Performance assessment of GNSS-IR altimetry using signal-to-noise ratio data from a Huawei P30 smartphone

Global Navigation Satellite System interferometric reflectometry (GNSS-IR) is a technique that utilizes multipath effects to sense the near-surface environment. Previous studies have focused on the retrieval performance of using geodetic GNSS equipment. Fortunately, Google announced in 2016 that smart devices running Android Nougat (7.0) operating system could provide raw GNSS measurements, which makes it possible to use a low-cost Android device to monitor the surrounding environment. In this study, we assessed the altimetry performance by using signal-to-noise ratio (SNR) data from a Huawei P30 smartphone, while a u-blox F9P receiver that is equipped with a low-cost antenna was placed next to the smartphone for comparison. Twenty days of SNR data from multiple GNSS constellations and signals were collected and processed. First, the characteristics of SNR data of Huawei P30 and u-blox F9P were compared and analyzed. For Huawei P30, it is observed that the SNR data have longer and clearer oscillations, which indicates that a higher range of elevation angles can be utilized. We further assessed the altimetry performance of Huawei P30 in different antenna orientations and different elevation angle ranges. It is shown that the effects of antenna orientation do exist. Meanwhile, the SNR oscillations become irregular when elevation angles exceed 60°, which suggests that SNR data with elevation angles below 60° can be used for Huawei P30. Finally, the altimetry performance of each signal was also assessed, and it is found that GPS L1, GLONASS G1, and BDS B1I could provide precise and stable height retrievals, while the performance of GPS L5 and Galileo E5a is slightly poorer. Overall, the Android smartphone possesses special cost and data availability superior to conventional GNSS equipment, making it a promising solution for GNSS-IR applications.