GPS satellites continuously send radio signals with time and position information in the sky day and night for reception by GPS receivers. Satellite time is generated by on-board atomic clocks. The position information of the satellite (satellite orbit parameters, also known as ephemeris) is sent to the satellite regularly by the ground control station, which is called "injection", and then broadcast to the user receiver through the satellite.
Use triangulation method to measure the distance between three or more satellites and the GPS receiver, and determine the position of the GPS receiver on the earth or in the sky from the distance. Since the three-dimensional position of the receiver needs to be determined, signals from at least three satellites must be received.
The distance is determined by measuring the time (interval) for the satellite signal to reach the receiver from the satellite. There is a period of time between the time when the signal is received by the receiver and the time when the signal is transmitted by the satellite. This time interval is usually called delay. The satellite and receiver generate the same pseudo-random code at the same time. Once the two codes are time synchronized, the receiver can measure the delay, multiply the delay by the speed of light, and get the distance.
Use triangulation method to measure the distance between three or more satellites and the GPS receiver, and determine the position of the GPS receiver on the earth or in the sky from the distance. Since the three-dimensional position of the receiver needs to be determined, signals from at least three satellites must be received.
The distance is determined by measuring the time (interval) for the satellite signal to reach the receiver from the satellite. There is a period of time between the time when the signal is received by the receiver and the time when the signal is transmitted by the satellite. This time interval is usually called delay. The satellite and receiver generate the same pseudo-random code at the same time. Once the two codes are time synchronized, the receiver can measure the delay, multiply the delay by the speed of light, and get the distance.