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

An extrapolating unit for extrapolating the value of a navigation parameter (e.g., φkB or γkB) from a global positioning satellite as measured by a base receiver, said navigation parameter being transmitted to a rover receiver over a communication link in a sequence of consecutively provided frames, each frame comprising the measured value of the navigation parameter made for a specific time moment tk as designated by a clock in the base receiver, the start of each frame occurring at a time interval Tk from the start of the previous frame, the navigation parameter being extrapolated according to an extrapolation form comprising a constant, plus one or more terms which are a function of time, and one or more corresponding scaling parameters for scaling the terms, the values of said constant and scaling parameters being generated by said method, said extrapolating unit comprising:

• a receiving unit for receiving frames from the base station, each frame comprising a measured value of the navigation parameter, a representation of the specific time moment tk as designated by a clock in the base receiver at which the value was measured, and a weight factor Kk representative of the estimated quality of measured value of said frame;
• a monitoring unit to measure the signal-to-noise ratio of the communication link during the time each frame is received by the rover;
• a memory unit which capable of storing a plurality Mr of frames, said memory unit being responsive to the receiving unit and monitoring unit for storing the most recent consecutive frames received by the receiving unit and an indication representative of the signal-to-noise ratio of the communication link during the receipt of the corresponding stored frame;
• an assessment unit responsive to the signal-to-noise ratio, the weight factor Kk of the frame, which generates a quality indication associated with each stored frame of whether the measured value of a frame is satisfactory or unsatisfactory, said quality indication being generated as satisfactory unless one or more unsatisfactory conditions occurs, said quality indication being generated as unsatisfactory when the signal-to-noise ratio of the communication link falls below a first threshold value during the reception of the frame, said quality indication being generated as unsatisfactory when the weight factor Kk of the frame falls below a second threshold value during the reception of the frame;
• a discriminator for selecting, after each frame is received and stored, a subset of a number ns of the most recent frames from said set Mr of stored frames which have satisfactory quality indications;
• a processing unit for computing the values of the constant and scaling parameters of the extrapolation form from at least one selected subset of ns frames by an application of a least squares method which accounts for the weighting factors;
• and
• a generator for generating an extrapolated value of the navigation parameter frame from the extrapolation form for one or more time moments occurring after the time moment of the last received frame.