Satellite-based positioning is grounded in accurate time computation that the time difference between the transmitted and the received radio signal indicate the signal travel time. It contain deriving the location of a user’s receiver based on radio frequency signals transmitted by satellite systems which show the distance between the satellite and the user antenna. The distance can measure between the user antenna and four different satellites that the receiver can get three-dimensional receiver coordinates in a global reference frame and the time difference between the receiver and satellite clocks.