Patent ID: 6020846
Filing Date: 2000-02-01
Classification: G01S

Abstract:
In a global positioning method of determining the position of a user station from a global positioning system comprising at least four satellites and at least three monitoring stations, said method comprising transmitting time messages from said satellites to said monitoring stations, said time messages indicating the time of transmission of said time messages in accordance with the corresponding satellite clocks, detecting the time of receipt of said time messages by said monitoring stations, said satellites sending said user station a correction message to correct for errors in said global positioning system including clock biases and other global positioning system errors, the position of the user station being determined from the difference between the time of transmission of said time messages and the time of receipt of said time messages and the information in said time correction message, the improvement wherein said correction message comprises satellite transmission time correction values which incorporate said clock biases and corrections for said other global positioning system errors, said correction values being determined from a clocks only model relating the ranges between said satellites and said monitoring stations to measured pseudo ranges between said satellites and said monitoring stations corrected by said satellite transmission time correction values and by monitoring station time correction values, said monitoring station time correction values correcting the time of receipt of said time messages by said monitoring stations in said clocks only model, said satellite transmission time correction values and said monitoring station time correction values being determined statistically in accordance with the closest fit of measured pseudo ranges between satellites and said monitoring stations to said clocks only model.