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 Mi8u0027s 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.

Helmert Variance Component Estimation for MultiGNSS Relative Positioning The Multiconstellation Global Navigation Satellite System (MultiGNSS) has become the standard implementation of high accuracy positioning and navigation applications. It is well known that the noise of code and phase measurements depend on GNSS constellation. Then, Helmert variance component estimation (HVCE) is usually used to adjust the contributions of different GNSS constellations by determining their individual variances of unit weight. However, HVCE requires a heavy computation load. In this study, the HVCE posterior weighting was employed to carry out a kinematic relative MultiGNSS positioning experiment with six shortbaselines from day of year (DoY) 171 to 200 in 2019. As a result, the HVCE posterior weighting strategy improved MultiGNSS positioning accuracy by 20.5%, 15.7% and 13.2% in eastnorthup (ENU) components, compared to an elevationdependent (ED) priori weighting strategy. We observed that the weight proportion of both code and phase observations for each GNSS constellation were consistent during the entire 30 days, which indicates that the weight proportions of both code and phase observations are stable over a long period of time. It was also found that the quality of a phase observation is almost equivalent in each baseline and GNSS constellation, whereas that of a code observation is different. In order to reduce the time consumption of the HVCE method without sacrificing positioning accuracy, the stable variances of unit weights of both phase and code observations obtained over 30 days were averaged and then frozen as a priori information in the positioning experiment. The result demonstrated similar ENU improvements of 20.0%, 14.1% and 11.1% with respect to the ED method but saving 88% of the computation time of the HCVE strategy. Our study concludes with the observations that the frozen variances of unit weight (FVUW) could be applied to the positioning experiment for the next 30 days, that is, from DoY 201 to 230 in 2019, improving the positioning ENU accuracy of the ED method by 18.1%, 13.2% and 10.6%, indicating the effectiveness of the FVUW.