Abstract
The opening access of global navigation satellite system (GNSS) raw data in Android smart devices has led to numerous studies on precise point positioning on mobile phones, among which single-frequency precise point positioning (SF-PPP) has become popular because smartphone-based dual-frequency data still suffer from poor observational quality. As the ionospheric delay is a dominant factor in SF-PPP, we first evaluated two SF-PPP approaches with the MGEX (Multi-GNSS Experiment) stations, the Group and Phase Ionospheric Correction (GRAPHIC) approach and the uncombined approach, and then applied them to a Huawei P40 smartphone. For MGEX stations, both approaches achieved less than 0.1 m and 0.2 m accuracy in horizontal and vertical components, respectively. Uncombined SF-PPP manifested a significant decrease in the convergence time by 40.7%, 20.0%, and 13.8% in the east, north, and up components, respectively. For P40 data, the SF-PPP performance was analyzed using data collected with both a built-in antenna and an external geodetic antenna. The P40 data collected with the built-in antenna showed lower carrier-to-noise ratio (C/N0) values, and the pseudorange noise reached 0.67 m, which is about 67% larger than that with a geodetic antenna. Because the P40 pseudorange noise presented a strong correlation with C/N0, a C/N0-dependent weight model was constructed and used for the P40 data with the built-in antenna. The convergence of uncombined SF-PPP approach was faster than the GRAPHIC model for both the internal and external antenna datasets. The root mean square (RMS) errors for the uncombined SF-PPP solutions of P40 with an external antenna were 0.14 m, 0.15 m, and 0.33 m in the east, north, and up directions, respectively. In contrast, the P40 with an embedded antenna could only reach 0.72 m, 0.51 m, and 0.66 m, respectively, indicating severe positioning degradation due to antenna issues. The results indicate that the two SF-PPP models both can achieve sub-meter level positioning accuracy utilizing multi-GNSS single-frequency observations from mobile smartphones.
Highlights
Precise positioning performance with smartphones that employ low-cost global navigation satellite system (GNSS) chips has attracted increasing attention in both academic and industrial communities in the past few years
Studies have shown that GNSS observations from Android devices suffer from severe data quality problems and many of them are very different compared to geodetic grade receivers [1,2,3]
The timedifference filtering approach was adopted to suppress the systematic errors in Nexus 9 tablet data, and the results showed that the root mean square (RMS) error of the static positioning solution was less than 0.6 and 1.4 m in the horizontal and vertical directions, respectively [1]
Summary
Precise positioning performance with smartphones that employ low-cost GNSS chips has attracted increasing attention in both academic and industrial communities in the past few years. Studies have shown that GNSS observations from Android devices suffer from severe data quality problems and many of them are very different compared to geodetic grade receivers [1,2,3]. They are subject to low signal strength, high measurement noise, and poor multipath suppression, and to some unexpected errors that may be hardware-related. Some other errors were noticed for different smartphones, especially the irregular gain pattern of these low-cost antennas [6,7], the drifts between the code and carrier-phase observables [5], and the arbitrary initial phase offset [8,9] These factors are non-negligible in performing precise positioning.
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