GPS, fully known as the Global Positioning System, is a satellite-based radio navigation system that can provide accurate position, speed, and time information to global users. The working principle of GPS mainly involves the following steps:
- Satellite signal transmission: The GPS system is composed of multiple satellites. These satellites orbit the Earth and continuously broadcast radio signals containing time and position information to the Earth's surface.
- Signal reception: Users use GPS receivers to receive these satellite signals. The receiver is equipped with a high-precision clock for measuring the propagation time of the signals from the satellites to the receiver.
- Distance measurement: By measuring the propagation time of the signals, the receiver can calculate the distance to each satellite. This distance is called pseudo-range because it includes errors in the signal propagation time.
- Position solution: To determine the three-dimensional position of the receiver (longitude, latitude, and altitude), at least signals from four satellites are required. By establishing equation sets, the precise position of the receiver can be solved.
- Error correction: In the actual GPS positioning process, it will be affected by various factors, such as atmospheric delay (tropospheric delay and ionospheric delay), satellite orbital errors, receiver noise, etc. To improve the positioning accuracy, Differential GPS (DGPS) technology is usually adopted to reduce these errors through the correction information provided by the base station.
- Output of positioning information: After the GPS receiver calculates the position information, it can be output in various formats for the user's use, such as longitude and latitude coordinates, speed, time, etc.
Due to its characteristics of high accuracy, all-weather, and global coverage, the GPS system has been widely applied in fields such as military, civilian navigation, measurement, and timing. With the development of technology, the combined use of GPS with other satellite navigation systems (such as China's Beidou system, Russia's GLONASS system, and Europe's Galileo system) and ground base station positioning technologies makes the positioning service more accurate and reliable.
