1. Space part

　　The spatial part of GPS is composed of 24 working satellites, located at an altitude of 20 200 km above the surface, evenly distributed on 6 orbital planes (4 per orbital plane), with an orbital inclination of 55 °. In addition, there are three active backup satellites in orbit. The distribution of satellites allows for the observation of more than four satellites anywhere and at any time in the world, and allows for pre stored navigation information within the satellites. Due to atmospheric friction and other issues, the navigation accuracy of GPS satellites will gradually decrease over time.

　　2. Ground control system

　　The ground control system consists of a Monitor Station, a Master Monitor Station, and a Ground Antenna. The main control station is located in Colorado Spring, Colorado, USA. The ground control station is responsible for collecting information transmitted by satellites and calculating satellite ephemeris, relative distance, atmospheric correction, and other data.

　　3. User Equipment Section

　　The user equipment part is the GPS signal receiver. Its main function is to capture the selected test satellites according to a certain satellite cutoff angle and track their operation. After the receiver captures the tracked satellite signal, it can measure the pseudo distance and the rate of change of distance from the receiving antenna to the satellite, and demodulate data such as satellite orbit parameters. Based on these data, the microprocessor in the receiver can perform positioning calculations according to the positioning solution method, calculating the longitude and latitude, height, speed, time and other information of the user's geographical location. The receiver hardware, onboard software, and GPS data post-processing software package constitute a complete GPS user device. The structure of a GPS receiver is divided into two parts: an antenna unit and a receiving unit. The receiver generally uses two types of DC power sources, internal and external. The purpose of setting up the internal power supply is to continuously observe without interruption when replacing the external power supply. The battery automatically charges when using an external power source. After shutting down, the internal battery supplies power to the RAM memory to prevent data loss. At present, various types of receivers are becoming smaller in size and lighter in weight, making them convenient for field observation and use. Secondly, there are two types of user receivers: single frequency and dual frequency. However, due to price factors, most users purchase single frequency receivers.

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