## 3 Results
### Preliminary Data Analysis: Measurement Availability, Signal Strength, and Geometry
The mean \(C/N_{0}\) values are 39.8 dB-Hz for uBlox and 31.5 dB-Hz for Xiaomi. Such behavior is, as previously mentioned, related to differences in antenna and receiver architecture between the considered devices. Similar behaviors are also evident for Galileo in panels (f) and (g); in this case, the mean \(C/N_{0}\) value is 40.2 dB-Hz for uBlox and 30.4 dB-Hz for Xiaomi. Even for BeiDou, it is evident that for Xiaomi, panel (h), lower \(C/N_{0}\) values are present in comparison to uBlox, panel (i); the mean \(C/N_{0}\) values are 36.6 dB-Hz for uBlox and 30.2 dB-Hz for Xiaomi. In Table 1, the mean, maximum, and minimum \(C/N_{0}\) values for each GNSS and for each device are summarized. It is evident that for each GNSS, the higher the device grade, the higher the mean \(C/N_{0}\) value. GPS measurements have, on average, larger \(C/N_{0}\) values in comparison to the measurements from the other systems. Glonass and Galileo measurements, fixed the device, have similar mean \(C/N_{0}\) values, while the lowest values are found for BeiDou. The low mean values of \(C/N_{0}\) for BeiDou are due to the presence of GEO and IGSO satellites in its constellation. Figure 4: \(C/N_{0}\) behavior over time (mask angle and \(C/N_{0}\) limit not applied). Each panel refers to a single device and to a single GNSS. Panels in the first row, (**a–c**), refer to GPS; panels in the second row, (**d**,**e**), to Glonass; panels in the third row, (**f**,**g**), to Galileo; and panels in the fourth row, (**h**,**i**), to BeiDou. The panel in the first column, (**a**), refers to the Novatel device; panels in the second column, (**b**,**d**,**f**,**h**), to uBlox; and panels in the third column, (**c**,**e**,**g**,**i**), to Xiaomi. Similar conclusions can be obtained considering the maximum and minimum values: uBlox (and Novatel, even if for the GPS-only case), reported a higher maximum value than Xiaomi; Xiaomi, on the other hand, reported a higher minimum \(C/N_{0}\) value than uBlox, except for the BeiDou case. Although the devices were able to track very weak signals with \(C/N_{0}\) close to 10 dB-Hz, the measurements related to signals with such low power are not used in the estimation process because a threshold for the \(C/N_{0}\) value was set to 25 dB-Hz. Table 2 reports the mean \(C/N_{0}\) values for BeiDou measurements, classified by orbit type; it demonstrates that BeiDou measurements from MEO satellites have \(C/N_{0}\) values similar to those for GPS, while significantly lower values characterize GEO and IGSO cases. An additional analysis of \(C/N_{0}\) is carried out by comparing its trends for the G02 and G06 GPS satellites, for the three considered devices. In Figure 5, the \(C/N_{0}\) behavior for G02 is shown in panel (a), and that for G06 is shown in panel (b). As shown in Figure 5, the \(C/N_{0}\) values are about 48 dB-Hz with a very stable behavior for Novatel; slightly lower values with more pronounced fluctuations are evident for uBlox and even more for Xiaomi, remaining above 30 dB-Hz in any case. From Figure 5, it is evident that the \(C/N_{0}\) values are lower than those for the G02 case: for Novatel, \(C/N_{0}\) values are higher than those for uBlox and even higher than those for Xiaomi. It can be noticed that for uBlox and Xiaomi, the epochs in which Doppler measurements are available and CP measurements are not, marked by red dots in Figure 2, correspond to values of \(C/N_{0}\) below 25 dB-Hz. Usually, measurements from a satellite elevation below a certain threshold and with a \(C/N_{0}\) value below a certain limit are not used for solution computation. In this work, a mask angle of 15 degrees and a \(C/N_{0}\) limit of 25 dB-Hz are adopted. So, the numbers of