Method for generating clock corrections for a wide-area or global differential GPS system

A method for generating GPS satellite clock corrections. comprising:

• obtaining dual-frequency pseudorange code measurements and carrier-phase measurements from a plurality of satellites;
• for each of the plurality of satellites, forming a smoothed refraction-corrected code measurement based on the dual-frequency pseudorange code measurements and carrier-phase measurements from the satellite;
• and
• computing clock corrections for the plurality of satellites based on the smoothed refraction-corrected code measurements;
• wherein the dual-frequency pseudorange code measurements and carrier-phase measurements from each of the plurality of satellites includes a pseudorange code measurement and a carrier-phase measurement corresponding to each of two carrier signal frequencies and at each of a series of measurement epochs, and wherein forming the smoothed refraction-corrected code measurement for each satellite comprises:
• for each of the series of measurement epochs and for each carrier signal frequency, forming a linear combination of the carrier-phase measurements corresponding to the two carrier signal frequencies from the satellite, such that the linear combination of the carrier-phase measurements matches ionospheric refraction effects on the pseudorange code measurement for the carrier signal frequency from the satellite;
• forming a smoothed code measurement for each carrier signal frequency by smoothing the pseudorange code measurements for the carrier signal frequency with the matching linear combinations of the dual-frequency carrier-phase measurements;
• and
• computing the smoothed refraction-corrected code measurement based on the smoothed code measurements for the two carrier signal frequencies.

A method for generating GPS satellite clock corrections, comprising:

• obtaining dual-frequency pseudorange code measurements and carrier-phase measurements from a plurality of satellites;
• for each of the plurality of satellites, forming a smoothed refraction-corrected code measurement based on the dual-frequency pseudorange code measurements and carrier-phase measurements from the satellite;
• and
• computing clock corrections for the plurality of satellites based on the smoothed refraction-corrected code measurements;
• wherein the dual-frequency pseudorange code measurements and carrier-phase measurements are obtained at a reference GPS receiver having a known location and wherein computing the clock corrections comprises:
• computing a residual for each of the plurality of satellites by subtracting a theoretical range between the reference GPS receiver and the satellite from the smoothed refraction-corrected code measurement for the satellite;
• forming a mean receiver clock error as a linear combination of the residuals for the plurality of satellites;
• and
• computing a clock correction for each of the plurality of satellites by subtracting the mean receiver clock error from the residual computed for the satellite.

A method for generating satellite clock corrections for a wide-area GPS network having a plurality of reference stations including a master reference station and a plurality of local reference stations, comprising:

• for each reference station, obtaining a smoothed refraction-corrected code measurement for each satellite visible to the reference station formed using GPS measurements taken from the satellite at the reference station;
• computing a master clock correction for each satellite visible to the master reference station using the smoothed refraction-corrected code measurements for the master reference station;
• for each of the plurality of local reference stations, computing a local clock correction for each satellite common to the master reference station and the local reference station using smoothed refraction-corrected code measurements for the master reference station and for the local reference station;
• and
• computing an average clock correction for each satellite visible to the master reference station by forming a linear combination of the master clock correction and the local clock corrections computed for the satellite.

A method for forming a smoothed refraction-corrected code measurement based on dual-frequency GPS pseudorange measurements and carrier-phase measurements taken from a satellite by a GPS receiver, comprising:

• for each of a series of measurement epochs preceding and including a current measurement epoch, forming a refraction-corrected code measurement based on the dual frequency pseudorange code measurements from the satellite and a refraction-corrected carrier-phase measurement based on the dual-frequency carrier phase measurements from the satellite;
• and
• smoothing the refraction-corrected code measurements with the refraction-corrected carrier phase measurements to obtain a smoothed refraction-corrected code measurement at the current measurement epoch,
• wherein smoothing the refraction-corrected code measurement includes forming projections of the smoothed refraction-corrected code measurements using changes in the carrier-phase measurements between two consecutive measurement epochs, and computing an expanding average of differences between the projections and the refraction-corrected code measurements over a series of measurement epochs.

A method for forming a smoothed refraction-corrected code measurement based on dual-frequency GPS pseudorange measurements and carrier-phase measurements taken from a satellite at a GPS receiver, comprising:

• forming at each of a series of measurement epochs and for each carrier signal frequency a linear combination of the dual-frequency carrier-phase measurements to match the ionospheric refraction effect on the corresponding pseudorange code measurement;
• forming a smoothed code measurement for each carrier signal frequency by smoothing the pseudorange code measurements with the matching linear combinations of the dual-frequency carrier-phase measurements;
• and
• combining the smoothed code measurements to form the smoothed refraction-corrected code measurement,
• wherein combining the smoothed code measurements to form the smoothed refraction-corrected code measurement includes forming projections of the smoothed refraction-corrected code measurements using changes in the carrier-phase measurements between two consecutive measurement epochs, and computing an expanding average of differences between the projections and the refraction-corrected code measurements over a series of measurement epochs.

A computer readable medium comprising computer executable program instructions that when executed cause a digital processing system to perform a method for generation GPS satellite clock corrections, the method comprising:

• obtaining dual-frequency pseudorange code measurements and carrier-phase measurements from a plurality of satellites;
• for each of the plurality of satellites, forming a smoothed refraction-corrected code measurement based on the dual-frequency pseudorange code measurements and carrier-phase measurements from the satellite, wherein the forming is performed for each of a series of measurement epochs preceding and including a current measurement epoch, forming the smoothed refraction-corrected code measurement at the current measurement epoch includes smoothing refraction-corrected code measurements with refraction-corrected carrier phase measurements, and wherein smoothing the refraction-corrected code measurement includes forming projections of the smoothed refraction-corrected code measurements using changes in the carrier-phase measurements between two consecutive measurement epochs and computing an expanding average of differences between the projections and the refraction-corrected code measurements over a series of measurement epochs;
• and
• computing clock corrections for the plurality of satellites based on the smoothed refraction-corrected code measurements.

A computer readable medium comprising computer executable program instructions that when executed cause a digital processing system to perform a method for generation satellite clock corrections for a wide-area GPS network having a plurality of reference stations including a master reference station and a plurality of local reference stations, the method comprising:

• for each reference station, obtaining a smoothed refraction-corrected code measurement for each satellite visible to the reference station formed using GPS measurements taken from the satellite at the reference station;
• computing a master clock correction for each satellite visible to the master reference station using the smoothed refraction-corrected code measurements for the master reference station;
• for each of the plurality of local reference stations, computing a local clock correction for each satellite common to the master reference station and the local reference station using smoothed refraction-corrected code measurements for the master reference station and for the local reference station;
• and
• computing an average clock correction for each satellite visible to the master reference station by forming a linear combination of the master clock correction and the local clock corrections computed for the satellite.