Methods And Performances Of Multi-System GNSS Positioning For Smartphones

The Global Navigation Satellite System(GNSS)can provide users with allweather positioning,navigation,and timing services.Since Google opened up the GNSS raw observation data interface for Android systems in 2016,using smartphones to collect GNSS raw observation data for high-precision positioning has become a research hotspot,but its positioning methods and performance need to be improved.This paper analyzes the quality of GNSS observation data from two smartphones and a geodetic GNSS receiver,and analyzes the methods and performance of pseudorange positioning,precise positioning,and carrier phase differential positioning for smartphones.The main research contents and results of the paper are as follows:(1)This study analyzed the GNSS observation data quality of the Trimble Alloy,Xiaomi 8,and Samsung S20,and found that there is a significant gap in GNSS signal quality between smartphones and professional GNSS receivers.Among the three devices,Trimble Alloy has the largest number of observable satellites,while Xiaomi 8has the least.The GDOP values for all three devices are relatively small,below 1.5,but the single-system DOP values for Xiaomi 8 and Samsung S20 are larger than the GDOP for GREC multi-system.Additionally,the signal-to-noise ratio(SNR)of Trimble Alloy is better than that of Samsung S20,and the SNR of Samsung S20 is better than that of Xiaomi 8.(2)The study examined the performance of single point positioning using smartphones.The pseudorange single-point positioning of geodetic professional receivers is significantly better than that of smartphones in the same environment.The Trimble Alloy receiver achieves a horizontal and vertical positioning accuracy of about1 meter,while the horizontal and vertical errors for smartphones are around 10 meters.For precise point positioning(PPP),the Xiaomi 8 smartphone achieves a sub-meterlevel horizontal accuracy and a vertical error of 3 meters in the multi-system GNSS PPP positioning mode.The improvement in horizontal accuracy for multi-system PPP and single GPS system PPP for Xiaomi 8 is not significant,but the improvement in vertical accuracy is 69.3%.(3)This study analyzed the performance of carrier phase differential positioning using smartphones.The Xiaomi 8 smartphone achieves a multi-system positioning accuracy of 0.64 m,0.70 m,and 1.20 m for the E,N,and U directions in static carrierphase differential positioning,which is better than single-system positioning,and the single GPS system is slightly better than the single BDS system.In dynamic carrierphase differential positioning experiments,the Xiaomi 8 smartphone can converge to within 1 meter after 100 seconds of walking in multi-system,while the dynamic carrierphase differential positioning effect of single GPS system and single BDS system is poorer.Due to signal blockage,some low-elevation satellites are susceptible to signal loss,which can lead to a maximum planar error of up to 4 meters.