Development Report on BeiDou Satellite Navigation System-System Introduction
BeiDou Satellite Navigation System is a global satellite navigation system, which is designed and operated by China independently, and at the same time compatible with other satellite navigation systems worldwide.
BeiDou Satellite Navigation System consists of three parts, namely, space constellation, ground control and user terminal.
Space constellation consists of five GEO satellites and 30 Non-GEO satellites. The five GEO satellites are positioned at the equatorial longitudes of 58.75ºE, 80ºE, 110.5ºE, 140ºE and 160ºE. Non-GEO satellites consist of 27 MEO satellites and 5 IGSO satellites. Among them, MEO satellite orbit is 21,500 kilometers high, with an orbit inclination angle of 55º. And they are evenly distributed on three orbit planes. IGSO satellite orbit is 36,000 kilometers high, evenly distributed on three orbit planes, with an orbit inclination angle of 55º. The tracks of sub-satellite points of the three IGSO satellites coincide with each other. The intersection point is at 118ºE；phase difference is 120º.
Ground control consists of main control station, time synchronization station and monitor station. Tasks of the main control station include collecting the observation data of time synchronization stations and monitor stations, processing the data, generating satellite navigation message, uploading navigation message parameter onto the satellite, monitoring the effective load of satellite, completing mission planning and dispatching, and realizing the operation, control and management of the system. Time synchronization/uploading stations is mainly responsible for uploading satellite navigation message parameter, exchanging data with the main control station and measuring time synchronously on unified scheduling of the main control station. Monitoring station tracks and monitors the navigation satellite continuously, receives navigation signals and sends them to the main control station, and provides observation data to generate the navigation message.
User Terminal prefers to all kinds of BeiDou user terminals, including those compatible with other satellite navigation systems, in order to meet different application requirements of various fields and industries.
The time reference of BeiDou Satellite Navigation System is BeiDou Time (BDT). BDT applies international system of units (SI) second as elementary unit, without leap seconds. The initial epoch began from Coordinated Universal Time (UTC) 00:00:00, January 1st, 2006. The deviation between BDT and UTC maintains below 100 nanoseconds. The leap seconds information is broadcast in navigation message. The coordinate frame of BeiDou Satellite Navigation System is China Geodetic Coordinate System 2000 (CGCS2000).
After the completion of BeiDou Satellite Navigation System, it will provide satellite positioning, velocity measurement, and timing services for world users, and will provide wide area differential service with meter-level accuracy and message services with 120 words at a time for users in China and its neighboring areas. Its main function and performance index are as below：
- Main functions: positioning, velocity measurement, one-way or two-way timing, short message communication;
- Service region: global;
- Positioning accuracy: better than 10 meters;
- Velocity measurement accuracy: better than 0.2 meters/second;
- Timing accuracy: 20 nanoseconds.