Reducing satellite signal interference in a global positioning system receiver

• US 6,236,354 B1
• Filed: 07/02/1998
• Issued: 05/22/2001
• Est. Priority Date: 07/02/1998
• Status: Expired due to Term

• Current Assignee: Alliance For Sustainable Energy LLC
• Original Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Inventors: Krasner, Norman F.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US09/109,112
• Time in Patent Office: 1,055 Days
• Field of Search: 342/357.06, 342/357.1, 342/357.12, 342/357.15, 701/213
• US Class Current: 342/357.59
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
• CPC Class Codes: G01S 19/246 involving long acquisition integration times, extended snapshots of signals or methods specifically directed towards weak signal acquisition
• CPC Class Codes: G01S 5/0036 of measured values, i.e. measurement on mobile and position calculation on base station
• CPC Class Codes: G01S 5/0054 of actual mobile position, i.e. position calculation on base station
• CPC Class Codes: H04B 7/18513 Transmission in a satellite or space-based system

Abstract

A method and apparatus is disclosed for reducing cross-interference between received satellite signals in a satellite positioning system receiver. A satellite positioning receiver receives satellite signals from a plurality of satellites. Spurious signals when processing a weak received satellite signal due to interference by a stronger received signal are reduced by estimating certain characteristics of the stronger signal, creating an interference waveform based on these estimated characteristics, and subtracting this interference waveform from a set of correlation outputs for the weaker signal to remove the interference effects of the stronger signal. Alternatively, a subset of these correlation outputs are ignored where the interference waveform produces strong spurious signals.

Claims

1. A method for reducing satellite signal cross-interference in a satellite positioning system receiver, said method comprising the steps of:

receiving as an input waveform a first signal and a second signal from respective satellites of a plurality of satellite positioning system satellites, wherein said first signal is stronger than said second signal;

estimating characteristics of said first signal to form estimated data;

constructing an interference waveform using said estimated data and a hypothesized carrier frequency of said second signal and pseudorandom codes corresponding to said first signal and said second signal;

performing tests for times of arrival of said second signal to produce a first output waveform;

selecting a portion of said interference waveform; and

subtracting said portion of said interference waveform from said first output waveform to produce a second output waveform.

2. The method of claim 1 wherein said characteristics of said first signal comprise a time-of-arrival, amplitude, and carrier frequency of said first signal.

3. The method of claim 2 wherein said step of performing tests for times of arrival of said second signal further comprises the step of performing correlation operations on said second signal to produce correlated output data.

4. The method of claim 2 wherein said step of performing tests for times of arrival of said second signal further comprises the step of performing a matched filtering operation on said second signal to produce matched filtered out put data.

5. The method of claim 2 wherein said portion of said interference waveform is selected such that the step of subtracting said portion of said interference waveform from said first output waveform is operable to reduce an interference component due to said first signal upon said second signal.

6. The method of claim 5 further comprising the step of processing data comprising said second output waveform to acquire said second signal.

43. The method of claim 2 wherein said steps of estimating said characteristics, constructing said interference waveform, performing said tests, selecting said portion of said interference waveform, and subtracting said portion of said interference waveform are performed in a remote location separate from said satellite positioning system receiver, and wherein data is transmitted from said satellite positioning system receiver to said remote location to permit said steps to be performed.

7. A method for reducing satellite signal cross-interference in a satellite positioning system receiver, said method comprising the steps of:

receiving as an input waveform a first signal and a second signal from respective satellites of a plurality of satellite positioning system satellites, wherein said first signal is stronger than said second signal;

estimating characteristics of said first signal to form estimated data;

constructing an interference waveform using said estimated data; and

subtracting said interference waveform from said first input waveform to produce an output waveform.

8. The method of claim 7 wherein said characteristics of said first signal comprise a time-of-arrival, amplitude, carrier frequency, and phase of said first signal.

9. The method of claim 8 wherein said interference waveform is selected such that the step of subtracting interference waveform from said input waveform is operable to reduce an interference component due to said first signal upon said second signal.

10. The method of claim 9 further comprising the step of processing said output signal in a correlation system to determine pseudoranges for said second signal.

11. The method of claim 9 further comprising the step of processing said output signal in a matched filtering system to determine pseudoranges for said second signal.

12. The method of claim 9 further comprising the step of processing data comprising said output waveform to search for and acquire said second signal.

44. The method of claim 8 wherein said steps of estimating said characteristics, constructing said interference waveform, and subtracting said interference waveform are performed in a remote location separate from said satellite positioning system receiver, and wherein data is transmitted from said satellite positioning system receiver to said remote location to permit said steps to be performed.

13. A method for reducing satellite signal cross-interference in a satellite positioning system receiver, said method comprising the steps of:

receiving as an input waveform a first signal and a second signal from respective satellites of a plurality of satellite positioning system satellites, wherein said first signal is stronger than said second signal;

estimating characteristics of said first signal to form estimated data;

constructing an interference waveform using said estimated data and a hypothesized carrier frequency of said second signal and a first pseudorandom code corresponding to said first signal and a second pseudorandom code corresponding to said second signal;

performing tests for times of arrival of said second signal to produce an output waveform; and

discarding portions of said output waveform for which said interference waveform is above a predetermined threshold.

14. The method of claim 13 wherein said characteristics of said first signal comprise a time-of-arrival, amplitude, and carrier frequency of said first signal.

15. The method of claim 14 wherein said step of performing tests for times of arrival of said second signal further comprises the step of performing correlation operations on said second signal to produce correlated output data.

16. The method of claim 14 wherein said step of performing tests for times of arrival of said second signal further comprises the step of performing a matched filtering operations on said second signal to produce matched filtered output data.

17. The method of claim 14 further comprising the step of processing data comprising said output waveform to search for and acquire said second signal.

45. The method of claim 14 wherein said steps of estimating said characteristics, constructing said interference waveform, performing said tests, and discarding said portions of said output waveform are performed in a remote location separate from said satellite positioning system receiver, and wherein data is transmitted from said satellite positioning system receiver to said remote location to permit said steps to be performed.

18. A method for reducing satellite signal cross-interference in a satellite positioning system receiver, said method comprising the steps of:

receiving as an input waveform a first signal and a second signal from respective satellites of a plurality of satellite positioning system satellites, wherein said first signal is stronger than said second signal;

estimating characteristics of said first signal to form estimated data;

detecting the presence of an interference component in said input signal by processing said estimated data and a hypothesized carrier frequency of said second signal;

determining the width of a peak of a signal produced by cross-correlations of said first signal and the PN code of said second signal if said interference component is detected;

comparing said width of said peak with a predetermined threshold;

performing tests for times of arrival of said second signal to produce an output waveform; and

deleting said peak from said output waveform if said width of said peak exceeds said predetermined threshold.

19. The method of claim 18 wherein said characteristics of said first signal comprise an amplitude and carrier frequency of said first signal.

20. The method of claim 19 wherein said step of performing tests for times of arrival of said second signal further comprises the step of performing correlation operations on said second signal to produce correlated output data.

21. The method of claim 19 wherein said step of performing tests for times of arrival of said second signal further comprises the step of performing a matched filtering operation on said second signal to produce matched filtered output data.

22. The method of claim 21 further comprising the step of processing data comprising said output waveform to search for and acquire said second signal.

46. The method of claim 19 wherein said steps of estimating said characteristics, constructing said interference waveform, detecting the presence of said interference component, determining the width of said peak, comparing the width of said peak, performing said tests, and deleting said peak from said output waveform are performed in a remote location separate from said satellite positioning system receiver, and wherein data is transmitted from said satellite positioning system receiver to said remote location to permit said steps to be performed.

47. The method of claim 46 further comprising the steps of:

estimating a signal to noise ratio for said peak at said satellite positioning system receiver; and

transmitting the estimated signal to noise ratio to said remote location remote from said satellite positioning system receiver.

23. A method for reducing satellite signal cross-interference in a satellite positioning system receiver, said method comprising the steps of:

receiving as an input waveform a first signal and a second signal from respective satellites of a plurality of satellite positioning system satellites, wherein said first signal is stronger than said second signal;

performing tests for times of arrival of said second signal to produce an output waveform;

subtracting a mean noise level from said output waveform to produce a modified output waveform;

establishing a detection threshold by multiplying a first constant by a root mean squared level of said modified output waveform; and

modifying said detection threshold by multiplying said detection threshold by a first value to produce a modified detection threshold.

24. The method of claim 23 wherein said first value comprises the ratio of the root mean squared value of positive components of said modified output divided by the root mean squared value of negative components of said modified output.

25. The method of claim 24 further comprising the steps of:

comparing said modified output waveform with said modified detection threshold; and

signaling a detection of a pseudorandom noise signal for said second signal if a component of said modified output exceeds said modified detection threshold.

26. The method of claim 25 wherein said tests for times of arrival of said second signal is a correlation operation.

27. The method of claim 26 wherein said tests for times of arrival of said second signal is a matched filtering operation.

48. The method of claim 23 wherein said steps of performing said tests, subtracting said mean noise level, establishing said detection threshold, and modifying said detection threshold are performed in a remote location separate from said satellite positioning system receiver, and wherein data is transmitted from said satellite positioning system receiver to said remote location to permit said steps to be performed.

28. An apparatus comprising:

an input circuit operable to receive satellite positioning system signals from a plurality of satellite positioning system satellites, and wherein a first received signal is stronger than a second received signal;

a processor coupled to said input circuit, said processor operable to estimate characteristics of said first signal;

construct an interference waveform based on the estimated characteristics;

perform tests for times of arrival of said second signal to produce an output waveform; and

subtract said interference waveform from said output waveform to remove interference effects of said first signal from said output waveform.

29. The apparatus of claim 28 further comprising an output circuit receiver circuit coupled to said processor, said output circuit comprising a display operable to display location information of said apparatus.

30. The apparatus of claim 28 further comprising an output circuit receiver circuit coupled to said processor, said output circuit comprising a communication transceiver operable to transmit pseudorange information corresponding to satellites of said plurality of satellites to a remote basestation over a communication link.

31. An apparatus comprising:

an input circuit operable to receive satellite positioning system signals from a plurality of satellite positioning system satellites, and wherein a first received signal is stronger than a second received signal;

a processor coupled to said input circuit, said processor operable to estimate characteristics of said first signal;

construct an interference waveform based on the estimated characteristics; and

subtract said interference waveform from the received satellite positioning system signals to remove interference effects of said first signal from said received signals.

32. The apparatus of claim 31 further comprising an output circuit receiver circuit coupled to said processor, said output circuit comprising a display operable to display location information of said apparatus.

33. The apparatus of claim 31 further comprising an output circuit receiver circuit coupled to said processor, said output circuit comprising a communication transceiver operable to transmit pseudorange information corresponding to satellites of said plurality of satellites to a remote basestation over a communication link.

34. An apparatus comprising:

an input circuit operable to receive satellite positioning system signals from a plurality of satellite positioning system satellites, and wherein a first received signal is stronger than a second received signal;

a processor coupled to said input circuit, said processor operable to estimate characteristics of said first signal;

construct an interference waveform based on the estimated characteristics and a first locally generated code corresponding to said first signal and a second locally generated code corresponding to said second signal;

perform tests for times of arrival of said second signal to produce an output waveform; and

discard portions of said output waveform for which said interference waveform is above a predetermined threshold.

35. The apparatus of claim 34 further comprising an output circuit receiver circuit coupled to said processor, said output circuit comprising a display operable to display location information of said apparatus.

36. The apparatus of claim 34 further comprising an output circuit receiver circuit coupled to said processor, said output circuit comprising a communication transceiver operable to transmit pseudorange information corresponding to satellites of said plurality of satellites to a remote basestation over a communication link.

37. An apparatus comprising:

an input circuit operable to receive satellite positioning system signals from a plurality of satellite positioning system satellites, and wherein a first received signal is stronger than a second received signal;

a processor coupled to said input circuit, said processor operable to estimate characteristics of said first signal;

determine the possibility of interference from said first signal with said second signal using the estimated characteristics and a characteristic of said second signal;

perform tests for a time-of-arrival of said second signal to produce an output waveform;

compare the width of a peak in said output waveform with a predetermined threshold; and

discard said peak from further processing if said width exceeds said predetermined threshold, and the possibility of interference from said first signal with said second signal is affirmative.

38. The apparatus of claim 37 further comprising an output circuit receiver circuit coupled to said processor, said output circuit comprising a display operable to display location information of said apparatus.

39. The apparatus of claim 37 further comprising an output circuit receiver circuit coupled to said processor, said output circuit comprising a communication transceiver operable to transmit pseudorange information corresponding to satellites of said plurality of satellites to a remote basestation over a communication link.

40. An apparatus comprising:

an input circuit operable to receive satellite positioning system signals from a plurality of satellite positioning system satellites, and wherein a first received signal is stronger than a second received signal;

a processor coupled to said input circuit, said processor operable to perform tests for times of arrival of said second signal to produce an output waveform;

subtract a mean noise level from said output waveform to form a modified output waveform;

establish a detection threshold based on a root mean squared value of data in said output waveform;

compare said modified output waveform with said detection threshold; and

signal a detection if a portion of said modified output waveform exceeds said detection threshold.

41. The apparatus of claim 40 further comprising an output circuit receiver circuit coupled to said processor, said output circuit comprising a display operable to display location information of said apparatus.

42. The apparatus of claim 40 further comprising an output circuit receiver circuit coupled to said processor, said output circuit comprising a communication transceiver operable to transmit pseudorange information corresponding to satellites of said plurality of satellites to a remote basestation over a communication link.

49. A method for processing satellite positioning system (SPS) signals transmitted from a first satellite, said method comprising the steps of:

receiving said SPS signals at a mobile SPS receiver;

determining at least one signal-to-noise ratio for at least one of said SPS signals; and

transmitting said at least one signal-to-noise ratio to a remote processing system.

50. The method of claim 49 wherein said remote processing system calculates a position based at least in part on said at least one signal-to-noise ratio.

51. The method of claim 50 wherein said remote processing system uses said at least one signal-to-noise ratio to reduce cross-talk interference from SPS signals transmitted from a second satellite.

52. A method for processing satellite positioning system (SPS) signals transmitted from a first satellite, said method comprising the steps of:

receiving said SPS signals at a mobile SPS receiver;

determining at least one peak width for at least one of said SPS signals; and

transmitting said at least one peak width to a remote processing system.

53. The method of claim 52 wherein said remote processing system calculates a position based at least in part on said at least one peak width.

54. The method of claim 53 wherein said remote processing system uses said at least one peak width to reduce cross-talk interference from SPS signals transmitted from a second satellite.