## 3 Experiments and Discussions
### Accuracy and Convergence of RT-PPP in MGEX Stations
#### 3.3.2 Single-Frequency PPP  
In this section, a single-frequency PPP model with ionospheric and receiver DCB constraints is used. The time series of position differences between the static single-frequency PPP and the reference results in the E, N, and U for each station are shown in Figure 9, and the corresponding statistics are presented in Figure 10. The positioning accuracy in terms of RMSE of BDS BIC PPP with PPP-B2b SSR products is better than 5.5 cm in the E, N, and U for each station. While using GPS L1, the PPP accuracy is better than 5.6 cm in three components. The positioning accuracy of single-frequency PPP with PPP-B2b is comparable to that of IGS real-time RTS products, which have similar performance to the dual-frequency PPP. The positioning accuracy of static single-frequency PPP using WHU ultra-rapid product and broadcast ephemeris is much lower than that with PPP-B2b. The maximum positioning error for broadcast ephemeris-based solution exceeds 39.5 cm in the three components.  
According to the statistics of average positioning error in Table 6, single-frequency RT-PPP based on PPP-B2b SSR products and IGS RTS SSR products (except DLR) can satisfy the demand for centimeter-level high-precision real-time positioning accuracy. While using PPP-B2b SSR products, the position accuracies in horizontal and 3D of BIC PPP are 5.4 cm and 7.7 cm, respectively. While using the IGS RTS products, the BIC PPP based on WHU products provides the highest accuracy within 3.5 cm in horizontal, and the PPP based on GFZ products provides the highest accuracy in 3D with 7.0 cm among evaluated the IGS RTS products. In contrast, the DLR real-time products provide the worst static BIC PPP positioning accuracy with 5.5 cm and 14.3 cm in the horizontal and 3D. The horizontal/3D positioning accuracies using WHU ultra-rapid products and broadcast ephemeris were about 7.6/13.1 cm and 18.3/43.5 cm, respectively, much lower than those of PPP-B2b PPP. As a comparison, the positioning accuracies of GPS L1 PPP based on PPP B2b SSR products are 5.4 cm and 7.8 cm, similar to those of BDS-3 BIC PPP.  
To present the convergence speed of single-frequency BIC PPP, we redefine the convergence criteria of static PPP to be that the position accuracies in horizontal and vertical are continuously better than 20 cm and 40 cm for at least 10 min. The convergence times of static single-frequency PPP based on different SSR products for each MGEX station are shown in Figure 11, in which the average convergence times of BDS-3 BIC PPP and GPS L1 PPP using PPP-B2b SSR products are 80 min and 73 min, respectively. For solutions  
Figure 8: Convergence time of static dual-frequency PPP using different real-time orbit and clock products.  
based on the four IGS real-time products, the converge times with CAS's products are the shortest among other products, with an average time of 65 min. The DLR products-based solutions converge the slowest with an average time of 95 min.  
Figure 10: Average accuracy of the four-day single-frequency static PPP.  
Figure 9: Time series of position errors of the four-day single-frequency static PPP.