How GPS works:
An atomic clock is installed on satellites which continuously keeps sending the radio signals to earth’s surface which our mobile phone or cars receiver catch as shown in the image below:
As the satellites sends the radio signals to the receiver the time difference of when the signal is sent and the signal received is calculated by multiplying it with the speed of light. As the number satellite sending the signals increases the accuracy of where we are also increase since GPS system works on trilateration and triangulation. A 1 second delay on the speed of signal sent from the satellite can cause up to 1 foot of miscalculation. By the year 2020 we will be having satellites with high accuracy Atomic Clock by the help of which the error can be minimized.