## 5 GNSS Positioning Performance of Xiaomi Mi 8
### Dynamic Test Analysis  
Figure 16 shows the trajectories of the time differenced filter kinematic solutions with respect to a combination of different systems and frequencies. Tables 5 and 6 give the statistical information of the navigation results under open-sky (track 1) and GNSS-degraded environments (track 2), respectively. For the mass-market navigation, the accuracy and availability of the navigation in the horizontal direction are usually more concerned. Here, the definition of the solution availability is made with a 5 m 2D accuracy criterion, instead of 20 m 3D accuracy in the static case. In addition, the average number of pseudorange observations in each solution is also given. As illustrated in Figure 16 and Table 5 for track 1, with the increase of observations, the navigation performance of the time differenced filter is significantly improved, and the trajectories become very smooth. For the single-frequency case, continuous and smooth navigation results are obtained by only using GE satellites. Compared with the GPS-only solution, when using GEJC observations, the average number of used satellites increased to 14.2. The availability of navigation results increased from 62.1% to 92.9%, and the RMS of horizontal position errors decreased from 4.05 m to 1.48 m. When L5/E5 \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Frequency-GNSS** & **E (m)** & **N (m)** & **U (m)** \\ \hline SF-GEJC & 0.830 & 1.973 & 4.115 \\ DF-GEJC & 0.713 & 1.442 & 2.156 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: RMS of TD filter solutions for Xiaomi Mi 8 in GNSS-degraded environment (track 2). Figure 16: Trajectory of the kinematic solutions of different systems and frequencies. The blue rectangles indicate the area where the GNSS signals are severely degraded due to the tall buildings. observations are available, the navigation performance is further improved, and the overall navigation trajectory is smoother than that of only using single-frequency observations. Here, even when only GE observations are used, the solution availability reaches 92.7%, which is nearly equivalent to that of single-frequency results with GEJC observations, and the RMS of horizontal position errors decreases to 1.68 m. In addition, when using dual-frequency GNSS observations of GREC satellites, the navigation availability is 97.8%. Correspondingly, the average number of used observations increases to 22.1, and RMS of the horizontal position errors is about 1.22 m.  
The navigation results in the adverse GNSS environments of track 2 are given in Figure 16 and Table 6. Clearly, due to the unfavorable navigation environment, the navigation performance of Xiaomi Mi 8 rapidly deteriorates, and navigation trajectory jitters occur. For instance, even with the use of GEJC observations, the single-frequency navigation solutions still present obvious jitters, especially in areas with severe signal occlusion (between tall buildings and dense trees, the southern blue block in the Figure 16). The RMSs of position errors in the E, N, and U directions are 0.830 m, 1.973 m, and 4.115 m, respectively. The situation is obviously improved, when dual-frequency GNSS observations are used, as shown in the bottom four panels of Figure 16. It is seen that continuous and accurate navigation results are achieved even in the southern area where GNSS signals are severely degraded due to the tall buildings. The navigation accuracy is improved with the position RMSs in the E, N, and U directions reduced to 0.713 m, 1.442 m, and 2.156 m, respectively. From the above analyses, it can be found that using multi-GNSS observations can effectively improve the accuracy and availability of mobile phone navigation. What is more important, the newly added second frequency L5/E5 observations, with their excellent observation accuracy, provide better location services in terms of navigation availability and positioning accuracy even in adverse GNSS environments.