Synchronizing ranging signals in an asynchronous ranging or position system

• US 7,339,526 B2
• Filed: 07/30/2004
• Issued: 03/04/2008
• Est. Priority Date: 07/30/2004
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Novariant Incorporated (Kubota Corporation)
• Inventors: Zimmerman, Kurt R.
• Primary Examiner(s): Tarcza; Thomas H.
• Assistant Examiner(s): Mull; Fred H
• Application Number:
  US10/909,234
• Publication Number:
  US 20060022873A1
• Time in Patent Office: 1,313 Days
• Field of Search: 342/357.02, 342/357.06, 342/357.14, 342/450, 342/457, 342463-464, 342/458
• US Class Current: 342/464
• CPC Class Codes: G01S 19/04 providing carrier phase data
• CPC Class Codes: G01S 19/071 DGPS corrections
• CPC Class Codes: G01S 19/11 wherein the cooperating elements are pseudolites or satellite radio beacon positioning system signal repeaters
• CPC Class Codes: G01S 19/32 Multimode operation in a single same satellite system, e.g. GPS L1/L2
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: G01S 19/41 Differential correction, e.g. DGPS [differential GPS]
• CPC Class Codes: G01S 19/44 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method
• CPC Class Codes: G01S 5/009 Transmission of differential positioning data to mobile

Abstract

In a local positioning system, the land-based transmitters include free running oscillators or oscillators free of clock synchronization with any remote oscillator. A reference receiver receives the ranging signals from different transmitters and generates timing offset information, such as code phase measurements. The timing offset information is then communicated back to transmitters. The temporal offset information indicates relative timing or phasing of the different transmitted ranging signals to the reference receiver. The transmitters then transmit the temporal offset information with the ranging signals, such as modulating the transmitted code by the timing offset information. A mobile receiver is operable to receive the ranging signals and timing offset information in a same communications path, such as on a same carrier. Position is determined with the temporal offset information and the ranging signals. The temporal offset information for the various transmitters allows the mobile receiver to more accurately determine position than in an unsynchronized system.

Claims

1. A system for transmitting to determine a range or position from a transmitter relative to a first receiver, the system comprising:

a first transmitter operable to transmit a ranging signal with a modulation rate of a code being at least about 30 MHz, the transmission being to the first receiver in a line of sight with the first transmitter; and

a first oscillator connected with the first transmitter, the first oscillator being free-running, the ranging signal responsive to the first oscillator.

2. The system of claim 1 wherein the modulation rate is at least about 60 MHz.

3. The system of claim 1 wherein the modulation rate is less than about 250 MHz.

4. The system of claim 1 wherein the ranging signal has an X-band carrier wave responsive to the first oscillator.

5. The system of claim 1 wherein the ranging signal has an ISM band carrier wave responsive to the first oscillator.

6. The system of claim 1 wherein the first receiver is within a region of operation and wherein the code has a chip width in space at most a longest dimension of the region of operation.

7. The system of claim 1 wherein the first transmitter comprises a first land based transmitter.

8. The system of claim 1 wherein the first receiver is within a region of operation and wherein the code has a code length in space approximately equal to a longest dimension of the region of operation.

9. The system of claim 8 wherein the code length in space is less than about 15 kilometers.

10. The system of claim 1 wherein the ranging signal is a code division multiple access signal transmitted in a time division multiple access time slot with a blank period about as long as a code length.

11. The system of claim 1 wherein the first transmitter comprises a first land based transmitter;

further comprising;

a second receiver spaced from the first receiver, both the first and second receivers operable to receive the ranging signal; and

a processor operable to determine a position as a function of a differential measurement of the ranging signal between the first and second receivers, the differential measurement having a code based accuracy of better than ten centimeters.

12. The system of claim 11 wherein the first receiver comprises a mobile receiver and the second receiver comprises a stationary receiver.

13. The system of claim 1 further comprising:

a processor operable to determine the range or position as a function of the code, the code having an accuracy to better than one meter.

14. The system of claim 1 wherein the first oscillator comprises a first crystal oscillator.

15. The system of claim 14 further comprising a first dielectric resonator oscillator phase locked to the first crystal oscillator, the modulation rate being a multiple of a frequency of the first crystal oscillator and a carrier frequency being responsive to a frequency of the first dielectric resonator oscillator.

16. The system of claim 1 wherein the first oscillator comprises a first dielectric resonator oscillator.

17. The system of claim 1 further comprising:

a second transmitter spaced from the first transmitter; and

a second oscillator connected with the second transmitter;

wherein the first oscillator is free of synchronization with the second oscillator.

18. The system of claim 17 wherein the first transmitter is operable to transmit the ranging signal in a first time slot and the second transmitter is operable to transmit in a second time slot different than the first time slot, the first time slot synchronized with the second time slot to within at least three microseconds.

19. The system of claim 1 wherein the first oscillator is free-running relative to any external source.

20. The system of claim 1 wherein the modulation rate is at least 30 MHz.

21. A method for transmitting to determine a range or position from a transmitter relative to a first receiver, the method comprising:

(a) generating a ranging signal in response to a first oscillator, a phase of the oscillator being unsynchronized with any remote oscillator; and

(b) transmitting the ranging signal with a modulation rate of a code being at least about 30 MHz;

(c) generating an additional ranging signal in response to a second oscillator from a source remote from the first oscillator, wherein the first oscillator is free of synchronization with the second oscillator; and

(d) transmitting the additional ranging signal with a modulation rate of a code being at least about 30 MHz.

22. The method of claim 21 wherein (b) comprises transmitting with the modulation rate is at least about 60 MHz and less than about 250 MHz.

23. The method of claim 21 wherein (a) comprises generating the ranging signal with an X-band or an ISM band carrier wave responsive to the first oscillator.

24. The method of claim 21 wherein (b) comprises transmitting from a first land based transmitter;

and

further comprising;

receiving the ranging signal within a region of operation, wherein the code has a chip width in space at most approximately equal to a longest dimension of the region of operation.

25. The method of claim 21 wherein (b) comprises transmitting from a first land based transmitter;

and

further comprising;

receiving the ranging signal within a region of operation, wherein the code has a code length in space approximately equal to a longest dimension of the region of operation and less than about 15 kilometers.

26. The method of claim 21 wherein (b) comprises transmitting the ranging signal as a code division multiple access signal in a time division multiple access time slot with a blank period about as long as a code length.

27. The method of claim 21 wherein (b) comprises transmitting from a first land based transmitter;

and

further comprising;

receiving the ranging signal at both the first and a second receiver spaced from the first receiver;

communicating information responsive to the ranging signal between the first and second receivers; and

determining a position as a function of a differential measurement of the ranging signal between the first and second receivers, the differential measurement having a code based accuracy of better than ten centimeters.

28. The method of claim 21 wherein (a) comprises:

(a1) generating the code at a multiple of a first frequency of a crystal oscillator;

(a2) phase locking a dielectric resonator oscillator to the crystal oscillator;

(a3) generating a carrier wave as a function of a second frequency of the dielectric resonator oscillator; and

(a4) mixing the code with the carrier wave.

29. The method of claim 21 further wherein:

the additional ranging signal transmitted in a second time slot different than a time slot for transmitting the ranging signal of (b), the first time slot synchronized with the second time slot to within at least three microseconds.

30. The method of claim 21 wherein transmitting comprises transmitting with the modulation rate being at least 30 MHz.

31. A system for determining a position of a first receiver, the system comprising:

a first land-based transmitter having a first oscillator, the first land-based transmitter operable to transmit a first ranging signal with a first modulation rate of a first code being at least about 30 MHz, and the first ranging signal responsive to the first oscillator;

a second land-based transmitter having a second oscillator, the second land-based transmitter operable to transmit a second ranging signal with a second modulation rate of a second code being at least about 30 MHz, and the second ranging signal responsive to the second oscillator;

a third land-based transmitter having a third oscillator, the third land-based transmitter operable to transmit a third ranging signal with a third modulation rate of a third code being at least about 30 MHz, and the third ranging signal responsive to the third oscillator;

a fourth land-based transmitter having a fourth oscillator, the fourth land-based transmitter operable to transmit a fourth ranging signal with a fourth modulation rate of a fourth code being at least about 30 MHz, and the fourth ranging signal responsive to the fourth oscillator;

a second receiver spaced from the first receiver, both the first and second receivers operable to receive the first, second and third ranging signals;

wherein the first, second and third oscillators are free of phase synchronization with each other;

wherein the first receiver is mobile; and

a processor operable to determine the position as a function of a differential measurement of the first, second, third, and fourth ranging signals between the first and second receivers, the differential measurement having a code based accuracy of better than ten centimeters.

32. The system of claim 31 wherein the first, second, third and fourth modulation rates are each at least about 30 MHz and less than about 250 MHz;

and

wherein the first, second and third ranging signals each have an X-band carrier wave responsive to the first, second and third oscillators, respectively.

33. The system of claim 31 wherein the first, second, third and fourth transmitters and first and second receivers are within a region of operation wherein the first, second, third and fourth code each has a chip width in space at most approximately equal to a longest dimension of the region of operation.

34. The system of claim 31 wherein the first, second, third and fourth transmitters and first and second receivers are within a region of operation with a longest dimension of less than about 15 kilometers and wherein the first, second, third and fourth codes each has a code length in space approximately less than twice the longest dimension of the region of operation.

35. The system of claim 31 wherein the first, second, third and fourth ranging signals are each code division multiple access signals transmitted in first, second, third and fourth time division multiple access time slots, respectively, each time slot having a blank period of an order of magnitude of a length of the first, second, third and fourth codes, respectively, the first, second, third and fourth time division multiple access time slots synchronized to within at least three microseconds.

36. The system of claim 31 wherein the first, second, third and fourth oscillators are free-running relative to any external source.

37. The system of claim 31 wherein the first, second, third and fourth modulation rates are substantially equal.

38. The system of claim 31 wherein the first, second, third and fourth codes are substantially the same.

39. The system of claim 31 wherein the first, second, third, and fourth modulation rates are each at least 30 MHz.