Ionosphere delay measurement using carrier phase

1. A method for compensating for distortion from a dispersive medium, comprising:

receiving a modulated radio-frequency (RF) signal that has propagated through said dispersive medium, wherein the modulated RF signal is received from a satellite source;

downconverting said modulated RF signal to produce a baseband signal, wherein the baseband signal preserves an upper sideband and a lower sideband present in the modulated RF signal;

tracking a first downconverted carrier phase corresponding to the upper sideband;

tracking a second downconverted carrier phase corresponding to the lower sideband, wherein at least one of the first tracked downconverted carrier phase or the second tracked downconverted carrier phase is used to determine a range measurement to the satellite source;

extracting a phase difference between said first downconverted carrier phase and said second downconverted carrier phase; and

determining a correction for the range measurement to the satellite source based at least in part on said extracted phase difference.

2. The method of claim 1 , wherein said modulated RF signal is received from a navigation satellite.

3. The method of claim 1 , wherein said modulated signal comprises a GPS M-code subcarrier signal, and wherein the upper sideband and the lower sideband correspond to the M-code subcarrier signal.

4. The method of claim 1 , wherein said modulated RF signal comprises a GPS L1 M-code subcarrier signal, and wherein the upper sideband and the lower sideband correspond to the M-code subcarrier signal.

5. The method of claim 1 , wherein said modulated RF signal comprises a GPS L2 M-code subcarrier signal, and wherein the upper sideband and the lower sideband correspond to the M-code subcarrier signal.

6. The method of claim 1 , wherein said modulated RF signal comprises a Galileo signal.

7. The method of claim 1 , wherein said dispersive medium comprises at least a portion of the earth's ionosphere.

8. The method of claim 1 , wherein said dispersive medium comprises a plasma.

9. The method of claim 1 , wherein said dispersive medium comprises a partially ionized medium.

10. The method of claim 1 , wherein determining the correction for the range measurement further comprises determining a total electron content for a signal path from the satellite source.

11. The method of claim 1 , further comprising, using said phase difference to correct a phase between said upper sideband and said lower sideband.

12. The method of claim 1 , further comprising, using said phase difference to correct a phase between said upper sideband and said lower sideband to condition said second upper sideband and said lower sideband for demodulation.

13. The method of claim 1 , further comprising, using said phase difference to adjust a phase of at least said upper sideband or said lower sideband such that after adjustment said upper sideband and said lower sideband are substantially in phase.

14. The method of claim 1 , further comprising, using said phase difference to adjust a phase of at least said upper sideband or said lower sideband such that after adjustment said upper sideband and said lower sideband are substantially out of phase.

15. The method of claim 1 , further comprising:

generating an expected phase difference between the upper sideband and the lower sideband;

comparing the expected phase difference to the extracted phase difference; and

detecting the presence of a spoofing signal in response to the comparison.

16. A receiver, comprising:

an antenna configured to receive a radio-frequency (RF) signal from a satellite source, wherein the RF signal has propagated through a dispersive medium, wherein the RF signal is modulated;

a downconverter configured to downconvert said radio-frequency signal to produce a baseband signal, wherein the baseband signal has an upper sideband and a lower sideband;

a first tracker configured to track a first downconverted carrier phase corresponding to the upper sideband;

a second tracker configured to track a second downconverted carrier phase corresponding to the lower sideband, wherein at least one of the first tracked downconverted carrier phase or the second tracked downconverted carrier phase is used to determine a range measurement to the satellite source;

a phase comparator configured to evaluate a phase difference between said first downconverted carrier phase and said second downconverted carrier phase; and

an estimator configured to determine a correction for the range measurement to the satellite source based at least in part on said extracted phase difference.

17. The receiver of claim 16 , wherein said radio-frequency signal comprises a GPS M-code subcarrier signal, and wherein the upper sideband and the lower sideband correspond to the M-code subcarrier signal.

18. The receiver of claim 16 , wherein said radio-frequency signal comprises a GPS L1 M-code subcarrier signal, and wherein the upper sideband and the lower sideband correspond to the M-code subcarrier signal.

19. The receiver of claim 16 , wherein said radio-frequency signal comprises a GPS L2 M-code subcarrier signal, and wherein the upper sideband and the lower sideband correspond to the M-code subcarrier signal.

20. The receiver of claim 16 , wherein said radio-frequency signal comprises a Galileo signal.

21. The receiver of claim 16 , wherein said dispersive medium comprises at least a portion of the earth's ionosphere.

22. The receiver of claim 16 , wherein said dispersive medium comprises a plasma.

23. The receiver of claim 16 , wherein said dispersive medium comprises a partially ionized medium.

24. The receiver of claim 16 , wherein the estimator is further configured to determine a total electron content of a portion of an ionosphere for a signal path from the satellite source.

25. The receiver of claim 16 , further comprising, a phase shifter, said receiver configured to provide said phase difference to said phase shifter, said phase shifter configured to correct a phase between said upper sideband and said lower sideband.

26. The receiver of claim 16 , further comprising a phase shifter, said receiver configured to provide said phase difference to said phase shifter, said phase shifter configured to correct a phase between said upper sideband and said lower sideband to condition said upper sideband and said lower sideband for demodulation.

27. The receiver of claim 16 , further comprising, a phase shifter, said receiver configured to provide said phase difference to said phase shifter, said phase shifter configured to adjust a phase of at least said upper sideband or said lower sideband such that after adjustment said upper sideband and said lower sideband are substantially in phase.

28. The receiver of claim 16 , further comprising, a phase shifter, said receiver configured to provide said phase difference to said phase shifter, said phase shifter configured to adjust a phase of at least said upper sideband or said lower sideband such that after adjustment said upper sideband and said lower sideband are substantially out of phase.

29. The receiver of claim 16 , further comprising:

a phase shifter, said receiver configured to provide said phase difference to said phase shifter, said phase shifter configured to correct a phase between said upper sideband and said lower sideband to produce a phase-corrected signal; and

a demodulator configured to demodulate said phase-corrected signal.

30. The receiver of claim 16 , further configured to estimate ionospheric properties using signals received from a plurality of satellites.

31. The receiver of claim 16 , wherein said radio-frequency signal is received from a navigation satellite.