High frequency spread spectrum positioning system and method therefor

• US 4,665,404 A
• Filed: 10/19/1984
• Issued: 05/12/1987
• Est. Priority Date: 10/24/1983
• Status: Expired due to Fees

• Current Assignee: Offshore Navigation Incorporated
• Original Assignee: Offshore Navigation Incorporated
• Inventors: Van Doren, Lawrence, Christy, Edmund H., Rouquette, Robert E.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Gregory, Bernarr Earl
• Application Number:
  US06/662,889
• Time in Patent Office: 935 Days
• Field of Search: 343/6.5 R, 343/6.8 R, 343/7.5, 343/356, 343/357, 343/394, 343/421, 343/463, 343/387, 364/423, 364/449, 364/452, 364/458, 375/1.5, 375/1, 342/142-151, 356/357, 356/394, 421/463
• US Class Current: 342/463
• CPC Class Codes: G01S 11/08 using synchronised clocks
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location

Abstract

The system includes a method and apparatus for transmitting a spread spectrum signal from each of a plurality of base stations. The spread spectrum signal has a predetermined timing and has a ground wave component and a sky wave component. The signal is transmitted with a repetition time at least as great as a maximum anticipated delay time of the sky wave component such that the ground wave component of the transmitted spread spectrum signal can be distinguished from the sky wave component. The signal is detected at each of a plurality of mobile stations and the timing of the detected signal is compared to a local timing signal. The phase difference between these signals is indicative of the range of the base station from the mobile station.

Claims

1. A system for enabling a mobile station to make position determinations relative to at least two base stations, comprising:

at lest two stationary base stations, each said base station comprising;

a base station clock having a predetermined timing;

means synchronized with said base station clock for transmitting a spread spectrum signal having a timing indicative having a ground wave component and a sky wave component, said spread spectrum signal having a repetition time at least as great as a maximum anticipated delay time of said spread spectrum signal sky wave component whereby said ground wave component of said transmitted spread spectrum signal can be distinguished from said sky wave component of said spread spectrum signal;

at least one mobile station comprising;

a mobile station clock synchronized with said base station clock;

detection means for receiving said spread spectrum signal, despreading said received signal and outputting a detected despread signal;

means for receiving said detected despread signal and comparing said timing to the timing of said mobile station clock for producing a phase difference signal indicative of range from said base station;

wherein each said base station spread spectrum signal is at a different frequency, whereby a plurality of ranges can be determined simultaneously from said individual base stations and used to determine location of said mobile station by calculating a range to each of said base stations.

2. A system as set forth in claim 1, wherein said means for transmitting comprises means for generating a pseudorandom noise code, means for generating a carrier signal, and means for modulating said carrier signal with said pseudorandom noise code.

3. A system as set forth in claim 2, wherein said carrier signal is at a frequency in the range 1 MHz to 4 MHz.

4. A system as set forth in claim 2, wherein said detection means comprises means for duplicating said pseudorandom noise code, and means for cross correlating said receiver spread spectrum signal with said duplicated pseudorandom noise code.

5. A system as set forth in claim 2, wherein said pseudorandom noise code has a chip time less than the minimum expected delay time of said sky wave component.

6. A system as set forth in claim 2, wherein said detection means include a notch filter for filtering out narrow band interference in said received signal, and means for analyzing said received signal and matching the stopband of said notch filter to said narrow band interference.

7. A system as set forth in claim 2, wherein said pseudorandom noise code has an unambiguous length not less than one fourth of the maximum expected range to be measured.

8. A system as set forth in claim 2, wherein said pseudorandom noise code has an unambiguous length not less than the maximum expected range to be measured.

9. A system as set forth in claim 2, wherein said pseudorandom noise code has an unambiguous length of approximately 400 miles.

10. A system as set forth in claim 2 including means for adding digital communication data to said pseudorandom noise code and said detection means includes means for identifying said digital communication data.

11. A system as set forth in claim 10, wherein said adding means produces a phase shift of said transmitted signal to distinguish each bit of said digital communication data, and said means for identifying said digital communication data comprises a phase detector.

12. A system as set forth in claim 10, wherein said mobile station includes a mobile station transmitter, each said base station includes a base station receiver tuned to receive signals transmitted by the mobile station transmitter.

13. A system as set forth in claim 12, wherein said mobile station transmitter is operative to transmit a signal to said base station receiver indicative of the timing of said mobile station clock, said base station including means for comparing the phase of said mobile station timing with the phase of said base station clock and generating a signal indicative of the phase difference therebetween, said adding means being connected to receive said phase difference signal and to transmit said phase difference signal to said mobile station whereby said mobile station is able to maintain accurate synchronization between said mobile station clock and said based station clock and obtain a round trip determination of range.

14. A system as set forth in claim 12, wherein each mobile station transmitter transmits a pseudorandom noise code at a different frequency than the pseudorandom noise codes transmitted by said base stations.

15. A system as set forth in claim 10, wherein said base station includes a base station receiver for receiving signals from said mobile station, said transmitting means including means for transmitting said spread spectrum signal only during transmit periods of a predetermined length, said transmit periods being followed by receive periods during which said base station is capable of receiving on said base station receiver.

16. A system as set forth in claim 15, wherein each said transmit period has an duration equal to a plurality of repetition times of said spread spectrum signal.

17. A system as set forth in claim 16, wherein each said transmit period is equal to approximately 8 of said repetition times.

18. A system as set forth in claim 15, wherein said mobile station includes a transmitter for transmitting to said base station receiver and wherein said mobile station includes means establishing transmit periods for permitting signal transmissions and establishing receive periods for permitting signal reception, said mobile station transmit and receive periods being 180 degrees out of phase with said base station transmit and receive periods.

19. A system as set forth in claim 18 including means for synchronizing said base station transmit and receive periods with said mobile station transmit and receive periods, said synchronization means comprising means for correlating said pseudorandom code transmitted by said base station with a locally generated duplicate of said pseudorandom code having portion in phase with said transmitted pseudorandom code and having a portion out of phase with said transmitted pseudorandomm code to produce a predetermined correlation function when synchronization occurs.

20. A system as set forth in claim 19 further including means for varying the rate of said locally generated duplicate of said pseudorandom code in response to the output of said correlating means.

21. A system as set forth in claim 2, wherein the pseudorandom noise codes for esach of said base statiins have similar chip times.

22. A system as set forth in claim 21, wherein the carrier frequencies for said base stations are different from each other and are chosen such that each transmitted spread spectrum signal has spectral lines which are different from the spectral lines of the other spread spectrum signals.

23. A system as set forth in claim 1, wherein said carrier signal frequency is less than 60 MHz.

40. A method as set forth in claim 19 including synchronizing the base station transmit and receive periods with the mobile station transmit and receive periods by correlating the pseudorandom code transmitted by the base station with a locally generated duplicate of the pseudorandom code which has a portion in phase with the transmitted pseudorandom code and a portion out of phase with the transmitted pseudorandom code to produce a predetermined correlation function indicative of synchronization.

41. A method as set forth in claim 40 further including varying the rate of said locally generated duplicate in response to said correlation function.

24. A method for enabling a mobile station to make position determinations relative to at least two stationary base stations, comprising:

at each base station, transmitting a spread spectrum signal having a predetermined timing, having a ground wave component and a sky wave component, and having a repetition time at least as great as a maximum anticipated delay time of said sky wave component; and

at said mobile station, detecting said spread spectrum signal, despreading said spread spectrum signal, and comparing the timing of said despread signal to a locally generated timing signal for producing a phase difference signal indicative of the range of said base station;

wherein each base station spread spectrum signal is transmitted at a different frequency and said mobile station determines a separate range from each base station to determine a location of said mobile station.

25. A method as set forth in claim 24, wherein the step of transmitting comprises generating a pseudorandom noise code, generating a carrier signal, and modulating the carrier signal with the pseudorandom noise code.

26. A method as set forth in claim 25 including the step of generating said pseudorandom noise code with a chip time less than the minimum expected delay time of said sky wave component.

27. A method as set forth in claim 25 including the step of generating said carrier signal at a frequency in the range of 1 MHz to 4 MHz.

28. A system as set forth in claim 25, wherein the step of detecting comprises duplicating the pseudorandom noise code and cross correlating the spread spectrum signal with the duplicated pseudorandom noise code.

29. A method as set forth in claim 25 including, at each mobile station, analysing received signals and filtering out any narrow band interference in the received signals prior to detection.

30. A method as set forth in claim 25, wherein said pseudorandom noise code is generated with a length not less than one fourth of the maximum expected range to be measured.

31. A method as set forth in claim 25, wherein the pseudorandom noise code is generated with an unambiguous length not less than the maximum expected range to be measured.

32. A method as set forth in claim 25 including the step of adding digital communication data to the pseudorandom noise code prior to transmission and wherein the step of detecting includes identifying the digital communication data.

33. A method as set forth in claim 32, wherein the step of adding comprises producing a phase shift of the pseudorandom noise code to distinguish each bit of the digital communication data, and wherein the step of detecting the digital communication data comprises detecting a phase shift.

34. A method as set forth in claim 32 including, for said mobile station, transmitting a signal to each base station receiver indicative of the timing of said mobile station, and including, at each base station, the step of comparing the phase of the mobile station timing signals with the phase of the signal transmitted by that base station, generating a signal indicative of the phase difference therebetween, and adding the phase difference signal to the transmitted signal.

35. A method as set forth in claim 34 including, at said mobile station, adjusting the ranging information derived by said mobile station in response to a received phase difference signal from a base station.

36. A system as set forth in claim 32, wherein said mobile station transmits a pseudorandom noise code at a frequency different from the pseudorandom noise code transmitted by the base stations.

37. A method as set forth in claim 32, wherein each base station receives signals from said mobile station and transmits spread spectrum signals only during transmit periods of a predetermined length and receives signals only during receive periods of a predetermined length.

38. A method as set forth in claim 37, wherein the transmit periods have a duration equal to a plurality of repetition times oof the spread spectrum signal.

39. A method as set forth in claim 37, wherein the mobile station transmits signals to the base stations and wherein transmit periods for the mobile station are established followed by receive periods for the mobile station, and wherein the mobile station receive periods and transmit periods are 180 degrees out of phase with the base station receive periods and transmit periods.