# A Controlled-Environment Quality Assessment of Android GNSS Raw Measurements
## 4 Results and Discussion
### Analysis of Raw Measurements  
Satellite visibility in all the devices was comparable, and raw measurements of seven GPS L1 signals that were visible throughout the observation period were processed. As an example, Figure 9  
Figure 8: Simulated satellite constellations and related Horizontal Dilution Of Precision (HDOP) for record and replay experimental scenarios. (**a**) Skyplot of simulated satellites; (**b**) number of visible satellites and HDOP.  
Figure 7: Record and Replay equipment and configuration for controlled experiments.  
plots the \(C/N_{0}\) values of GPS PRN 3 for all Android devices being tested. A similar trend could be seen for all other visible PRNs. The \(C/N_{0}\) of both Huawei models was more stable, with standard deviations (STDs) of around 0.08 dB with respect to the Nexus 9, with around 0.14 dB STD. Nevertheless, values were 3 dB lower than the latter. Interestingly, the Nexus 9 \(C/N_{0}\) values were also a close match to the reference benchmark receiver. The cause of a slight spike in \(C/N_{0}\) value around 320 s in the Huawei devices could not be determined, and could be due to a manufacturer setting.  
It was seen that, on the Huawei models, after \(t^{*}=210\) s of the start of logging, the raw measurements considerably deteriorated. The STDs of the \(C/N_{0}\) before and after this were around 0.04 dB and 0.09 dB, respectively. This deterioration caused a significant difference in measurements. On observing no change in the HardwareClockDiscontinuityCount parameter (which gives the count of the receiver clock discontinuities [6]) of the Google Toolbox output during the entire observation period, it could be assumed that, even though the primary TCXO clock was running, the GNSS tracking chipset was turned off.  
Figure 10 plots the detrended code pseudorange deviation (lower panel) compared with the AccumulatedDeltaRangeState parameter for GPS PRN 23 (upper panel). Such a flag indicates whether the range measurements is reset or there is a cycle slip due to a loss of lock [6]. The quality between the code and carrier pseudorangeswasis compared by calculating their detrended STDs. For short time spans, detrended pseudorange measurements could be considered as an ergodic process, and were obtained through second-order differentiation [7]. From the figure, it can be seen that there was a failure to achieve an ambiguity fix in the Huawei models after \(t^{*}\), but there were no cycle slips before this mark. The pseudorange noise remains within 2 m for all PRNs before a duty cycle occurred. In the Nexus 9, there were no cycle slips during the tested 10 min interval, and the noise remained within 4 m. This was observed in all other available PRNs. The continuity of a high-variability detrended pseudorange is due to the switching of clocks when a duty cycle occurs [6]. The detrended code- and carrier-phase pseudorange STDs of the Huawei devices before the power-saving function were within 3 m and 12 mm, respectively, whereas, for the Nexus 9, they were within 6 m and 13 mm. In comparison, the detrended benchmark receiver-code pseudorange STDs were within 1.5 m.  
Figure 9: \(C/N_{0}\) comparison between Android devices in a controlled environment.