Method for using three GPS frequencies to resolve carrier-phase integer ambiguities

1. A method for obtaining an ambiguity-resolved, refraction-corrected GPS carrier-phase measurement, comprising:

obtaining carrier-phase measurements on three carrier frequencies;

forming at least two wide-lane carrier phase measurements based on the carrier-phase measurements on the three carrier frequencies;

resolving whole-cycle ambiguities in the wide-lane carrier-phase measurements; and

using the ambiguity-resolved wide-lane measurements to form the ambiguity-resolved, refraction-corrected GPS carrier-phase measurement.

2. The method of claim 1 wherein the three GPS frequencies include a first frequency, a second frequency frequency, and a third frequency, the wide-lane carrier phase measurements include a first wide-lane carrier-phase measurement formed using carrier-phase measurements on the first and the second frequencies and a second wide-lane carrier-phase measurement formed using carrier-phase measurements on the second and the third frequencies, and the ambiguity-resolved, refraction-corrected GPS carrier-phase measurement comprises a difference between the first wide-lane measurement and a multiple of the second wide-lane measurement.

3. The method of claim 1 wherein a ionospheric refraction error in the first wide-lane measurement is approximately equal to the ionospheric refraction error in the multiple of the second wide-lane measurement.

4. The method of claim 1 wherein the whole-cycle ambiguity in each wide-lane carrier-phase measurement is resolved based on a frequency-weighted average of corresponding GPS code measurements, an error caused by ionospheric refraction in the frequency-weighted average matching an error caused by ionospheric refraction in the wide-lane carrier-phase measurement.

5. A method for generating carrier-phase measurement, comprising:

forming a first composite measurement using GPS carrier-phase measurements on three GPS frequencies;

forming a second composite measurement using GPS carrier-phase measurements on at least two GPS carrier frequencies; and

smoothing the first composite measurement with the second composite measurement.

6. The method of claim 5 wherein the first composite measurement is a linear combination of the GPS carrier-phase measurements on the three GPS carrier frequencies.

7. The method of claim 5 wherein the first composite measurement is ambiguity-resolved and forming the first composite measurement comprises:

obtaining carrier-phase measurements on the three frequencies;

forming at least two wide-lane carrier phase measurements based on the carrier-phase measurements on the three frequencies; and

resolving whole-cycle ambiguities in the wide-lane carrier-phase measurements;

using the ambiguity-resolved wide-lane measurements to form the first composite measurement.

8. The method of claim 7 wherein the whole-cycle ambiguity in each wide-lane carrier-phase measurement is resolved based on a frequency-weighted average of corresponding GPS code measurements, an error caused by ionospheric refraction in the frequency-weighted average matching an error caused by ionospheric refraction in the wide-lane carrier-phase measurement.

9. The method of claim 5 wherein the second composite measurement is formed to have a small multi-path noise therein.

10. The method of claim 5 wherein the second composite measurement is formed using carrier-phase measurements on all of the three frequencies.

11. The method of claim 5 wherein the second composite measurement includes unresolved whole-cycle ambiguities.

12. The method of claim 5 wherein the second composite measurement has a wavelength of about 10.8 centimeters.

13. The method of claim 12 wherein the second composite measurement has a noise level of about 2.7 centimeters assuming equal phase-noise in each of the carrier-phase measurements on the three frequencies.

14. The method of claim 5 wherein the first and the second composite measurements are scaled by there respective wavelengths and wherein smoothing the first composite measurement with the second composite measurement comprises:

computing an offset between the first composite measurement and the second composite measurement at each of a plurality of measurement epochs;

smoothing the offset in an expanding average over the plurality of measurement epochs; and

adding the smoothed offset to the second composite measurement to obtain an ambiguity-resolved, refraction-corrected, and noise reduced GPS carrier-phase measurement.

15. A positioning or navigation system, comprising:

a GPS receiver configured to obtain GPS code and carrier-phase measurements based on signals from a plurality of satellites in view of the GPS receiver, the signals being transmitted in three different carrier frequencies;

a computer system coupled to the GPS receiver, the computer system includes a processor and a memory coupled to the process, the memory storing therein program instructions, the program instructions comprising:

instructions for forming a first composite measurement using GPS carrier-phase measurements on the three carrier GPS frequencies;

instructions for forming a second composite measurement using GPS carrier-phase measurements on at least two GPS carrier frequencies; and

instructions for smoothing the first composite measurement with the second composite measurement.

16. The positioning system of claim 15 , wherein the instructions for forming the first composite measurement comprise:

instructions for forming at least two wide-lane carrier phase measurements based on the carrier-phase measurements on the three carrier frequencies;

instructions for resolving whole-cycle ambiguities in the wide-lane carrier-phase measurements; and

instructions for using the ambiguity-resolved wide-lane measurements to form the first composite measurement.

17. The positioning system of claim 15 wherein the second composite measurement is formed to have a small multi-path noise therein.

18. The positioning system of claim 15 wherein the second composite measurement is formed using carrier-phase measurements on all of the three frequencies.

19. The positioning system of claim 15 wherein the second composite measurement includes unresolved whole-cycle ambiguities.

20. The positioning system of claim 15 wherein the instructions for smoothing the first composite measurement with the second composite measurement comprise:

instructions for computing an offset between the first composite measurement and the second composite measurement at each of a plurality of measurement epochs;

instructions for smoothing the offset in an expanding average over the plurality of measurement epochs; and

instructions for adding the smoothed offset to the second composite measurement to obtain an ambiguity-resolved, refraction-corrected, and noise reduced GPS carrier-phase measurement.