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

Claim 2

For use in a global positioning system (GPS) receiver having a single frequency of operation, a method 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 method comprising the steps of: obtaining pseudorange code measurements and integrated carrier phase measurements in a single-frequency GPS receiver; 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 ionospheric effects; 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 replacing Doppler effects in the filtered composite set of measurements, to obtain smoothed pseudorange code measurements.

Claim 3

A method as defined in claim 1, wherein the step of deriving a composite set of measurements includes: receiving pseudorange code corrections from a reference receiver; applying the pseudorange code corrections to the pseudorange code measurements, to obtain corrected pseudorange code measurements virtually free of ionospheric errors; receiving carrier phase corrections from the reference receiver; applying the carrier phase corrections to the pseudorange code measurements, to obtain corrected carrier phase measurements virtually free of ionospheric errors; and subtracting the corrected carrier phase measurements from the corrected pseudorange code measurements, to obtain the composite set of measurements without ionospheric or Doppler effects.

Claim 4

A method as defined in claim 1, wherein the step of deriving a composite set of measurements includes: subtracting the carrier phase measurements from the pseudorange code measurements, to obtain code offset measurements substantially free of Doppler effects; and subtracting ionospheric error values from the code offset measurements, to obtain the composite set of measurements substantially free of ionospheric and Doppler effects.

Claim 7

A method as defined in claim 4, wherein: the step of removing ionospheric effects from the code offset measurements includes applying a correction derived from independent ionospheric measurements.

Claim 8

A method as defined in claim 4, wherein: the step of removing ionospheric effects from the code offset measurements includes applying a correction derived from ionospheric model data received with GPS signals.

Claim 11

A method as defined in claim 7, wherein: in the reference receiver, the step of removing ionospheric effects from the code offset measurements includes applying a correction derived from independent ionospheric measurements.

Claim 12

A method as defined in claim 7, wherein: the step of removing ionospheric effects from the code offset measurements includes applying a correction derived from ionospheric model data received with GPS signals.

Claim 13

A method as defined in claim 7, wherein: the step of transmitting at least one set of measurements pertaining to smoothed range corrections includes transmitting smoothed code offset measurements and transmitting range corrections; and in the remote receiver, the step of applying range corrections includes subtracting the smoothed code offset measurements received from the reference receiver from the range corrections transmitted from the reference receiver, subtracting the resulting range errors from estimated ranges computed in the remote receiver, and subtracting the result of the latter subtraction from the smoothed code offset measurements generated in the remote receiver, to obtain the corrected range measurements.

Claim 16

A method as defined in claim 11, wherein: in the reference receiver, the method further includes computing theoretical pseudorange values and theoretical carrier phase values using the reference receiver's known position and known information about satellite orbits, and computing corrections for the pseudorange code measurements and the carrier phase measurements; the step of transmitting to the remote receiver includes transmitting the corrections for the pseudorange code measurements and the carrier phase measurements; and in the remote receiver, the step of processing the locally obtained measurements includes applying the corrections transmitted from the reference receiver, to obtain corrected pseudorange code measurements and corrected carrier phase measurements that are virtually free of ionospheric effects, then subtracting the corrected carrier phase measurements from the corrected pseudorange code measurements, to obtain the set of measurements for filtering.

Claim 17

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 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.

Claim 18

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 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.

Claim 19

Apparatus as defined in claim 13, wherein the means for deriving a composite set of measurements includes: means for receiving pseudorange code corrections from a reference receiver; means for applying the pseudorange code corrections to the pseudorange code measurements, to obtain corrected pseudorange code measurements virtually free of ionospheric errors; means for receiving carrier phase corrections from the reference receiver; means for applying the carrier phase corrections to the pseudorange code measurements, to obtain corrected carrier phase measurements virtually free of ionospheric errors; and means for subtracting the corrected carrier phase measurements from the corrected pseudorange code measurements, to obtain the composite set of measurements without ionospheric or Doppler effects.

Claim 20

Apparatus as defined in claim 13, wherein the means for deriving a composite set of measurements includes: means for subtracting the carrier phase measurements from the pseudorange code measurements, to obtain code offset measurements substantially free of Doppler effects; and means for subtracting ionospheric error values from the code offset measurements, to obtain the composite set of measurements substantially free of ionospheric and Doppler effects.

Claim 21

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 ionospheric effects from the code offset measurements; means for 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 means for adding back to the filtered code offset measurements the integrated carrier phase measurements, to obtain smoothed pseudorange code measurements.

Claim 22

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 ionospheric effects from the code offset measurements; means for 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 means for adding back to the filtered code offset measurements the integrated carrier phase measurements, to obtain smoothed pseudorange code measurements.

Claim 23

Apparatus as defined in claim 16, wherein: the means for removing ionospheric effects from the code offset measurements includes means for applying a correction derived from independent ionospheric measurements.

Claim 24

Apparatus as defined in claim 16, wherein: the means for removing ionospheric effects from the code offset measurements includes means for applying a correction derived from ionospheric model data received with GPS signals.

Claim 25

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 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 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.

Claim 26

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 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 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.

Claim 27

Apparatus as defined in claim 19, wherein: in the reference receiver, the means for removing ionospheric effects from the code offset measurements includes means for applying a correction derived from independent ionospheric measurements.

Claim 28

Apparatus as defined in claim 19, wherein: in the reference receiver, the means for removing ionospheric effects from the code offset measurements includes applying a correction derived from ionospheric model data received with GPS signals.

Claim 29

Apparatus as defined in claim 19, wherein: the means for transmitting at least one set of measurements pertaining to smoothed range corrections includes means for transmitting smoothed code offset measurements and transmitting range corrections; and in the remote receiver, the means for applying range corrections includes means for subtracting the smoothed code offset measurements received from the reference receiver from the range corrections transmitted from the reference receiver, means for subtracting the resulting range errors from estimated ranges computed in the remote receiver, and means for subtracting the result of the latter subtraction from the smoothed code offset measurements generated in the remote receiver, to obtain the corrected range measurements.

Claim 30

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 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.

Claim 31

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 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.

Claim 32

Apparatus as defined in claim 23, wherein: the reference receiver further includes means for computing theoretical pseudorange values and theoretical carrier phase values using the reference receiver's known position and known information about satellite orbits, and means for computing corrections for the pseudorange code measurements and the carrier phase measurements; the means for transmitting to the remote receiver includes means for transmitting the corrections for the pseudorange code measurements and the carrier phase measurements; and in the remote receiver, the means for processing the locally obtained measurements includes means for applying the corrections transmitted from the reference receiver, to obtain corrected pseudorange code measurements and corrected carrier phase measurements that are virtually free of ionospheric effects, and means for subtracting the corrected carrier phase measurements from the corrected pseudorange code measurements, to obtain the set of measurements for filtering.