*3.3. Triple-Frequency PPP Positioning Performance Analysis* 3.3.1. Static Mode

First, the static results of the ASCG station for 2022 DOY 65, from 00:00 UTC to 4:00 UTC, were compared for 1 of the 21 stations. The static PPP positioning error curves under the two solutions of the GPS, BDS-3, and Galileo are shown in Figure 5. During this period, the number of triple-frequency satellites for the ASCG stations of GPS, BDS-3, and Galileo systems was 4.8, 7.6, and 6.6, respectively, indicating that the triple-frequency satellites were involved in the triple-frequency PPP solution.

From Figure 5, it can be observed that the GPS positioning accuracy for the ASCG station was more stable after correcting the IFCB. Meanwhile, for the BDS-3 and Galileo, the change in single-day positioning accuracy was less than 0.1 mm after the IFCB correction, i.e., the positioning accuracy was basically unchanged, which further verifies that the influence of IFCB on the positioning of the BDS-3 and Galileo can simply be ignored. Furthermore, to further analyze the impact of IFCB on GPS positioning, the static PPP accuracy and convergence time under the two scenarios of the GPS at 21 stations for 7 days were recorded, as shown in Table 3. Without correcting the IFCB, the E, N, U, and 3D positioning accuracy of the GPS system was 1.56 cm, 0.6 cm, 1.69 cm, and 2.38 cm, respectively. On the other hand, following the IFCB correction, the positioning accuracy of the GPS improved to 0.99 cm, 0.48 cm, 1.34 cm, and 1.73 cm, respectively, among which the 3D positioning accuracy was improved by 27.39%. The convergence times for the GPS with corrected and uncorrected IFCB were 21.64 min and 24.19 min, respectively, illustrating a 10.55% improvement in the convergence time. It can be clearly seen that IFCB had a serious impact on the GPS static positioning, and the multi-frequency PPP performance of the GPS was improved by adding the IFCB.

**Figure 5.** ASCG station static mode PPP positioning error curve (DOY 65, 2022; UTC: 00:00 to 4:00).



#### 3.3.2. Imitation Kinetic Mode

Regarding the kinematic mode, the results of the ASCG measurement station for 2022 DOY 65 are compared as an example. The positioning error curves under the two schemes of GPS, BDS-3, and Galileo satellites are plotted in Figure 6. During this period, the number of triple-frequency satellites in the GPS, BDS-3, and Galileo systems was 5.2, 7.6, and 6.5, respectively.

As evident from Figure 6, the kinematic and static modes followed a similar pattern, and likewise, the positioning accuracy of the ASCG station GPS was more stable after the IFCB correction, while for the BDS-3 and Galileo, the single-day 3D positioning accuracy was improved from 6.21 cm and 6.30 cm to 6.20 cm and 6.29 cm, respectively, and the change in positioning accuracy was less than 0.1 mm. The statistics related to PPP positioning

accuracy and convergence time in the kinematic mode under the two solutions of the GPS at 21 stations for 7 days are provided in Table 4. Without correcting the IFCB, the E, N, U, and 3D positioning accuracy of the GPS was 2.59 cm, 1.77 cm, 4.81 cm, and 5.74 cm, respectively, whereas after the IFCB correction, the GPS positioning accuracy was enhanced to 2 cm, 1.43 cm, 4.06 cm, and 4.75 cm, respectively, where the 3D positioning accuracy was improved by 17.34%. Furthermore, the convergence times for the GPS with corrected and uncorrected IFCB were 21.64 min and 24.19 min, respectively, indicating a 15.22% improvement. Similar to the static mode, the impact of IFCB on the multi-frequency precise point positioning in the GPS kinematic mode was also significant, and the multi-frequency precise point positioning performance of the GPS was further improved by the addition of IFCB.

**Figure 6.** ASCG station kinematic mode PPP positioning error curve (DOY 65, 2022; UTC: 00:00 to 24:00).

**Table 4.** Statistics of PPP positioning accuracy and convergence time under 7-day GPS kinematic mode for 21 stations (RMS, unit: cm; convergence time, unit: min).

