## 6 Conclusions and Outlook  
In this paper, we comprehensively analyzed the characteristics of raw GNSS observations from Xiaomi Mi 8, and conducted positioning experiments under open-static and dynamic GNSS-degraded environments. Firstly, we found that the C/N0 of the smart device is about 4 to 11 dBHz lower than those of geodetic receivers, and characterized by rapid variations. In addition, C/N0 are not significantly correlated to the satellite elevations. Secondly, we investigated the pseudorange and carrier phase observation error characteristics of Xiaomi Mi 8. The results show that the pseudorange noise of the L1/E1 observations is as high as 3-9 m in complex dynamic environments while that of L5/E5 observations is about 1.5 m. The correlation between the pseudorange noise and C/N0 is obvious, and a C/N0-dependent weight model is used for Xiaomi Mi 8 GNSS positioning. At the same time, we found that the pseudorange noise of Xiaomi Mi 8 is so large that the pseudorange ionosphere-free combination model is not suitable for Xiaomi Mi 8 GNSS positioning. As to the carrier phase observations, the observation noise is about 2 cm, but the cycle slip percentages of carrier phase observations are quite high in dynamic tests, rising to 62.25% in GNSS-degraded environments. Therefore, in order to effectively utilize the high precision carrier phase observations, a time differenced positioning filter is proposed to deliver continuous and smooth navigation results in urban GNSS-degraded environments. Figure 17: PDOP, the IEPV status, the number of observations collected, and the number of observations used in the positioning solution. (**a,b**) represent the status of kinematic solutions with GEJC systems and single frequency observations in the open and GNSS-degraded environments, respectively. Correspondingly, (**c,d**) give the status with GEJC systems and dual-frequency observations in track 1 and track 2. The red line is the number of the used observations. The blue line is the number of the viewed observations. The green line is the PDOP. The black line is the IEPV status. Finally, the single-device positioning performance of Xiaomi Mi 8 using a time differenced filter was investigated, especially the positioning performance improvement with the inclusion of L5/E5 observations in GNSS-degraded environments. The RMSs of the horizontal and vertical position errors can be as small as 1.0 m and 1.5 m, respectively, using multi-system dual-frequency GNSS observations under static conditions. In the dynamic open environment, the average number of used observations was about 22.1, the RMS of horizontal errors was about 1.22 m, and the navigation availability reached 97.8%. Correspondingly, under the adverse GNSS environments, the horizontal navigation accuracy was about 1.61 m when L5/E5 observations were available. Clearly, this TD filter algorithm can deliver satisfied positioning results for various LBSs. It can also be expanded to newly emerged applications, like augmented reality, seamless image-based navigation, and photogrammetric data collection applications in complex environments. The L5/E5 signal from Xiaomi Mi 8 has outstanding characteristics, and provides better location services in terms of positioning availability and accuracy even in GNSS-degraded environments. Nevertheless, due to the vulnerability of the GNSS signal, work on multi-sensor fusion (such as GNSS/MEMS fusion) for the pedestrian navigation is underway to ensure continuous navigation in a GNSS signal denied environment. Conceptualization, L.G. and F.W. ; methodology, L.G. and F.W. ; software, F.W., L.G., and X.G. ; validation, L.G. and X.L. ; formal analysis, F.W. ; resources, F.W. ; data curation, L.G. ; writing--original draft preparation, L.G. ; writing--review and editing, X.G., X.L. and J.S. ; visualization, L.G. and X.L. ; supervision, J.S. and W.Z. ; project administration, F.W. ; funding acquisition, F.W. All authors have read and agreed to the published version of the manuscript.