Study On Rtcm Encoding And Message Predefinition For Compass System

Differential GNSS technology is widely used in satellite navigation and positioning technique. Receiving the differential corrections from the reference stations, the user can eliminate or reduce most of the positioning error. When we transport the differential correction from the reference station to the user through certain data links, we need to consider the data format of differential correction, and how to ensure the differential corrections data be right and integrate. Especially with today's rapidly development of communication technique, it is possible to transport differential GNSS data efficiently and accurately. Therefore, the mobile GNSS receiver can easily obtain the real-time differential corrections sourcing from a remote GNSS reference stations through the Internet or wireless network in order to improve positioning accuracy.RTCM recommended standards document has been developed by RTCM SC-104 to improve and promote the business of Differential GNSS service. Thanks to the development of RTCM, it has become widely used differential satellite navigation system standards throughout the world.Based on RTCM version 2.3, this paper analyzed the problems rising in the encoding of this standard, such as evaluating the validity and integrity of the parity algorithm, and finally designed the encoding program of RTCM message type. In light of COMPASS navigation system development, it is essential to predefine COMPASS RTCM message types to make COMPASS users use this differential GNSS service standards.In the introduction, the existing DGNSS agreements and the development of RTCM standards are introduced briefly.In chapter 2, firstly, the development of GNSS and COMPASS are described; Secondly, the principle of Differential GNSS positioning technology is expatiated; and the Networked Transport of RTCM via Internet Protocol- NTRIP is also introduced.Chapter 3 introduced RTCM 2.3 standard data format, and also argued the problem of encoding process, and ultimately coding system design process.In chapter 4, the COMPASS system characteristics are discussed; the COMPASS RTCM message types are predefined finally based on analyzing the existing GPS and GLONASS types of message.The conclusions and outlooks are given in chapter 5.The main research achievements are as follows:1. Partial RTCM version 2.3 Message Types is encoded. There are data to extract the original differential correction, in accordance with the RTCM message format for encoding data to fill to achieve coding procedures;2. Discuss how to use the Hamming Code to detect error, and analyze the validity of the parity algorithm;3. In accordance with the characteristics of COMPASS, predefining RTCM message types for COMPASS system.