## 3 Results
### Performance of Multi-System PPP with Precise Products from Different Analysis Centers
#### 3.4.2 Static Position Solutions
By introducing GPS observations, with the use of WHU, GFZ and ESA products, we can achieve a convergence time improvement of 82-85%/85-90%/84-88% for GR-PPP over R-PPP, of 18-39%/53-63%/57-63% for GE-PPP over E-PPP, and of 54-68%/65-71%/59-67% for GC-PPP over C-PPP over C-PPP, as well as an accuracy improvement of 65-73%/65-70%/54-55% for GR-PPP over R-PPP, of 66-72%/57-75%/48-54% for GE-PPP over E-PPP, and of 59-68%/52-61%/49-52% for GC-PPP over C-PPP in the east/north/up directions, respectively. In contrast to G-PPP, GJ-PPP slightly shortens the convergence time (less than 10%), but the improvement on the positioning accuracy is relatively obvious (15-20%/14-18%/12-16% in the three directions). Compared with G-PPP, GRECJ-PPP reduces the convergence time by 72%/73%/69%, 67%/74%/69%, and 59%/73%/60% to 8.6/3.8/8.0, 8.0/4.0/8.1, and  
When using the precise products from different ACs, several combination cases exhibit distinct positioning performance. G-PPP with WHU products obtains slightly worse positioning accuracy in the east direction (an accuracy degradation of 7-9 mm) than that with GFZ and ESA products, and it is also the case for GJ-PPP. The positioning accuracy of E-PPP with WHU products is improved by about 1 cm compared with that with GFZ and ESA products in all three directions. As to other combination cases, the accuracy difference is usually confined to 0.5 cm. The differences of convergence time between the post-processed PPP with GFZ and ESA products are smaller than 3 min for all combination cases, except for G-PPP, R-PPP and GJ-PPP cases. The convergence time difference is also less than 3 min for C-PPP, GR-PPP and GRECJ-PPP with the precise products from different ACs. When using ESA products, G-PPP, GJ-PPP and GC-PPP achieve the shortest convergence time in comparison with those with WHU and GFZ products. Both E-PPP and GE-PPP cases with WHU products have the longest convergence time than those with GFZ and ESA products. The difference of convergence time can be up to about 10 min for R-PPP with WHU, GFZ and ESA products in all three directions. Compared with the static post-processed PPP results shown in Tables 9-11, both the positioning errors and convergence time of the corresponding kinematic ones are increased by a factor of 3.5 times on average. Figure 13 illustrates the epoch-wise position errors of kinematic PPP for the four single-system cases and GREC-PPP at the station KIR0 on 17 May 2020 using CNES real-time precise products. It can be seen that the real-time kinematic positioning performance of the single-system cases is much inferior to GREC-PPP, especially for C-PPP, E-PPP and R-PPP. The epoch-wise position errors of the single-system cases vary within 8, 8 and 10 cm in \begin{table}
\begin{tabular}{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{2-6}  & **East** & **North** & **Up** & **East** & **North** & **Up** \\ \hline G-PPP & 16.6 & 12.2 & 19.7 & 2.5 & 2.1 & 4.3 \\ R-PPP & 63.5 & 48.0 & 82.3 & 5.0 & 3.7 & 7.1 \\ E-PPP & 15.4 & 14.5 & 32.0 & 4.1 & 2.8 & 6.1 \\ C-PPP & 29.9 & 20.2 & 32.8 & 2.8 & 2.2 & 5.3 \\ GR-PPP & 9.8 & 5.0 & 9.9 & 1.4 & 1.1 & 3.3 \\ GE-PPP & 9.4 & 5.3 & 12.1 & 1.2 & 1.0 & 3.1 \\ GC-PPP & 9.6 & 5.8 & 10.8 & 0.9 & 0.9 & 2.7 \\ GJ-PPP & 16.1 & 12.9 & 19.2 & 2.0 & 1.8 & 3.8 \\ GRECJ-PPP & 6.8 & 3.3 & 7.8 & 1.1 & 0.8 & 2.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 15: Kinematic positioning accuracy and convergence time of post-processed PPP (long-term performance of PPP based on daily observations) wlth ESA products for different system combinations using the datasets from 29 stations spanning a week.