# A Combined Elevation Angle and C/N0 Weighting Method for GNSS PPP on Xiaomi MI8 Smartphones
## 4 Experimental Results and Discussion
### Kinematic Experiment in Constrained Visibility Environment  
A kinematic GNSS experiment was conducted using the Xiaomi MI8 smartphone in a constrained satellite visibility environment on 12 October 2021, on the new campus of Central South University, China. The satellite visibility is easily affected by the buildings and trees along its trajectory, as shown in Figure 11. The equipment setup is similar to the previous experiment shown in Figure 5. The experiment equipment was carried by an electric bicycle. The entire data collection lasts about half an hour with a sampling rate of 1 HZ. The elevation mask is set to 10 degrees.  
Figure 12 shows the total number of satellites received, total number of satellites used and the number of satellites for different constellations of GPS, GLONASS, BDS and Galileo in the PPP. Similar to the previous experiment, the number of GPS and BDS satellites observed is more than the GLONASS and Galileo satellites. The total number of satellites received for the Trimble NetR9 receiver is less than that in the open area at an average of about six satellites due to the constrained satellite visibility environment. In contrast, the number of satellites used on the Xiaomi MI8 smartphone in the constrained environment is larger than that in the open area by an average of about two satellites, which indicates that the number of GNSS satellites observed on smartphones is unstable in different sessions. Furthermore, due to the observation environment influence, the number of satellites used in PPP significantly fluctuates.  
\begin{table}
\begin{tabular}{c c c c} \hline  & **ELE** & **C/N0** & **ELE/CN0** \\ \hline East (m) & 0.74 & 1.19 & 0.55 \\ North (m) & 0.75 & 0.77 & 0.73 \\ Up (m) & 1.83 & 1.62 & 1.35 \\
3D (m) & 2.11 & 2.15 & 1.63 \\ \hline \end{tabular}
\end{table}
Table 2: RMS Statistics of the PPP errors in the east, north and up directions.  
Figure 11: Kinematic experimental trajectory in a constrained satellite visibility environment.  
Figure 13 shows the observation variances derived from Equations (5), (6) and (8) for the GPS G06 at the L5 frequency and the GLONASS R04 at the G1 frequency. The observation variances are displayed in the top, middle and bottom panels, derived from three different weighting scenarios, namely elevation-angle-only, C/N0-only and combined elevation angle and C/N0. Similar to the previous experiment, the C/N0-derived observation variances severely vary, while the observation variances derived from the combined elevation angle and C/N0 weighting scenarios are more stable.  
Figure 14 shows the positioning errors in the east, north and up components using the three weighting scenarios. It can be seen that the positioning error curves derived from the combined weighting scenario is much closer to the zero axis, especially in the north and up directions. The RMS statistics of the positioning errors are provided in Table 3. Based on the combined weighting scenario, the RMS values of the PPP errors are 1.00 m, 0.62 m and 2.22 m in the east, north and up components, respectively, which improve by about 19.3%, 12.7% and 55.9% over the elevation-angle-only weighting scenario in the east, north and up directions, respectively and by about 51.6% and 26.7% over the C/N0-only weighting scenario in the north and up components, respectively. For the 3D position, the corresponding improvement can reach 52.0% and 26.0%, respectively. In addition, it is  
Figure 12: Number of satellites for quad-constellation GNSS on 12 October 2021.  
Figure 13: Carrier phase observation variances for GPS G06 satellite at L5 frequency (**a**) and GLONASS R04 satellite at G1 frequency (**b**).  
more prone to reconvergence under the constrained satellite visibility condition, which is especially apparent in the up direction. The achieved PPP accuracy is comparable to the existing research [12; 13].