Research On High Precision Real-time GNSS Positioning Of Android Smartphone

The GNSS services in smartphones have been playing an important role in people's daily lives.At present,the positioning accuracy of smartphones is 5-10 m.Further improving of the positioning accuracy of smartphones will effectively improve the public user experience,and may introducing the convenience of smartphones into the field of traditional surveying and mapping.It will also help the development of high-tech frontier technologies such as Driverless,Internet of Things and Smart Cities.This paper is dedicated to improving the real-time positioning accuracy of smartphones without the use of non-GNSS data.Starting from the analysis of the data quality and the characteristic of the smartphone raw GNSS data,the existing GNSS positioning algorithms are improved,several GNSS positioning methods are applied to smartphones and their positioning performances are tested.The specific research work and its conclusions are as follows:1.The acquisition of the raw GNSS data of Android smartphones,the detailed analyse of its data characteristic and data quality.The mesurements such as satellite number,receiving time,and carrier phase through are obtained from the Android location service related API,and the pseudorange observations are calculated.The smartphones and the geodetic receivers are placed in the same place for synchronous observation,the raw GNSS observations of the two are compared,and the characteristic that the difference between the pseudorange observation and the carrier phase observation of smartphones are not fixed is anlysed in detail.The data quality of the smartphone G NSS observations is quantitatively analyzed,the analysis results show that the RMSE values of the smartphone pseudorange observations are within 4-12 m,the carrier phase observations change rate linear fitting RMSE values are 4-7 times that of geodesic receivers.According to the status quo of smartphone GNSS mesurements,a mobile phone GNSS positioning groess error processing method based on carrier phase observation uncertainty and filtering robustness algorithm is proposed2.Real-time high precision single point positioning for smartphones.According to the characteristic of smartphone raw GNSS observations,a corresponding carrier phase smoothing pseudorange scheme is given,and the carrier phase smoothing pseudorange single point positioning is realized on smartphones.Acorrding to the characteristic of GNSS observations and the data quality of smartphone,a modified real-time PPP positioning strategy which estimates two clock biases of smartphone is proposed,the reasonable filtering parameters are given,and the PPP is achieved on smartphones.The test results show that the Xiaomi MI8 smartphone's real-time PPP horizontal positioning error can converge to 2 m within 60 s,and to 1 m within 300 s.After convergence,the average horizontal and vertical RMSE are 0.47 and 1.64 m respectively.3.Real-time high precision differential positioning for smartphones.Based on the carrier phase smoothing pseudorange,the mobile phone pseudorange observations are differentially corrected,and the carrier phase smoothing pseudorange differential positioning is realized on smartphone.The test results show that the Xiaomi MI8 smartphone's real-time carrier phase smoothing pseudorange(smoothing window 30s)differential positioning average horizontal and vertical RMSE are 1.45 and1.93 m respectively.The smartphone raw GNSS observations and the reference station GNSS observations are combined into double-difference observations,according to the data quality of smartphone raw GNSS observations,a reasonable positioning model and filtering parameters are targeted,the real-time static and dynamic carrier phase double-difference positioning are achieved on smartphones.The test results show that the Xiaomi MI8 mobile phone's real-time static carrier phase double-difference positioning average horizontal and vertical RMSE are 0.31 and 0.46 m respectively after convergence,and the convergence time(horizontal error converges to 1m)is within 100 s.The RTK positioning horizontal and vertical RMSE are 0.64 and 0.72 m respectively.4.High precision real-time positioning APP development.The positioning theoretical algorithms are applied to actual APP development,using JAVA programming language and Android Studio platform,a real-time and post-hoc positioning APP is developed,which can achieve carrier phase smoothing pseudorange single point positioning,carrie phase smoothing pseudorange differential positioning,precise point positioning,static and dynamic carrier phase double-difference positioning.