Statistical Investigation of Android GNSS Data: Case Study Using Xiaomi Mi 8 Dual-Frequency Raw Measurements

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.