Design And Implementation Of Real Time Differential Positioning Software Using Android Mobile Phones

In recent years,with the rapid development of navigation and positioning technology,the demand for location-based services has seen a blowout growth phenomenon,and behind this phenomenon,smart phones play an indispensable role.Google announced that it will open the GNSS raw observation interface on Android 7and above,makes it possible to achieve high precision on Android phones.Differential positioning technology is widely used in various industries due to its fast convergence speed and high positioning accuracy.With the maturity of differential positioning technology and the reduction of use cost,it is feasible to use differential technology to achieve high-precision positioning on Android phones.This article takes the open GNSS raw observation interface of Android mobile phones as the starting point,and utilizes exsiting high-precision positioning theory and related development technologies to study how to achieve differential positioning on mobile phones,in order to further expand research on high-precision positioning on mobile phones and improve people’s experience based on location services.The main research content of this thesis is as follows:(1)A detailed explanation was provided on the spatiotemporal reference,positioning error sources,observation values and equations,as well as differential positioning principles of the GNSS system,providing a theoretical basis for highprecision positioning of Android phones.Starting from the GNSS module of Android mobile phone,the APIs related to the GNSS observation values of the mobile phone and their meanings are systematically introduced.At the same time,it provides detailed instructions on how to use these APIs to calculate the pseudo range,carrier phase,Doppler and other observation values of mobile phones,achieving the acquisition of the original GNSS observation values of mobile phones,thus providing a data foundation for developing real-time differential positioning software on Android phones.(2)Design experiments to comprehensively analyze the quality of mobile phone GNSS observation data from the aspects of tracking satellite number,carrier-to-noise ratio,multipath error,and observation noise.The analysis results show that mobile phones have weak continuous tracking ability for satellites,and there are significant fluctuations in the number of tracking satellites;The average carrier-to-noise ratio of each system is 10-20 dBHz lower than that of the measurement receiver,and using a carrier-to-noise ratio height angle random model can better reflect the observed value noise;The multipath errors of the Mi8 phone L1 and L5 are 2.54 m and 1.06 m,respectively,and the P40 phone 1.46 m and 1.37 m,respectively,far exceeding the0.14 m and 0.13 m of the measurement receiver.Moreover,there are a large number of outlier noise points in the mobile phone observation values and the stability of the observation timing is poor.As a result,different quality control schemes were adopted to improve the accuracy of mobile phone single point positioning.The results showed that after comprehensive gross error detection and pseudo range smoothing,the single point positioning results were significantly improved.The Mi8 mobile phone increased by 52%,37%,and 36% in the E,N,and U directions,respectively,while the P40 mobile phone increased by 37%,26%,and 41% in the E,N,and U directions,respectively.(3)Starting from the Android system architecture and development environment,combined with the acquisition of mobile phone observations,real-time data communication and GNSS positioning knowledge,the real-time differential positioning software GNSS＿RTK for mobile phones was developed by using Java language and C language combined with JNI mixed programming technology with the help of Android Studio platform.The software has a friendly user interface and supports Rinex 3.03 version observation data and collection of original GNSS observation values of mobile phones,GNSS real-time high-precision differential positioning,star map,observation data,carrier-to-noise ratio,map and other visual display functions to meet different users demand.(4)Taking Mi8 and Huawei P40 as the research objects,dynamic and static experiments were designed to verify the positioning performance of the real-time differential positioning software GNSS＿RTK for mobile phones.The experimental data shows that under static open conditions,the planar positioning accuracy of Mi8 and P40 can reach 0.17 m and 0.15 m,and the positioning accuracy in the elevation direction is 0.25 m and 0.33 m respectively.The positioning accuracy decreases under static occlusion conditions,but it can still achieve the positioning accuracy of the sub-meter level in the plane and the meter level in elevation.In the dynamic experiment,the realtime plane positioning accuracy of the mobile phone was focused on.Using the software developed in this thesis in the walking and riding scenes,the plane positioning accuracy is within the meter level,which can fully meet the daily high-precision positioning needs of the public.Lane-level navigation at the meter level can be achieved under certain conditions,but in scenes such as large-area lakeside roads and urban canyons,it is difficult to achieve high-precision positioning due to poor positioning accuracy.The thesis includes 46 figures,and 21 tables,and 81 references.