## 2 Data Quality Characteristic Analysis
### Signal Power  
The CNR represents the ratio of signal power to noise in the process of receiving the signal. The CNR value serves as an indicator of the signal noise level of observation satellites during experimental measurements. A lower CNR value indicates poorer observation quality. Table 2 presents the average CNR values in dB-Hz for each frequency of both HP40 and Mi11 in the static open-sky scenario. Figure 3 illustrates a comparison of the CNR for each frequency in smartphone GNSS observations. In general, the CNR for multi-GNSS signals fell within the range of 25-45 dB-Hz. Specifically, for HP40, the CNR of the B2a/L5/E5a signal was approximately 10 dB-Hz lower than that of B1C/B1I/L1/E1, whereas for Mi11, it was approximately 6 dB-Hz lower. In the static complex scenario, the CNR was 4 dB-Hz lower than in the static open-sky scenario for HP40 and 2 dB-Hz lower for Mi11. In the dynamic typical urban scenario, both HP40 and Mi11 exhibited a CNR approximately 2 dB-Hz lower than in the static open-sky scenario. Additionally, in the dynamic complex urban scenario, the CNR was approximately 2 dB-Hz lower than in the dynamic typical urban scenario. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Device** & **B1C** & **B2a** & **B1I** & **B1C\&B2a** & **B1C\&B2a\&B1I** & **L1** & **L5** & **L1\&L5** & **E1** & **E5a** & **E1\&E5a** \\ \hline HP40 & 7 & 8 & 9 & 6 & 6 & 6 & 1 & 1 & 5 & 5 & 5 \\ Mi11 & 9 & 10 & 12 & 9 & 9 & 8 & 5 & 5 & 8 & 8 & 8 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Average numbers of satellites in each frequency for smartphones in the static open-sky scenario. As seen in Figure 3, in the static open-sky scenario, the proportion of satellites with a CNR below 25 dB-Hz was very small. Specifically, for Mi11, 40-70% of the BDS-3 B1C/B1I and GPS L1 satellites had a CNR exceeding 40 dB-Hz, while the percentages for HP40 were 39-65%. Approximately 25% of Galileo E1 satellites had a CNR exceeding 40 dB-Hz. Regarding the second-frequency signals, for Mi11, only approximately 8% of GPS L5 satellites had a CNR exceeding 40 dB-Hz, and the majority of them were around 36 dB-Hz. Additionally, less than 1% of BDS-3 B2a satellites had a CNR exceeding 40 dB-Hz, with most of them around 33 dB-Hz. As for Mi11's E5a CNR, it was mainly distributed around 32 dB-Hz. However, for HP40, there were no second-frequency satellites with CNRs exceeding 40 dB-Hz. For HP40, the CNR value for B2a was mainly distributed around 29 dB-Hz, while it was around 31 dB-Hz for L5 and around 25 dB-Hz for E5a. However, in the static complex and dynamic scenarios, the CNR decreased due to interference from the surrounding environment. When the CNR of smartphone GNSS observations drops below 25 dB-Hz, it can significantly increase the occurrence of gross errors. In such cases, if there is a sufficient number of visible satellites, it is crucial to take measures to avoid using observations with CNRs below 25 dB-Hz, so as to minimize abnormal positioning results. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Device** & **B1C** & **B2a** & **B1I** & **L1** & **L5** & **E1** & **E5a** \\ \hline HP40 & 38.32 & 27.54 & 39.77 & 40.04 & 32.01 & 35.70 & 25.33 \\ Mi11 & 41.06 & 33.64 & 39.59 & 39.07 & 35.90 & 35.84 & 32.50 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The average CNR values in each frequency for smartphones in the static open-sky scenario. Figure 3: Distribution of the CNR for smartphones’ multi-GNSS. (**a**) CNR distribution for HP40 and Mi11 in the static open-sky scenario. (**b**) CNR distribution for HP40 and Mi11 in the static complex scenario. (**c**) CNR distribution for HP40 and Mi11 in the dynamic typical urban scenario. (**d**) CNR distribution for HP40 and Mi11 in the dynamic complex urban scenario. Figure 4 illustrates that as elevation increased, there was no significant increase in the CNR. Therefore, the relationship between the CNR and elevation does not appear to be closely correlated.