Satellite-based positioning includes deriving the location of a user’s receiver based on radio frequency signals transmitted by satellite systems. Current fully-operational Global Navigation Satellite Systems (GNSS) include the US GPS (Global Positioning System) and the Russian GLONASS (GLObalnaja NAvigatsionnaja Sputnikovaja Sistema). Satellite-based positioning is grounded in accurate time determination: the time difference between the transmitted and the received radio signal denotes the signal travel time, which reveals the distance between the satellite and the user antenna. Utilizing distance measurements between the user antenna and four different satellites, the receiver can obtain three-dimensional receiver coordinates in a global reference frame and the time difference between the receiver and satellite clocks.