## 2 Data Quality Characteristic Analysis
### Satellite Visibility  
Figure 2 provides a comparison of the number of visible satellites in each constellation and frequency as observed using the HP40 and Mi11 GNSS receivers. Specifically, \"B1C&B2a\" indicates the satellites observed using smartphones with BIC and B2a signals, and \"B1C&B2a&B1I\" includes the satellites observed with BIC, B2a, and B1I data. Similarly, \"L1&L5\" and \"E1&E5a\" follow the same conventions as described above.  
Figure 2 clearly shows that the number of visible GPS L5 satellites was consistently lower than four for the HP40. By contrast, Mi11 observed more than four GPS L5 satellites only in the static open-sky scenario. In all other scenarios, except for the static open-sky scenario, Mi11 observed fewer than four satellites for most of the observation epochs.  
Figure 1: Information on dataset collection. (**a**) Static dataset collection environment and relative positions of smartphones and geodetic receiver. (**b**) Trajectory of dynamic dataset collections and relative positions of two smartphones and geodetic receiver.  
Figure 2: Number of visible satellites for smartphone multi-GNSS. (**a**) Number of satellites for HP40 and Mi11 in the static open-sky scenario; (**b**) number of satellites for HP40 and Mi11 in the static complex scenario; (**c**) number of satellites for HP40 and Mi11 in the dynamic typical urban scenario; (**d**) number of satellites for HP40 and Mi11 in the dynamic complex urban scenario.  
In the static open-sky scenario, HP40 observed approximately seven to eight BDS-3 B1C satellites, seven to ten B2a satellites, nine to eleven B1I satellites, six to seven satellites for B1C&B2a, and six to seven satellites for B1C&B2a&B1I. On the other hand, Mi11 recorded eight to eleven satellites for B1C, B2a, B1C&B2a, and B1C&B2a&B1I, and ten to fifteen satellites for B1I. It is worth noting that in two epochs, Mi11 did not detect any B1I or B1C&B2a&B1I satellites. For GPS, the HP40 typically observed five to eight L1 satellites, one to two L5 satellites, and one to two L1&L5 satellites. By contrast, Mi11 observed six to ten L1 satellites and three to seven L5 satellites. Regarding Galileo, HP40 typically observed five to seven E1 satellites and six to eleven E5a satellites. Meanwhile, Mi11 observed six to eleven Galileo satellites. Table 1 presents the average number of visible satellites across various frequencies for both HP40 and Mi11 in the static open-sky scenario. Figure 2 and Table 1 clearly indicate that HP40's performance in decoding satellite data was inferior when compared to Mi11. This difference in performance could be attributed to the fact that Mi11, equipped with a new-generation chip, was released in March 2021, by which time the BDS-3 system had already been operating successfully. Notably, the Mi11 has the capability to obtain C59 and C60 B1I observations, which HP40 cannot access.  
In the static complex scenario, when compared to the static open-sky scenario, HP40 consistently maintained the same number of visible satellites for BDS-3, GPS, and Galileo. However, Mi11 experienced a decrease of one to two satellites. It is worth noting that the fluctuation range of the number of visible satellites for each constellation is greater than that in the static open-sky scenario. In the dynamic scenario, HP40 witnessed a reduction of one satellite for BDS-3, GPS, and Galileo compared to the static open-sky scenario, whereas Mi11 experienced a more substantial decrease of two to three satellites. Notably, the fluctuation range of the number of visible satellites for each constellation remained the same as in the static open-sky scenario for HP40, but it was larger than that in the static open-sky scenario and smaller than that in the static complex scenario for Mi11. This suggests that Mi11's performance in tracking satellites may be weaker compared to HP40 in certain scenarios.