Method and apparatus for smoothing code measurements in a global positioning system receiver

A method for smoothing global positioning system (GPS) code measurements of pseudorange with carrier phase measurements over an extended time interval, the method comprising the steps of:

• obtaining pseudorange code measurements and integrated carrier phase measurements in a GPS receiver;
• subtracting integrated carrier phase measurements from pseudorange code measurements to remove Doppler effects and obtain code offset measurements;
• removing signal delay ionospheric effects from the code offset measurements;
• filtering the code offset measurements after removal of the ionospheric effects, over an extended time interval to remove the effect of errors that affect pseudorange measurements more than integrated carrier phase measurements;
• and
• adding back to the filtered code offset measurements the integrated carrier phase measurements, to obtain smoothed pseudorange code measurements.

A method for differential position determination at a remote global positioning system (GPS) receiver, using a reference GPS receiver of which the position is known, the method comprising the steps of:

• in the reference receiver, obtaining pseudorange code measurements and integrated carrier phase measurements, subtracting the carrier phase measurements from the pseudorange code measurements to obtain code offset measurements, removing signal delay ionospheric effects from the code offset measurements, filtering the resulting code offset measurements to obtain smoothed code offset measurements, adding back the carrier phase measurements to obtain smoothed pseudorange code measurements, computing range measurements from the known position of the receiver and known orbital parameters of satellites from which signals are being received, and subtracting the computed range measurements from the smoothed pseudorange code measurements, to obtain range corrections;
• transmitting from the reference receiver to the remote receiver the code offset measurements prior to smoothing, and at least one set of measurements pertaining to smoothed range corrections;
• in the remote receiver, obtaining pseudorange code measurements and integrated carrier phase measurements, subtracting the carrier phase measurements from the pseudorange code measurements to obtain code offset measurements, removing signal delay ionospheric effects by subtracting the code offset measurements received from the reference receiver, filtering the resulting code offset measurements to obtain smoothed code offset measurements, adding back the carrier phase measurements to obtain smoothed pseudorange code measurements, and then applying range corrections derived in part from the at least one set of measurements pertaining to smoothed range corrections, to derive corrected range measurements.

A method for differential position determination at a remote global positioning system (GPS) receiver, using a reference GPS receiver of which the position is known, the method comprising the steps of:

• in the reference receiver, obtaining pseudorange code measurements and integrated carrier phase measurements;
• transmitting to the remote receiver at least two sets of measurements selected from the pseudorange code measurements, the integrated carrier phase measurements, corrections to the pseudorange code measurements, corrections to the integrated carrier measurements, and the difference between the pseudorange code measurements and the integrated carrier phase measurements;
• and
• in the remote receiver, locally obtaining pseudorange code measurements and integrated carrier phase measurements, then processing the locally obtained measurements using the measurements received from the reference receiver, to derive a set of measurements substantially free of signal delay ionospheric effects and Doppler effects, filtering this derived set of measurements to remove noise effects, and restoring the Doppler effect to provide a smoothed and corrected set of pseudorange code measurements.

For use in a global positioning system (GPS) receiver having a single frequency of operation, apparatus for smoothing GPS code measurements of pseudorange with carrier phase measurements over an extended time interval without distortion due to divergence between code measurements and carrier measurements, the apparatus comprising:

• means for obtaining pseudorange code measurements and integrated carrier phase measurements in a single-frequency GPS receiver;
• means for deriving from the pseudorange code measurements and the integrated carrier phase measurements a composite set of measurements that is substantially free of Doppler effects and signal delay ionospheric effects;
• means for filtering the composite set of measurements over an extended time interval to remove errors that affect pseudorange measurements more than integrated carrier phase measurements;
• and
• means for replacing Doppler effects in the filtered composite set of measurements, to obtain smoothed pseudorange code measurements.

Apparatus for smoothing global positioning system (GPS) code measurements of pseudorange with carrier phase measurements over an extended time interval, the apparatus comprising:

• means for obtaining pseudorange code measurements and integrated carrier phase measurements in a GPS receiver;
• means for subtracting integrated carrier phase measurements from pseudorange code measurements to remove Doppler effects and obtain code offset measurements;
• means for removing signal delay ionospheric effects from the code offset measurements;
• means for filtering the code offset measurements after removal of the signal delay ionospheric effects, over an extended time interval to remove the effect of errors that affect pseudorange measurements more than integrated carrier phase measurements;
• and
• means for adding back to the filtered code offset measurements the integrated carrier phase measurements, to obtain smoothed pseudorange code measurements.

Apparatus for differential position determination at a remote global positioning system (GPS) receiver, using a reference GPS receiver of which the position is known, the apparatus comprising:

• a reference receiver, including means for obtaining pseudorange code measurements and integrated carrier phase measurements, means for subtracting the carrier phase measurements from the pseudorange code measurements to obtain code offset measurements, means for removing signal delay ionospheric effects from the code offset measurements, means for filtering the resulting code offset measurements to obtain smoothed code offset measurements, means for adding back the carrier phase measurements to obtain smoothed pseudorange code measurements, means for computing range measurements from the known position of the receiver and known orbital parameters of satellites from which signals are being received, and means for subtracting the computed range measurements from the smoothed pseudorange code measurements, to obtain range corrections;
• means for transmitting from the reference receiver to a remote receiver the code offset measurements prior to smoothing, and at least one set of measurements pertaining to smoothed range corrections;
• a remote receiver, including means for obtaining pseudorange code measurements and integrated carrier phase measurements, means for subtracting the carrier phase measurements from the pseudorange code measurements to obtain code offset measurements, means for removing signal delay ionospheric effects by subtracting the code offset measurements received from the reference receiver, means for filtering the resulting code offset measurements to obtain smoothed code offset measurements, means for adding back the carrier phase measurements to obtain smoothed pseudorange code measurements, and means for applying range corrections derived in part from the at least one set of measurements pertaining to smoothed range corrections, to derive corrected range measurements.

Apparatus for differential position determination at a remote global positioning system (GPS) receiver, using a reference GPS receiver of which the position is known, the apparatus comprising:

• a reference receiver, including means for obtaining pseudorange code measurements and integrated carrier phase measurements;
• means for transmitting to a remote receiver at least two sets of measurements selected from the pseudorange code measurements, the integrated carrier phase measurements, corrections to the pseudorange code measurements, corrections to the integrated carrier measurements, and the difference between the pseudorange code measurements and the integrated carrier phase measurements;
• and
• a remote receiver, including means for obtaining pseudorange code measurements and integrated carrier phase measurements, means for processing the locally obtained measurements using the measurements received from the reference receiver, to derive a set of measurements substantially free of signal delay ionospheric effects and Doppler effects, means for filtering this derived set of measurements to remove noise effects, and means for restoring the Doppler effect to provide a smoothed and corrected set of pseudorange code measurements.