The Beidou Satellite Navigation and Positioning System is a regional active three-dimensional satellite positioning and communication system (CNSS) independently developed by China. It is the third mature satellite navigation system after GPS from the United States and GLONASS from Russia.
System composition and working principle
The Beidou satellite positioning system consists of two geostationary satellites (800E and 1400E), one in orbit backup satellite (110.50E), a central control system, a calibration system, and various user machines. The working process of the system is as follows: firstly, the central control system sends inquiry signals to satellite I and satellite II simultaneously, and broadcasts to users within the service area of the satellite repeater. The user responds to the inquiry signal from one of the satellites and simultaneously sends response signals to both satellites, which are then forwarded back to the central control system via the satellite. The central control system receives and demodulates signals sent by users, and then performs corresponding data processing based on the requested service content. For positioning applications, the central control system measures two time delays: the delay when an inquiry signal is sent from the central control system, forwarded to the user via a certain satellite, and the delay when the user sends a positioning response signal, forwarded back to the central control system via the same satellite; The delay of sending an inquiry signal from the central control system to the user via the same satellite, and the user sending a response signal, which is then forwarded back to the central control system via another satellite. Due to the known positions of the central control system and the two satellites, the distance between the user and the first satellite, as well as the sum of the distances between the user and the two satellites, can be calculated from the above two delay quantities, thus knowing that the user is on the intersection line between a sphere centered on the first satellite and an ellipsoid centered on the two satellites. In addition, the central control system can retrieve the user's elevation value from the digital topographic map stored in the computer, and also know that the user is on an ellipsoid parallel to the Earth's reference ellipsoid. Thus, the central control system can ultimately calculate the three-dimensional coordinates of the user's location, which are encrypted and sent to the user via the outbound signal.
The coverage area of the Beidou satellite positioning system is the heart region between 5 ° N and 55 ° N latitude and 70 ° E and 140 ° E longitude, with the upper part being larger and the lower part smaller, and the widest point being around 35 ° N latitude. Its positioning accuracy is a horizontal accuracy of 100m (1 σ), and after setting up a calibration station, it is 20m (similar to differential state). Operating frequency: 2491.75 MHz. The system can accommodate 540000 users per hour.
Due to the need for user terminals to send positioning signals to positioning satellites during positioning, the user's position is calculated based on the difference in the time the signals arrive at the positioning satellite, hence it is called "active positioning".
The Three Major Functions of the Beidou System
Fast positioning: The Beidou system can provide all-weather, high-precision, fast real-time positioning services for users within the service area, with a positioning accuracy of 20-100m;
Short message communication: The Beidou system user terminal has bidirectional message communication function, and users can transmit short message information of 40-60 Chinese characters at once;
Precision timing: The Beidou system has a precision timing function, which can provide users with a time synchronization accuracy of 20ns-100ns.
Advantages and disadvantages of the system
Advantages:
Compared with GPS in the United States and GLONASS in Russia, it has added communication functions.
24/7 fast positioning, comparable to GPS accuracy.
Safe and reliable, with strong confidentiality.
Inferiority:
The Beidou system is an active positioning system with limited system capacity and complex positioning terminals.
The Beidou system belongs to the regional positioning system and can currently only provide positioning services for China and surrounding areas.
Application of Beidou System
In 2000, two satellites of the Beidou Navigation and Positioning System were successfully launched, marking that China had its own first generation satellite navigation and positioning system. This has significant economic and social significance for meeting the needs of China's national economy and defense construction, promoting the development of China's satellite navigation and positioning industry. The Beidou Navigation and Positioning System consists of three parts: Beidou Navigation and Positioning Satellite, Ground Control Center, and Beidou User Terminal.
The service area of the Beidou Navigation and Positioning System is China and surrounding countries and regions. It can determine the geographic latitude and longitude information of users at any time and any place within the service area, and provide two-way short message communication and precise timing services. The Beidou system can be widely applied in various industries such as ship transportation, road transportation, railway transportation, maritime operations, fishery production, hydrological forecasting, forest fire prevention, environmental monitoring, as well as other units with special command and dispatch requirements such as the military, public security, customs, etc.
Five advantages of Beidou application
Simultaneously possessing positioning and communication functions, without the need for support from other communication systems;
Covering China and surrounding countries and regions, providing 24-hour service without communication blind spots;
Specially suitable for large-scale monitoring and management of group users, as well as data collection and transmission applications for users in unsupported areas;
The unique central node based positioning processing and command type user machine design can simultaneously solve the problems of "where am I" and "where are you";
Autonomous system, high-strength encryption design, secure, reliable, and stable, suitable for critical departmental applications.
