Methods and apparatuses of positioning a mobile user in a system of satellite differential navigation

Satellites of the GPS and GLONASS navigation systems broadcast code signals which are modulated onto respective carrier signals, and which are received by two receivers on Earth. The first receiver is situated at a point with known coordinates. The results of its measurements are transmitted to a user at a second receiver through a connection link, the user being interested in knowing his or her positioning. The second receiver is similar to the first receiver and it receives the signals of the same satellites. By processing data from the measurements of code delays and carrier phase shifts in the satellite signals received by two receivers, the methods and apparatuses of the inventions of the present application determine the location of the user with high precision and make the time indications of receiver clocks more accurate and exact. In the first invention, the measurements of two receivers are related to a common time moment by extrapolating measurement data that has arrived through the connection link with a delay. This common time moment is defined by the user. An extrapolating unit examines the measurements to find and discard measurements with abnormal errors. The unit then generates extrapolated measurement data (e.g., predictions) for the common time based upon the most reliable data. In the second invention, cycle slips in the phase-lock loops (PLLs) of the receivers, which may be caused by blockage of direct signals from the satellites, strong interference signals, and reflections, are detected and corrected in a multi-loop nonlinear tracking system. In the third invention, the procedure of resolution of phase measurement ambiguities comprises the preliminary estimation of floating ambiguities by a recurrent (e.g., iterative) procedure including the simultaneous processing of code and phase measurements for all satellites for each processing time interval, and the gradual improvement of the result as the information is accumulated. After the resolution of ambiguity, the user coordinates are estimated with centimeter accuracy on the basis of phase measurements on the carrier frequency.