Abstract
In May 2016, the availability of GNSS raw measurements on smart devices was announced by Google with the release of Android 7. It means that developers can access carrier-phase and pseudorange measurements and decode navigation messages for the first time from mass-market Android-devices. In this paper, an improved Hatch filter algorithm, i.e., Three-Thresholds and Single-Difference Hatch filter (TT-SD Hatch filter), is proposed for sub-meter single point positioning with raw GNSS measurements on Android devices without any augmentation correction input, where the carrier-phase smoothed pseudorange window width adaptively varies according to the three-threshold detection for ionospheric cumulative errors, cycle slips and outliers. In the mean time, it can also eliminate the inconsistency of receiver clock bias between pseudorange and carrier-phase by inter-satellite difference. To eliminate the effects of frequent smoothing window resets, we combine TT-SD Hatch filter and Kalman filter for both time update and measurement update. The feasibility of the improved TT-SD Hatch filter method is then verified using static and kinematic experiments with a Nexus 9 Android tablet. The result of the static experiment demonstrates that the position RMS of TT-SD Hatch filter is about 0.6 and 0.8 m in the horizontal and vertical components, respectively. It is about 2 and 1.6 m less than the GNSS chipset solutions, and about 10 and 10 m less than the classical Hatch filter solution, respectively. Moreover, the TT-SD Hatch filter can accurately detect the cycle slips and outliers, and reset the smoothed window in time. It thus avoids the smoothing failure of Hatch filter when a large cycle-slip or an outlier occurs in the observations. Meanwhile, with the aid of the Kalman filter, TT-SD Hatch filter can keep continuously positioning at the sub-meter level. The result of the kinematic experiment demonstrates that the TT-SD Hatch filter solution can converge after a few minutes, and the 2D error is about 0.9 m, which is about 64%, 89%, and 92% smaller than that of the chipset solution, the traditional Hatch filter solution and standard single point solution, respectively. Finally, the TT-SD Hatch filter solution can recover a continuous driving track in this kinematic test.
Highlights
As a general impression, we can get a rough position through the consumer-grade chipset in smartphones based on Global Navigation Satellite System (GNSS) observations
With the release of Android 7, Google announced that the raw GNSS measurements in Android smart devices can be exported and used through the API (Application Programming Interface) at the application level
Based on the above analysis, we eliminate the receiver clock inconsistency between the pseudorange and the phase by the single difference between the satellites. We introduce these three threshold detections into the Hatch filter to adaptively adjust the smoothing window length, in order to weaken the influence of the ionosphere cumulative errors, cycle slips, and gross errors
Summary
We can get a rough position through the consumer-grade chipset in smartphones based on Global Navigation Satellite System (GNSS) observations. Achieving positioning and navigation with sub-meter-level accuracy on smart devices with a consumer-grade chipset is an important application for the future development of mass-market GNSS [4]. From 2017 to 2020, GNSS receivers in the global market will grow from 5.8 billion to 8.0 billion, in which the smart portable devices that people use almost every day account for almost 80% of the total amount [6]. It means that research on high-precision positioning and navigation of smart devices has great prospects in the market. The official Android documentation illustrates most Android 7.0 or higher smart devices manufactured in 2016 or later can provide raw GNSS data [7]
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