.2 min, a static positioning accuracy of 0.6/0.8/1.3 cm, a kinematic convergence time of 11.5/6.9/13.0 min, and a kinematic positioning accuracy of 1.7/1.6/3.6 cm in the three directions can be achieved for the real-time GREC-PPP, respectively. The static positioning accuracy of post-processed PPP does not exhibit significant difference for different system combination cases, which is smaller than 0.4/0.2/0.5 cm in the three directions, respectively, and the static positioning accuracy of post-processed GRECJ-PPP with WHU, GFZ and ESA precise products is comparable to each other.