GNSS Precise Positioning Determinations Using Smartphones

Global Navigation Satellite System (GNSS) raw measurements are available on Smartphone running Android 7 since May 2016. This allows developers to access GNSS carrier phase and pseudorange measurements; therefore, precise positioning could be determined. Some limitation is that the location of the embedded GNSS antenna (and phase centre) within the Smartphones is not disclosed by any manufacturers. This paper aims to determine Xiaomi Mi8's GNSS antenna phase centre and its performances. The positioning accuracy is computed and later compared with a controlled position where the observations are obtained by a GNSS survey receiver; Trimble R10 where the nearest Continuously Operating Reference Station (CORS) with baseline length of approximately 5.3 km is used as reference base stations in relative positioning computations. Their positioning results are achieved from a commercial GNSS processing software; CHC Geomatics Office (CGO) version 1.0.6. It is found that the Mi8 GNSS antenna phase centre is located on the top left of the Smartphone; approximately 2.8 cm from the centre and 0.9 cm from the top edge. The Root Mean Square Error (RMSE) in Northings, Eastings and elevations are within centimetre level of accuracy when the screen is facing upwards. It could be concluded that a Smartphone Mi8 is capable to determine precise positions when the GNSS antenna phase centre is known and the integer phase ambiguities are correctly resolved.