Abstract: In a global positioning system, satellites transmit navigation signals to users which determine their position from the received navigation signals. A wide area differential correction system employs receiving stations in fixed positions on the ground and compares ranges between the receiving stations and the satellites measured from the navigation signals with the actual ranges between the satellites and the receiving stations to determine correction information including corrections in the satellite clock times and the satellite positions to be transmitted to the users and from which the users can more accurately determine their positions.

Abstract: In a global monitoring system having four or more satellites which transmit messages to user stations by which the user stations can determine the user position, the satellite messages include the time of transmission of the messages as indicated by satellite clocks and includes a correction message. The correction message consists of time correction values for the satellite clocks. The satellite time correction values are determined from a clocks only model wherein three or more monitoring stations having known positions on the ground receive the satellite messages and determine pseudoranges between the satellites and the monitoring stations. The satellite time correction values are determined statistically by nonlinear least squares from a clocks only model relating the ranges between the satellites and the monitoring stations to the measured pseudoranges, the satellite time correction values and monitoring stations time correction values.