Research And Software Development Of High Precision Differential System Based On Android Mobile Smart Terminal

China has the largest mobile smart terminals market in the world,it possesses billions of smart devices with satellite positioning capabilities.With the rapid development of satellite positioning technology,humans have higher and higher requirements for positioning accuracy of mobile smart terminals.However,due to the limitation of the hardware conditions of the mobile smart terminal itself and the use of a single point positioning technology,it can only achieve a dynamic accuracy of about 7 meters,which limits the application range.Differential positioning technology is more accurate than single point positioning technology,so it is possible to improve accuracy for more applications.In order to meet users' demand for high-precision positioning,this paper combines the satellite navigation chip API of Android 7.0 and above system mobile smart phones to support the development trend of output pseudo-range and carrier phase,and the characteristics of RTK dynamic high-precision positioning.A solution based on RTK real-time differential technology to realize high-precision positioning of Android mobile smart phone is proposed.This paper has independently developed a set of dedicated high-precision real-time dynamic positioning software GNSSRTK GDUT that can be downloaded and installed.It utilizes the inexpensive satellite navigation chip and antenna that the mobile smart phone brings,and can work with nearby differential reference base stations without changing any hardware conditions.The differential server constitutes a high-precision differential positioning system;it corrects the satellite ephemeris error,satellite clock error,ionosphere error,and tropospheric error that have the largest influence on positioning,and improves its positioning accuracy from 7 meters to 2 meters,enabling real-time dynamic positioning.When the user needs to use it,it is only necessary to install an APP on the Android mobile smart phone.Firstly,combining the mobile smart phone,design the working framework of the differential positioning system and choose the best differential positioning technology.Using the Nov Atel OEM615 as a reference base station and the ublox 8t as the mobile station,the pseudo range differential and RTK positioning data are collected respectively,and the collected data is analyzed by CEP precision.Secondly,it has independently developed a set of positioning software involving 40,000 lines of code.Its internal RTK solver module overall design is divided into four steps: the first step,according to the receiver observations in the inter-station and inter-satellite seeking a difference;the second step,adding EKF algorithm to update the positioning status;In the third step,the whole-period ambiguity in the carrier phase is solved by using the LAMBDA algorithm.In the fourth step,in order to compensate for the low accuracy of the RTK initial solution in the positioning software,a mini-batch gradient descent algorithm is introduced in the RTK solver module of the positioning software.The parameters of the covariance model affecting the positioning are repeatedly debugged,so that the positioning accuracy is improved,that is,the error between the coordinates finally calculated by the positioning software and the RTK positioning result of the target value ublox 8t reaches a minimum value.Finally,build the experimental platform and configure the experimental parameters,test the positioning software and verify the positioning effect.In the static test,two sets of fixed point data are compared;in the dynamic test,the positioning trajectories output by the positioning software are compared with the nexus 9 single point positioning trajectory and the ublox 8t reference trajectory and four sets of dynamic data are compared according to baseline lengths of 20 m,1km,3km,and 5km.The experimental results show that the accuracy of the improved positioning software is less than that of ublox 8t,but far greater than that of nexus 9 itself.The positioning accuracy improves the positioning accuracy of nexus 9 from 7 meters to 2 meters overall.