# Real-Time Geophysical Applications with Android GNSS Raw Measurements
## 3 Results
### Periodic Dynamic Scenario  
The outcomes from the test in the static scenario encouraged the use of a vibrating table in order to expose the smartphone to a periodic movement (Figure 3). On 2 April 2019 the Xiaomi Mi 8 and a geodetic class receiver (STONEX S900A) were fixed over a table placed in an open-sky environment in order to reduce multipath, interferences, and cycle slip for 10 min. The table subjected the two GNSS receivers to a 1D periodic motion with an oscillation period of about 10 s and an amplitude of 0.125 cm. Unfortunately, due to the mechanical characteristics of the table, the motion was irregular but this was negligible for the purpose of this paper. If the acquisition rate for the Xiaomi Mi 8 was fixed at 1 Hz from the Android Raw GNSS Measurements API, 10 Hz observations were collected by the STONEX S900A. However, the reference solution enabling the performance evaluation of the Xiaomi Mi 8 was built on 1 Hz measurements derived from the STONEX S900A. The table alternated between static and kinematic conditions during the tests. Although the low resistance of the GNSS antenna embedded in the smartphone to the multipath phenomenon is a well-known problem, its effect on carrier-phase observations (the only one used from the algorithms discussed in this paper) is lower compared to pseudorange measurements. Nevertheless, a preliminary analysis of the GNSS observables was carried out in order to detect possible environmental factors affecting the measurements. The Android Raw GNSS Measurements API allows the decoding of carrier-to-noise density ratio (C/No) measurements, defined as the ratio of the carrier power (C) to the noise power density (No), expressed in dB-Hz. Even if the C/No values depends on the GNSS equipment used, the careful analysis of its behavior may indicate environmental interference on the signal. Figure 4 shows the traditional dependency between elevation and C/No in high-end receivers. The same dependency is not always clear with Android GNSS measurements, where the C/No is noisier and less stable (Figure 5). As expected, the measurements from the Xiaomi were characterized by lower C/No: the reduction, with a maximum value of 19 dB-Hz, was independent of the azimuth but higher differences were observed for the satellites with higher elevation (Table 2). The skyplots analysis confirms the independence of the C/No values from the azimuth for both the receivers (Figure 6). The results are in line with published research in this field [5; 7; 8]. \begin{table}
\begin{tabular}{l c c c} \hline \hline  & \multicolumn{3}{c}{**RMSE (m/s)**} \\ \hline  & **East** & **North** & **Up** \\ \hline
**Xiaomi Mi 8** & 0.003 & 0.007 & 0.012 \\
**MOSE** & 0.001 & 0.001 & 0.002 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Root mean square errors (RMSEs) for VADASE solutions with the two different GNSS receivers. Figure 3: Vibrating table used to perform the tests. Due to the short acquisition time-typical of GNSS applications for smartphones, no further multipath analysis could be carried out. However, the impact of multipath for the kinematic application studied in this paper can be considered small given the satisfactory C/No values for the signals acquired. Moving on the VADASE solutions, Figure 7 illustrates the time series of the 3D velocity estimated for all the epochs in the analysis. Static and kinematic periods were clearly identified from both the receivers and acquisition rate--for the STONEX S900A--used in this test.