1、 GPS overview
The current satellite navigation systems mainly include the US GPS, the Russian GLONASS, the European Galileo, and the Chinese COMPASS. The US GPS system is used more.
The system consists of three parts:
(1) Space satellite part: consisting of N satellites, operating in different orbits. Each satellite continuously transmits radio waves with satellite orbit and time information for reception by receiver equipment on the Earth.
(2) Ground control part: Tracking and controlling the monitoring control points of the above satellite operations.
(3) Receiver part: It can receive all GPS satellite signals and calculate the coordinates, moving speed and time of the receiver's position in real time.
2、 GPS receiver
GPS receivers are now typically 12 channels and can receive 12 satellites simultaneously.
GPS signal reception needs to be in the open sky. It is also attenuated by atmospheric gases, clouds, rain, fog, etc. Therefore, sometimes the weather is not good and the satellite signal is not good.
Strong electromagnetic signals can also interfere with GPS signals.
3、 GPS atomic time
The traditional GPS signal consists of three parts: a data code (navigation message), a ranging code (C/A code), and a carrier (L1 and L2). The role of the GPS receiver is to receive the satellite signal from GPS, output UTC time and 1pps, where UTC time is the time information of year, month, day, minute, minute and second, and its starting point is the rising edge of 1pps second pulse. The receiving device can perform precise time + frequency synchronization through these two pieces of information.
Different time systems are used in different GNSS systems, and detailed information can be found online.
