Development And Application Of Network RTK Communication Key Module

Network RTK technology has an advantage of wide coverage, high positioning accuracy, reliability, etc., so it has been widely used in the field of measurement and navigation. Network RTK system generally consists of a reference station, computing and control center, mobile users and the necessary data communication link.Among them, fast, reliable data transmission is a necessary condition of the network RTK.This paper not only introduces the RS-232 interface, basic principle of serial ports communication and API underlying function, but also module structure of board K503 from Sinan navigation receiver, information type, command format and data protocols.We have achieved the command sending, data type setting, required data acceptance andbinary data stream decoding about the original observation and satellite ephemeris using RS-232 serial line based on Visual 2010 development environment. Network RTK reference station receivers are generally connected to the modem via RS-232 serial line, and these data like the original observations are sent to the data management center of CORS station via VPNinternet line.This paper introduces the TCP/IP network communication protocol model, Winsock network programming principles, TCP client/server development and FTP client/server development based on Winsock language. We have imitated TCP network communication between client and server based on Visual 2010 development environment. So binary data stream can be transmitted not only between base station and computation and control center but also between calculation and control centers and post-processing user via Internet(TCP/IP access)by IP address and port number.We have imitated FTP network communication between client and server. So users can obtain the latest, useful RINEX data files, for example, users can download SP3 precise ephemeris files, observationfiles, navigationfiles, etc. from the IGS station ‘Anonymous’ server.This paper introduces the message format of the latest version RTCM3.1, content andencoding and decoding algorithmof important message, principle and achievement of Ntrip network transmission.Visit Jiangsu CORS station according to network transmission communication protocol(ie Ntrip protocol), upload user authorization information(IP address, port number, user name, password) and approximate location(GPGGA of NMEA protocol) to receive virtual observations of rover station. Decode the message RTCM1004, RTCM1005 from Sinan board and verify the correctness of encoding and decoding algorithm.Finally, we initially carry out RTK/IMU navigation product development and software implementation with the use of serial communication module, network communication module(TCP communications), Ntrip module and data transmission protocol codec algorithm.