## 5 GNSS Positioning Performance of Xiaomi Mi 8
### Static Test Analysis  
In order to analyze the achievable positioning performance by multi-system and dual-frequency observations, especially the newly added L5/E5 frequency in Xiaomi Mi 8, the GNSS observations were processed by SPP and the time differenced filter for the cases of GPS-only (G), GPS/Galileo (GE), GPS/Galileo/QZSS (GEJ), and GPS/Galileo/QZSS/BeiDou (GEJC) with single-frequency and dual-frequency observations. The results are illustrated in Figures 14 and 15. The horizontal position error scatters are shown in the odd columns while the vertical error scatters are shown in the even columns. The ellipses or straight lines inside each panel denote the 2\(\sigma\) domain of the scatters (95% confidence level). The smaller the ellipse is, the smaller the standard deviation, and the smoother the result. A comparison of the RMSs of the positioning errors is shown in Table 4. We also calculated the solution availability, which is the percentage of solved positions that have a 3D error less than 20 m. Meanwhile, considering the advantage of the Galileo system and those GPS satellites with L5, we also conducted a positioning experiment using the Galileo and those GPS satellites with L5 measurements, labeled as 'GE(L1+L5)'. Although, Figure 11 indicates that the ionosphere-free combination pseudorange may not be suitable for GNSS positioning with raw data from Xiaomi Mi 8 for its extreme large combined noise. Here we still conducted positing experiments with the \begin{table}
\begin{tabular}{l l} \hline \hline \multicolumn{1}{c}{**Setting Items**} & \multicolumn{1}{c}{**Details**} \\ \hline Observations used &
\begin{tabular}{l} Uncombined L1/E1 and L5/E5 pseudorange and carrier \\ phase measurements \\ \end{tabular} \\ \hline GNSS orbit and clock & Broadcast ephemeris (F/NAV messages for Galileo) \\ \hline Parameters to be estimated & Position, clock offsets \\ \hline Weighting model & (1) & C/N0-dependent weighting signal-in-space range error (SISRE) value-based weighting \\ \hline Ionospheric delay & Ionospheric delay correction model of each GNSS system \\ \hline Tropospheric delay & Saastamoinen model \\ \hline Satellite cutoff elevation & 10\({}^{\circ}\) \\ \hline Parameter estimation method & Time differenced filter \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The detailed positioning strategies. dual-frequency ionosphere-free combined GPS, Galileo, and QZSS measurements to verify this, labeled as 'GEJ(IONO-FREE)'. Figure 14: Positioning errors of single frequency time differenced (TD) filter and SPP solutions for Xiaomi Mi 8 with L1/E1 measurements in open-sky rooftop situations. The horizontal position scatters are shown in the odd columns, while the vertical scatters are shown in the even columns. The concentric ellipses or straight lines inside each panel denote the \(2\sigma\) domain of the scatters. Figure 15: Cont. It can be found that, for single-frequency SPP results, when the used navigation systems are increased, the RMS of the horizontal position errors decreases from 6 to 4 m, and 9 to 7 m for that of the vertical position errors. When using dual-frequency GNSS observations, the accuracy of SPP solutions improves slightly. The horizontal error RMS can be as good as 3.5 m, while the vertical error RMS is about 6.5 m. The increase in used navigation systems and inclusion of the second frequency have no obvious effect on the improvement of single-frequency SPP positioning accuracy, but the solution availability gets an effective boost. In the case of the single-frequency GEJC GNSS, the maximum solution availability can reach 98%. For dual-frequency GNSS cases, the positioning availability can be more than 99% when GPS and Galileo observations are used, and higher with the use of more systems. In short, the static data processing shows that, although the use of dual-frequency observations only has a slight improvement in the SPP accuracy, it strongly enhances the SPP solution availability.