Continuous wave interference rejection for reconstructed carrier receivers

• US 4,860,018 A
• Filed: 08/11/1986
• Issued: 08/22/1989
• Est. Priority Date: 03/01/1982
• Status: Expired due to Term

• Current Assignee: Western Atlas International Incorporated (Northrop Grumman Corporation)
• Original Assignee: Western Atlas International Incorporated (Northrop Grumman Corporation)
• Inventors: Counselman, III, Charles C.
• Primary Examiner(s): Blum, Theodore M.
• Assistant Examiner(s): Sotomayor, John B.
• Application Number:
  US06/895,151
• Time in Patent Office: 1,107 Days
• Field of Search: 342/357, 342/352, 342/450, 342/451, 375/1, 370/104, 370/121
• US Class Current: 342/357.48
• CPC Class Codes: G01C 15/00 Surveying instruments or accessories not provided for in groups G01C1/00 - G01C13/00
• 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 19/44 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method

Abstract

System and method are disclosed for determining position related data from spread spectrum signals using reconstructed carrier receivers with continuous wave interference rejection. The spread spectrum signals are collected at a mark with a substantially omni-directional antenna and continuous wave interference is then rejected at or near a selected frequency. The spread spectrum signals are then reconstructed to provide a continuous wave component at that frequency form which the position data may be derived. The data is derived without interference because the potentially interfering signals, if present, have been rejected before the components were reconstructed.

Claims

1. A system for deriving position related data from signals modulated by mutually orthogonal, spectrum spreading codes, comprising:

antenna means for receiving a composite of signals including spread spectrum signals and potentially interfering continuous wave components;

filter means for rejecting the continuous wave components related to a selected frequency from the composite;

means for reconstructing at least one continuous wave component related to the selected frequency from the filtered spread spectrum components; and

means for deriving said position related data from the reconstructed component.

2. The system of claim 1 wherein the spread spectrum signals are transmitted concurrently with the same frequencies by each of a plurality of satellites, and the filter means further comprises:

means for rejecting continuous wave interference in a narrow band of frequencies including the maximum Doppler shift of the selected frequency due to relative motion between the satellites and the antenna means.

3. The system of claims 1 or 2 wherein the filter means further comprises:

means for converting the received signals to baseband; and

high pass filter means for rejecting a narrow band of frequencies at baseband.

4. The system of claim 3 wherein the filter means further comprises:

low pass filter means for rejecting frequencies outside a wide band of frequencies substantially including the signals whose spectrum was spread by a particular modulating code.

5. The system of claims 1 or 2 wherein the selected frequency is a suppressed center frequency carrier.

6. The system of claims 1 or 2 wherein the reconstructing means reconstructed a plurality of continuous wave components.

7. The system of claim 6 wherein the plurality of continuous wave components are related to the same selected frequency.

8. The system of claim 6 wherein the plurality of reconstructed components are related to the same spectrum spreading modulating code.

9. The system of claims 1 or 2 wherein the reconstructing means further comprises:

phase and frequency doubling means for reconstructing the signals whose spectrum was spread by a particular modulating code independently of externally derived knowledge of the information content of that modulating code.

10. The system of claim 9 wherein the rejecting and reconstructing means further comprise:

means for separating the received signals into first and second spectral components representing substantially different portions of the spectrum thereof; and

means for cross-correlating the spectral components to reconstruct the spread spectrum signals.

11. The system of claim 10 wherein the rejecting means further comprises:

means responsive to the first spectral component to reject continuous wave components therein related to the selected frequency; and

means responsive to the second spectral component to reject continuous wave components therein related to the selected frequency.

12. The system of claim 11 wherein each spectral component rejecting means further comprises:

high pass filter means for rejecting a narrow band of frequencies including the maximum Doppler shift of the selected frequency due to relative motion between the satellites and the antenna means; and

low pass filter means for rejecting signals outside a wide band of frequencies substantially including the signals spread by the particular modulating code.

13. The system of claim 10 wherein the first and second spectral commponents are upper and lower sidebands of a suppressed center frequency carrier implicit in the spread spectrum signals.

14. The system of claim 9, wherein the reconstructing means reconstructs continuous wave components implicit in the signals received from each of the satellites and the data deriving means further comprises:

means for deriving said position related data related to different satellites from the reconstructed signals based on the differences in frequencies thereof as received due to Doppler shift.

15. The system of claim 9, wherein the reconstructing means generates a second composite simultaneously including continuous wave components inmplicit in the signals received from each of the satellites and the data deriving means further comprises:

means for generating a series of predicted signals whose frequencies are related to the frequencies of the signals from each satellite as received;

means for correlating each of the series of predicted signals with the second composite signal to isolate the reconstructed components related to each satellite; and

means for deriving said position related data from each of the isolated components.

16. The method of deriving position related data from signals modulated by mutually orthogonal spectrum spreading codes, comprising the steps of:

receiving a composite of spread spectrum signals including potentially interfering continuous wave components with an antennas;

rejecting the continuous wave components related to a selected frequency from the composite of signals received, then;

reconstructing a continuous wave component related to the selected frequency from the remaining spread spectrum signals; and

deriving said position related data from the reconstructed component.

17. The method of claim 16 wherein the spread spectrum signals are transmitted concurrently with the same frequencies by each of a plurality of satellites and the interference rejecting step further comprises:

rejecting continuous wave interference in a narrow band of frequencies including the maximum Doppler shift of the selected frequency due to relative motion between the satellites and the antenna means.

18. The method of claims 16 or 17 wherein the interference rejecting step further comprises:

converting the received signals to baseband; and

rejecting a narrow band of frequencies at baseband.

19. The method of claim 18 wherein the interference rejecting step further comprises:

rejecting frequencies outside a wide band of frequencies substantially including the signals whose spectrum was spread by a particular modulating code.

20. The method of claim 16 or 17 wherein the selected frequency is a suppressed center frequency carrier.

21. The method of claim 20 wherein the reconstructing step reconstructs a plurality of continuous wave components.

22. The method of claim 21 wherein the plurality of continuous wave components are related to the same selected frequency.

23. The method of claim 21 wherein the plurality of reconstructed components are related to the same spectrum spreading modulating code.

24. The method of claims 16 or 17 wherein the reconstructing step further comprises:

doubling the phase and frequency of the signals whose spectrum was spread by a particular modulating code to reconstruct those signals independently of externally derived knowledge of the information content of that modulating code.

25. The method of claim 24 wherein the rejecting and reconstructing steps further comprise:

separating the received signals into first and second spectral components representing substantially different portions of the spectrum thereof; and

cross-correlating the spectral components to reconstruct the spread spectrum signals.

26. The method of claim 25 wherein the rejecting step further comprises:

rejecting continuous wave components in the first spectral component related to the selected frequency; and

rejecting continuous wave components in the second spectral component related to the selected frequency.

27. The method of claim 26 wherein each spectral component rejecting step further comprises:

means for rejecting a narrow band of frequencies including the maximum Doppler shift of the selected frequency due to relative motion between the satellites and the antenna means; and

rejecting signals outside a wide band of frequencies substantially including the signals spread by the particular modulating code.

28. The method of claim 25 wherein the first and second spectral components are upper and lower sidebands of a suppressed center frequency carrier implicit in the spread spectrum signals.

29. The method of claim 24 wherein the reconstructing step reconstructs continuous wave components implicit in the signals received from each of the satellites and the data deriving step further comprises:

deriving said portion related data related to different satellites from the reconstructed signals based on the difference in frequencies thereof as received due to Doppler shift.

30. The method of claim 24 wherein the reconstructing step generates a second composite simultaneously including continuous wave components implicit in the signals received from each of the satellites and the data deriving step further comprises:

generating a series of predicted signals whose frequencies are related to the frequencies of the signals from each satellite as received;

correlating each of the series of predicted signals with the second composite signal to isolate the reconstructed components related to each satellite; and

deriving said position related data from each of the isolated components.

31. A system for deriving phase data from signals modulated by mutually orthogonal spectrum spreading codes transmitted concurrently with the same frequencies by each of a plurality of satellites, comprising:

antenna means positioned at a first mark for receiving a first composite of overlapping spread spectrum signals from the satellites;

filter means for rejecting signals from the first composite signal received in a narrow band of frequencies related to the code modulated signals;

means for reconstructing the filtered first composite to form a second composite simultaneously including a plurality of reconstructed components related to the code modulated signals; and

applying predictions of the frequency histories of signals to derive phase data therefrom.

32. The system of claim 31 wherein the band of rejected frequencies substantially includes the Doppler shifted frequencies of the code modulated signals.

33. The system of claim 32 wherein the phase data derived are related to signals transmitted by a plurality of the satellites.

34. The system of claim 32, further comprising:

means for deriving at a second mark phase data related to signals concurrently transmitted by the plurality of satellites; and

means for processing the phase data from both marks to determine relative position information.

35. The system of claim 32 wherein the reconstructed components have discrete frequencies and phases related to the frequencies and phases of the code modulated signals.

36. The system of claim 32 wherein the reconstruction means further comprises:

means for doubling the phase and frequency of the filtered composite of spread spectrum signals to form the composite of reconstructed components.

37. The system of claim 32 wherein the filtering means further comprises:

means for separating the received signals into first and second components representing substantially different spectral portions thereof; and

the reconstructing means further comprises;

means responsive to the filter means for cross-correlating the spectral portions to generate the composite of reconstructed components.

38. The system of claim 37 wherein the spectral component separation means separates the spread spectrum signals into upper and lower sidebands of a center frequency carrier implicit therein.

39. The system of claim 37 wherein the correlating means further comprises:

means for generating a first binary signal representing the time varying sign of the first spectral component;

means for generating a second binary signal representing the time varying sigma of the second spectral component; and

means for correlating the first and second binary signals to form the composite of reconstructed components.

40. The system of claim 32 wherein the predicted frequency history means further comprises:

means for generating a signal whose frequency is related to an estimate of the Doppler shifted frequency of a code modulated signal as received; and

means for combining the estimate signal with the reconstructed components to separate the component related thereto.

41. The system of claim 40 wherein the predicted frequency history means further comprises:

means for varying the frequency of the estimate signal to track the frequency of the code modulated signals as received.

42. The system of claim 36 wherein the predicted frequency history means further comprises:

means for generating a predicted signal based on a prediction, made before the first composite is collected, of the Doppler shift of the signals from a selected satellite as received at the first mark; and

means for correlating the predicted signal with the reconstructed components to separate the reconstructed component whose frequency and phase are related to the frequency and phase of the code modulated signal.

43. The system of claim 42 wherein the phase data deriving means, further comprises:

means for varying the frequency of the predicted signal to maximize the separation of the related component.

44. The system of claim 32 wherein the phase data deriving means further comprises:

means for generating a series of signals whose frequencies are related to estimates of the frequencies of selected code modulated signals; and

means for combining each of the series of estimate signals with the composite of reconstructed components to separate the components related to each code modulated signal.

45. The system of claim 44 wherein the estimate generating generating means, further comprises:

means for varying the frequencies of the series of estimate signals to track the frequencies of the signals.

46. A method of deriving phase data from signals modulated by mutually orthogonal spectrum spreading codes, transmitted concurrently with the same frequencies by each of a plurality of satellites, comprising:

receiving a first composite of overlapping spread spectrum signals from the satellites with an antenna positioned at a first mark;

filtering the first composite to reject signals received in a narrow band of frequencies related to the code modulating signals;

reconstructing the filtered first composite to form a second composite simultaneously including a plurality of reconstructed components related to the code modulated signals; and

applying predictions of the frequency histories of signals to the second composite to derive said phase data therefrom.

47. The method of claim 46 wherein the band of rejected frequencies includes the Doppler shifted frequencies of the code modulated signals.

48. The method of claim 47 wherein the phase data derived are related to signals transmitted by a plurality of the satellites.

49. The method of claim 47, further comprising:

deriving at a second mark phase data related to signals concurrently transmitted by the plurality of satellites; and

processing the phase data from both marks to determine relative position information.

50. The method of claim 47 wherein the reconstructed components have discrete frequencies and phases related to the frequencies and phases of the code modulated signals.

51. The method of claim 47 wherein the reconstruction step further comprises:

doubling the phase and frequency of the filtered composite of spread spectrum signals to form the composite of reconstructed components.

52. The method of claim 47 wherein the filtering step further comprises:

separating the received signals into first and second components representing substantially different spectral portions thereof; and

the reconstructing step further comprises;

correlating the spectral portions after the filtering step to generate the composite of reconstructed components.

53. The method of claim 52 wherein the spectral component separation step separates the spread spectrum signals into upper and lower sidebands of a center frequency carrier implicit therein.

54. The method of claim 52 wherein the correlating step further comprises:

generating a first binary signal representing the time varying sign of the first spectral component;

generating a second binary signal representing the time varying sign of the second spectral component; and

correlating the first and second binary signals to form the composite of reconstructed components.

55. The method of claim 47 wherein the predicted frequency history step further comprises:

generating a signal whose frequency is proportional to an estimate of the Doppler shifted frequency of a code modulated signal as received; and

combining the estimate signal with the reconstructed components to separate the component related thereto.

56. The method of claim 55 wherein the predicted frequency history step further comprises:

varying the frequency of the estimate signal to track the frequency of the code modulated signals as received.

57. The method of claim 51 wherein the predicted frequency history step further comprises:

generating a predicted signal based on a prediction, made before the first composite is collected, of the Doppler shift of the signals from a selected satellite as received at the first mark; and

correlating the predicted signal with the reconstructed components to separate the reconstructed component whose frequency and phase are related to the frequency and phase of the code modulated signal.

58. The method of claim 57 wherein the phase data deriving step, further comprises:

varying the frequency of the predicted signal during the correlation step to maximize the separation of the related component.

59. The method of claim 47 wherein the phase data deriving step further comprises:

generating a series of signals whose frequencies are related to estimates of the frequencies of selected code modulated signals; and

combining each of the series of estimate signals with the composite of reconstructed components to separate the components related to each code modulated signal.

60. The method of claim 59 wherein the estimate generating generating step, further comprises:

varying the frequencies of the series of estimate signals to track the frequencies of the signals.

79. The method claimed in claims 77 or 48 wherein the sideband separating step further comprises:

splitting the received signals into two identical RF signals;

generating a pair of local oscillator output signals in phase quadrature at the nominal frequency of the suppressed carriers;

down-converting the identical RF signals to baseband in response to the in phase quadrature local oscillator signals;

phase shifting the down-converted RF signals; and

adding and subtracting the phase shifted results to separate the sidebands.

80. The method claimed in claim 79 wherein the sideband cross-correlation step further comprises:

clipping the sideband signals to form first and second binary signals representing the time varying signs of the sidebands.

61. A GPS receiver for determining position related phase data comprising:

antenna means for collecting a first composite of overlapping L band signals modulated by mutually orthogonal, spectrum spreading codes concurrently transmitted at the same nominal frequencies by a plurality of NAVSTAR satellites;

filter means for rejecting signals from the first composite in a narrow band including the Doppler shifted frequencies of a signal suppressed by code modulation from the signals transmitted by each of the satellites;

means responsive to the filter means for reconstructing the suppressed signals; and

means for determining said position related phase data from the reconstructed signals.

62. The receiver of claim 61 wherein the filter means further comprises:

means for rejecting signals outside of a wide band of signals including substantially the entire spectrum of signals spread by that code modulation.

63. The receiver of claims 61 or 62 wherein the suppressed signal reconstructed means comprises:

means for reconstructing an orthogonal component of the suppressed signal independently of externally derived knowledge of the information content of the modulating code applied to that component.

64. The receiver of claim 63 wherein the reconstruction means comprises:

means for separating the first composite of spread spectrum signals into upper and lower sidebands of a center frequency carrier implicit in the signals from the satellites; and

means for cross-correlating the sidebands.

65. The method of determining position related data comprising:

collecting a first composite of overlapping L band signals modulated by mutually orthogonal, spectrum spreading codes concurrently transmitted at the same nominal frequencies by a plurality of NAVSTAR satellites;

rejecting signals from the first composite in a narrow band including the Doppler shifted frequencies of a signal suppressed by code modulation from the signals transmitted by each of the satellites;

then

reconstructing the suppressed signal from each satellites; and

then

determining said position related data therefrom.

66. The method of claim 65 further comprising:

rejecting signals outside of a wide band of signals including substantially the entire spectrum of signals spread by the code modulation.

67. The method of claims 65 or 66 wherein the suppressed signal is reconstructed independently of externally derived knowledge of the information content of the modulating code.

68. The method of claim 67 further comprising:

separating the first composite of spread spectrum signals into upper and lower sidebands of a center frequency carrier implicit in the signals from the satellites; and

cross-correlating the sidebands.

69. A system for determining position information from the phases of suppressed signals including mutually orthogonal code modulated components implicit in spread spectrum signals transmitted concurrently at the same frequencies by each of a plurality of satellites independently of externally derived knowledge of the information content of the code modulation, comprising:

antenna means for receiving a first composite of overlapping spread spectrum signals at a mark;

means for rejecting a narrow band of the spread spectrum signals at a selected frequency;

means for reconstructing the spread spectrum signals to provide a second composite simultaneously including reconstructed signals from each of the satellites nominally at the selected frequency; and

means for determining position information deriving the phase of the reconstructed signals from each satellite by correlating the second composite with a series of predicted signals whose frequencies are related to the Doppler shifts encountered by the signals from the satellites.

70. A method of determining position information from the phases of suppressed signals including mutually orthogonal code modulated components implicit in spread spectrum signals transmitted concurrently at the same frequencies by each of a plurality of satellites independently of externally derived knowledge of the information content of the code modulation, comprising:

receiving a first composite of overlapping spread spectrum signals at a first mark with an antenna;

rejecting a narrow band of the spread spectrum signals at a selected frequency;

reconstructing the spread spectrum signals to provide a second composite simultaneously including reconstructed signals from each of the satellites nominally at the selected frequency; and

determining position information by deriving the phase of the reconstructed signals from each satellite by correlating the second composite with a series of predicted signals whose frequencies are related to the Doppler shifts encountered by the signals from the satellites.

71. A GPS receiver for determining the position of a first mark, comprising:

antenna means for collecting at the first mark a first composite of overlapping L band signals modulated by satellite specific mutually orthogonal, spectrum spreading C/A codes concurrently transmitted at the same nominal frequencies by each of a plurality of NAVSTAR satellites;

local oscillator means for converting the received signals to baseband;

sideband separator means responsive to the baseband signals for separating said signals into components representing the upper and lower sidebands of the suppressed L band center frequency carriers;

interference rejecting filter means responsive to each of the sideband components for rejecting signals therefrom in a narrow band including the Doppler shifted frequencies of the L band center frequency carriers suppressed by code modulation from the signals transmitted by each of the satellites;

one bit clipper means means responsive to the filtered sideband components for generating first and second binary signals representing the time varying signs of the sideband components;

sideband correlation means for cross-correlating the first and second binary signals to generate a second composite of reconstructed L band center frequency carriers;

numerical oscillator assemblies for generating signals whose frequencies represent predictions of the Doppler shifted frequency of the signals received from each particular satellite;

local model correlation means for cross-correlating the signals from the numerical oscillator asssemblies and the second composite of reconstructed L band center frequency carriers to select therefrom the reconstructed carriers related to particular satellites;

phase detecting means responsive to the selected reconstructed carriers for determining the phases thereof; and

means for determining the position of the first mark from the phases of the selected reconstructed center frequency carriers.

72. The receiver of claim 71 wherein the interference rejecting filter means further comprises:

means for rejecting signals outside of a wide band of signals including substantially the entire spectrum of satellite signals spread by that code modulation.

73. A GPS receiver for determining a baseline vector between two marks, comprising:

an antenna at a first mark for receiving overlapping, carrier suppressed L band signals concurrently transmitted at the same nominal frequencies by each of a plurality of NAVSTAR satellites;

a sideband separator for separating the received signals into upper and lower sidebands of the suppressed L band carriers;

a pair of filters for rejecting signals from the upper and lower sidebands originating in a narrow band surrounding the Doppler shifted frequencies of the suppressed carriers;

a correlator for cross-correlating the filtered, separated sidebands to form a composite of reconstructed suppressed carriers;

a plurality of satellite tracking channels responsive to the composite of suppressed carriers for determining the phases of reconstructed suppressed carriers related to selected satellites;

means for determining the phases of reconstructed carriers from signals concurrently received from the selected satellites at a second mark; and

means for computing the baseline vector between the marks from the reconstructed carrier phases so determined.

74. The GPS receiver claimed in claim 73 wherein the satellite tracking channels further comprises:

a numerical oscillator for generating signals whose time varying frequencies represent predictions of the Doppler shifted frequencies of the signals received from a selected satellite;

a correlator for cross-correlating the signals from the numerical oscllator and the composite of reconstructed carriers to select therefrom the reconstructed carrier related to the selected satellite; and

a phase detector for determining the time varying phase of the selected reconstructed carrier.

75. The GPS receiver claimed in claims 73 or 74 wherein the sideband separator further comprises:

an RF power splitter for splitting the received signals into two identical RF signals;

a quadrature hybrid for generating a pair of local oscillator output signals in phase quadrature at the nominal frequency of the suppressed carriers;

a pair of doubly balanced mixers for down-converting the identical RF signals to baseband in response to the in phase quadrature local oscillator signals; and

a second quadrature hybrid for phase shifting the down-converted RF signals and adding and subtracting the phase shifted results to separate the sidebands.

76. The GPS receiver claimed in claim 75 wherein each of the pair of filters further comprises:

a high pass filter for rejecting low frequency down-converted signals representing received signals originating at frequencies near the suppressed carriers; and

a low pass filter for rejecting signals passed by the high pass filter originating outside of the bandwidth of the carrier suppressed signals transmitted by the satellites.

77. A method of determining a baseline vector between two marks from overlapping, carrier suppressed L band signals concurrently transmitted at the same nominal frequencies by each of a plurality of NAVSTAR satellites and received at the marks, comprising the steps of:

separating the signals received at each mark into upper and lower sidebands of the suppressed L band carriers;

cross-correlating the separated sidebands to form a composite of reconstructed suppressed carriers related to each mark;

determining the phases of reconstructed suppressed carriers at each mark related to a plurality of selected satellites; and

computing the baseline vector between the marks from the reconstructed carrier phases so determined.

78. The method claimed in claim 77 wherein the phase determining step further comprises:

generating signals whose time varying frequencies represent predictions of the Doppler shifted frequencies of the signals received from selected satellites;

cross-correlating the predicted signals with the composite of reconstructed carriers to select therefrom the reconstructed carriers related to selected satellites; and

determining the time varying phases of the reconstructed carriers so selected.