Embedded Multi-frequency GNSS Single Epoch Dynamic RTK Positioning Technology

Satellite navigation technology has entered a new era of multi-system coexistence.Multisystem multi-frequency observation information provides more available data for improving positioning accuracy,real-time performance,and reliability.At this stage,due to the booming development of intelligent transportation,precision agriculture,express logistics,smart cities,Internet location services and sharing economy,satellite navigation and positioning technology has been applied more widely.Faced with numerous traditional and emerging market applications,satellite navigation and positioning technology not only needs to maintain its high accuracy and high reliability,but also needs to meet the application requirements of real-time dynamic positioning.Based on the above requirements,this paper focuses on the key technology of embedded multi frequency GNSS epoch-by-epoch kinematic RTK positioning technology in research.The main research work and contributions of the paper are as follows:(1)The Network RTK wide-lane positioning model based on BDS/GPS combination is determined.Firstly,based on the composition and service of CORS system,the advantages of network RTK positioning in VRS mode are analyzed.Then,the characteristics of the similar time-space reference of BDS and GPS are analyzed,and the BDS/GPS combination model is determined.Finally,the characteristics of dual-frequency and multi-frequency combined observations commonly used in GNSS positioning are analyzed,which provides a theoretical basis for the real-time BDS/GPS combination extra-wide-lane/wide-lane ambiguity resolution.(2)The embedded hardware platform based on GNSS board + ARM + Linux is developed.Firstly,the advantages of ARM and Linux in embedded development are analyzed,and by considering the development requirements,the micro2440 core board is selected as the embedded platform system board.At the same time,the GNSS board,power supply module,serial port module,storage module,and Ethernet modules etc.are integrated.Then,the cross development model and the transplantation of embedded Linux systems are explained to provide the software and hardware foundation for subsequent application software development.Finally,a vehicle INS/GNSS fusion dynamic verification platform based CORS is designed.And the real-time detection of commercial RTK terminals is achieved using the “quasi-zero baseline” approach,which verified the reliability and stability of the vehicle platform.(3)The embedded multi-frequency GNSS single epoch dynamic RTK positioning software is developed.Firstly,the overall framework of the software is designed based on the multi-task concurrent multi-threaded development and the functions of each thread are analyzed.Then,the real-time acquisition and decoding process of the local serial port and network differential GNSS data are discussed in detail.Finally,the BDS/GPS combination RTK positioning model is determined.And the real-time method of ambiguity resolution for extrawide-lane and wide-lane is elaborated in detail to implement the multi-frequency GNSS single epoch RTK positioning algorithm.(4)The dynamic test under real environment and statistical analysis of positioning results are conducted.Firstly,the continuity,space geometry,signal-to-noise ratio and multipath effect of the dynamic observation satellite of the GNSS board are analyzed,and the good quality of dynamic data is verified.Then,the dual frequency RTK zero-baseline positioning method is used to evaluate the accuracy of the range signal of GNSS board and verify the positioning advantage of the dual system.Finally,based on the vehicle INS/GNSS fusion dynamic verification platform,a zero-baseline dynamic test under real environment is carried out.And the reliability and stability of uninitialized centimeter-level positioning of embedded multifrequency GNSS wide-lane single epoch dynamic RTK is verified by comparing the postmortem results of the reference system of the vehicle verification platform and the real-time positioning results of the embedded rover station.