Officially released on August 2016, the Android 7.0 has been a breakthrough for the Global Navigation Satellite System (GNSS) community. Starting with the introduction of its Application Programming Interface 24 (API 24), Android users have been able to directly access raw GNSS measurements within their smartphone, independently on the specific phone design or manufacturer. In this research we consider as a case-study device the Xiaomi Mi 8, equipped with the BCM47755 location hub (first dual-frequency GNSS chipset), after being upgrade to Android 9.0 in order to access new functionalities implemented in the API 28. The analysis of raw measurements and their quality is fundamental in smartphone-based positioning, since biased or extremely noisy estimates of the pseudorange measurements will hamper the precise positioning performances. Here, we report on several tests performed in static mode over a geodetic pillar, under similar conditions and covering time-spans up to several hours. Main quantities retrieved from the API were first described and then characterized based on the statistics retrieved from all these long dataset. After some considerations, a dependency w.r.t. the carrier-to-noise density ratio (C/N0) has been investigated for some of these variables, as well as for the impact of the API multipath indicator on the available observations. Finally, a preliminary C/N0-based trade-off between data ‘quantity’ and ‘quality’ is here proposed in order to support smartphone-based precise positioning.

This paper presents a first analysis on the positioning performance using raw GNSS dual-frequency measurements acquired by the Xiaomi Mi 8 smartphone. In our study, we used the code-only-based Single Point Positioning technique for epoch-by-epoch positioning, and the Precise Point Positioning technique, which is based on both code and carrier-phase measurements, on precise satellite orbit and clock corrections, as well as on a dynamic model to exploit the time-constant property of the phase ambiguities. The functional model used in both our own SPP and PPP algorithms is based on the uncombined GNSS observation equations. As the Xiaomi Mi 8 smartphone is able to track both GPS and Galileo systems in two frequencies, we will present results based on single and combined GNSS solutions in single- and dual-frequency mode. The performance of these solutions will be assessed in terms of their repeatability and accuracy with respect to the ground-truth, while the improvement in Android-based positioning with multiple frequencies and GNSSs will be assessed compared to the GPS L1-only SPP case. An optimal combination of the elevation cut-off angle and the carrier-to-noise density ratio mask will be explored in order to have a reasonable balance between availability and quality of observations. Both real-time and post-processing positioning results will be presented.