What Is The GPS System Principle?

- Jun 28, 2018 -

What is the GPS system principle?


When the Soviet Union launched the first artificial satellite, researchers at the Applied Physics Laboratory at John Hobbs King University in the United States proposed that since the position of the observatory can be known to know the position of the satellite, if the position of the satellite is known, it should also be able to measure The recipient's location. This is the basic idea of navigation satellites. The basic principle of the GPS navigation system is to measure the distance from the known position of the satellite to the user's receiver, and then integrate the data of multiple satellites to know the specific location of the receiver.


Best In Car Camera Dash Cam Dual Update Icloud Support With GPS For Car.jpgTo achieve this goal, the position of the satellite can be detected in the satellite ephemeris according to the time recorded by the satellite clock. The distance from the user to the satellite is obtained by recording the time it takes for the satellite signal to travel to the user and multiplying it by the speed of light (due to atmospheric ionospheric interference, this distance is not the actual distance between the user and the satellite, but Pseudorange (PR): When the GPS satellites work normally, they will continuously transmit navigation messages with pseudo-random codes consisting of 1 and 0 binary symbols (pseudo-codes). There are two types of pseudo-codes used by GPS systems: Civilian C/A code and military P(Y) code: C/A code frequency is 1.023MHz, repetition period is one millisecond, code spacing is 1 microsecond, equivalent to 300m, P code frequency is 10.23MHz, repetition period is 266.4 days, code The spacing is 0.1 microseconds, which is equivalent to 30m, and the Y code is formed on the basis of the P code, and the security performance is better.The navigation message includes satellite ephemeris, work status, clock correction, ionospheric delay correction, atmospheric refraction correction, etc. It is derived from the satellite signal -{A|zh-cn: demodulation; zh-tw: demodulation variable} - to 50b/s-{A|zh-cn: modulation; zh-tw: modulation }-Emitted on the carrier frequency. Each main frame of the navigation message contains 5 sub-frames each of which is 6 seconds long. The first three frames each have 10 words. Repeat once every thirty seconds, once per hour, and the next two frames total 15000b.The contents of the navigation message mainly include telemetry code, conversion code, and 1, 2, and 3 data blocks, the most important of which is ephemeris data. When the user receives the navigation message, it extracts the satellite time and compares it with his own clock to know the distance between the satellite and the user, and uses the satellite ephemeris data in the navigation message to calculate where the satellite transmits the message. The position, the user's position and speed in the WGS-84-{A|zh-cn: geodetic coordinate system; zh-tw: geodetic coordinate system} can be known.

It can be seen that the role of the satellite part of the GPS navigation system is to continuously launch navigation messages. However, since the clock used by the user's receiver and the satellite-borne satellite clock cannot always be synchronized, in addition to the user's 3D-{A|zh-cn:coordinate;zh-tw:coordinate}-x,y,z, To introduce a Δt, which is the time difference between the satellite and the receiver, as an unknown, solve the 4 unknowns with 4 equations. So if you want to know the location of the receiver, you must be able to receive at least four satellite signals.