Method and apparatus for determining the position of a mobile communication device

• US 6,801,782 B2
• Filed: 02/06/2001
• Issued: 10/05/2004
• Est. Priority Date: 08/02/1999
• Status: Expired due to Fees

• Current Assignee: Stingray IP Solutions LLC (Acacia Research Corporation)
• Original Assignee: ITT Manufacturing Enterprises, Inc. (ITT, Inc.)
• Inventors: McCrady, Dennis D., Cummiskey, Peter, Doyle, Lawrence J., Forstrom, Howard
• Primary Examiner(s): Maung, Nay
• Assistant Examiner(s): SOBUTKA, PHILIP
• Application Number:
  US09/777,625
• Publication Number:
  US 20010053699A1
• Time in Patent Office: 1,337 Days
• Field of Search: 455/456--45, 455/457, 455/517, 455/466, 455/67.1, 455/65, 342/457.1, 375/138, 375/347
• US Class Current: 455/517
• CPC Class Codes: G01S 13/46 Indirect determination of position data
• CPC Class Codes: G01S 2013/466 by Trilateration, i.e. two antennas or two sensors determine separately the distance to a target, whereby with the knowledge of the baseline length, i.e. the distance between the antennas or sensors, the position data of the target is determined
• CPC Class Codes: G01S 5/0205 Details
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/0218 Multipath in signal reception
• CPC Class Codes: G01S 5/0244 Accuracy or reliability of position solution or of measurements contributing thereto
• CPC Class Codes: G01S 5/0294 Trajectory determination or predictive filtering, e.g. target tracking or Kalman filtering
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A position location communication system determines the position of a mobile master radio using a round-trip messaging scheme in which the time of arrive (TOA) of ranging signals is accurately determined to yield the range estimates required to calculate the position of the mobile radio. The master radio transmits ranging signals to plural reference radios which respond by transmitting reply ranging signals. Upon reception of the reply ranging signal, the master radio determines the range to the reference radio from the signal propagation time. Any combination of fixed or mobile radios having known positions can be used as the reference radios for another mobile radio in the system. Individual radios do not need to be synchronized to a common time reference, thereby eliminating the need for highly accurate system clocks. Errors in TOA estimates are minimized by performing internal delay calibration, Doppler compensation, leading-edge-of-the-signal curve fitting and frequency diversity techniques.

Claims

1. A mobile communication device capable of determining range to a reference communication device by exchanging ranging signals with the reference communication device, comprising:

a transmitter configured to transmit to the reference communication device a sequence of outbound ranging signals at different carrier frequencies;

a receiver configured to receive from the reference communication device a sequence of reply ranging signals at the different carrier frequencies in response to the outbound ranging signals; and

a processor configured to select from among the reply ranging signals a reply ranging signal at a carrier frequency providing a highest signal timing accuracy, said processor determining a time of arrival of the selected reply ranging signal and the range to the reference communication device from a round-trip signal propagation time of the selected reply ranging signal and a corresponding outbound ranging signal, and wherein said processor performs Doppler compensation on the selected reply ranging signal to reduce errors in estimating the time of arrival of the selected reply ranging signal.

2. The mobile communication device of claim 1, wherein said processor selects the reply ranging signal whose carrier frequency minimizes multipath interference.

3. The mobile communication device of claim 1, wherein said processor comprises:

means for rotating a phase of each reply ranging signal to incremental phase angles over a range of phase angles, said processor selecting from among the reply ranging signals at each carrier frequency and incremental phase angle a reply ranging signal at a carrier frequency and phase providing a highest signal timing accuracy.

4. The mobile communication device of claim 1, wherein

said reference communication device transmits each reply ranging signal at a predetermined turn-around time after reception of an outbound ranging signal;

and

said mobile communication device transmits each successive outbound ranging signal at the predetermined turn-around time after reception of a reply ranging signal, said processor computing the range to the reference communication device using the predetermined turn-around time.

5. The mobile communication device of claim 1, wherein said processor estimates the time of arrival of the selected reply ranging signal using signal curve fitting and computes the range to the reference communication device using a timing adjustment determined from the signal curve fitting.

6. The mobile communication device of claim 5, wherein:

the reference communication device estimates the time of arrival of the outbound ranging signals using signal curve fitting; and

said processor of the mobile communication device computes the range to the reference communication device using a timing adjustment determined from the signal curve fitting performed by the reference communication device on the outbound ranging signal corresponding to the selected reply ranging signal.

7. The mobile communication device of claim 1, wherein said mobile communication device performs internal delay calibration to reduce errors in estimating a time of arrival of the reply ranging signal and computes the range to the reference communication device using a timing delay determined from the internal delay calibration.

8. The mobile communication device of claim 7, wherein:

the reference communication device performs internal delay calibration to reduce errors in estimating a time of arrival of the outbound ranging signals; and

said processor of the mobile communication device computes the range to the reference communication device using a timing delay determined from the internal delay calibration performed by the reference communication device.

9. The mobile communication device of claim 1, wherein said mobile communication device determines ranges to a plurality of reference communication devices by exchanging ranging signals with each of the reference communication devices, said processor determining the position of said mobile communication device from known positions of said reference communication devices and the range to each of said reference communication devices.

10. The mobile communication device of claim 1, further comprising:

a low accuracy clock adapted to maintain a local timing reference, said mobile communication device determining a time of transmission of the outbound ranging signals and a time of arrival of the reply ranging signals in accordance with the local timing reference, said low accuracy clock not being synchronized with a clock maintaining a local timing reference for the reference communication device.

11. The mobile communication device of claim 1, wherein said mobile communication device is a handheld radio.

12. The mobile communication device of claim 1, wherein said mobile communication device is configured to be carried on a human body.

13. The mobile communication device of claim 1, wherein said mobile communication device is incorporated into clothing worn on the body.

14. The mobile communication device of claim 1, wherein said mobile communication device is a mobile telephone.

15. The mobile communication device of claim 1, wherein said mobile communication device operates onboard a moving vehicle.

16. The mobile communication device of claim 1, wherein said mobile communication device is capable of exchanging ranging signals with reference communication devices while indoors.

17. The mobile communication device of claim 1, wherein said mobile communication device is coupled to a valuable item to facilitate tracking of the valuable item.

18. A position location system for determining the position of a mobile communication device, comprising:

a plurality of reference communication devices having known positions, each configured to transmit and receive ranging signals; and

a mobile communication device configured to exchange ranging signals with said reference communication devices, said mobile communication device transmitting to each reference communication device a sequence of outbound ranging signals at different carrier frequencies, each of said reference communication devices transmitting a sequence of reply ranging signals at the different carrier frequencies in response to the outbound ranging signals, wherein;

said mobile communication device determines the range to each reference communication device from a round-trip signal propagation time of a selected outbound ranging signal and a corresponding reply ranging signal transmitted at a carrier frequency providing a highest signal timing accuracy, performs Doppler compensation on the selected reply ranging signal to reduce errors in estimating the time of arrival of the selected reply ranging signal, and determines the position of said mobile communication device from the known positions of said reference communication devices and the range to each reference communication device.

19. The system of claim 18, wherein said mobile communication device selects the reply ranging signal whose carrier frequency minimizes multipath interference.

20. The system of claim 18, wherein said mobile communication device comprises:

means for rotating a phase of each reply ranging signal to incremental phase angles over a range of phase angles, said mobile communication device selecting from among the reply ranging signals at each carrier frequency and incremental phase angle a reply ranging signal at a carrier frequency and phase providing a highest signal timing accuracy for each reference communication device.

21. The system of claim 18, wherein:

each reference communication device transmits each reply ranging signal at a predetermined turn-around time after reception of an outbound ranging signal; and

said mobile communication device transmits each successive outbound ranging signal to each communication device at the predetermined turn-around time after reception of a reply ranging signal, said processor computing the range to each reference communication device using the predetermined turn-around time.

22. The system of claim 18, wherein said mobile communication device estimates the time of arrival of each selected reply ranging signal using signal curve fitting and computes the range to each reference communication device using a timing adjustment determined from the signal curve fitting.

23. The system of claim 22, wherein:

each reference communication device estimates the time of arrival of the outbound ranging signals using signal curve fitting; and

said mobile communication device computes the range to each reference communication device using a timing adjustment determined from the signal curve fitting performed by each reference communication device on the outbound ranging signal corresponding to the selected reply ranging signal.

24. The system of claim 18, wherein said mobile communication device performs internal delay calibration to reduce errors in estimating a time of arrival of the reply ranging signal and computes the range to each reference communication device using a timing delay determined from the internal delay calibration.

25. The system of claim 24, wherein:

each reference communication device performs internal delay calibration to reduce errors in estimating a time of arrival of the outbound ranging signals; and

said mobile communication device computes the range to each reference communication device using a timing delay determined from the internal delay calibration performed by each reference communication device.

26. The system of claim 18, wherein:

said mobile communication device comprises a clock adapted to maintain a local timing reference, said mobile communication device determining a time of transmission of each outbound ranging signal and a time of arrival of each reply ranging signal in accordance with the local timing reference; and

each reference communication device comprises a clock adapted to maintain a local timing reference that is not synchronized with the local timing reference of the clock of said mobile communication device, each reference communication device determining a time of arrival of each outbound ranging signal and a time of transmission of each reply ranging signal in accordance with the local timing reference of the reference communication device.

27. The system of claim 26, wherein the clock of said mobile communication device and the clock of each of said reference communication devices are low accuracy clocks.

28. The system of claim 18, wherein said outbound ranging signals and said reply ranging signals are spread spectrum signals.

29. The system of claim 18, wherein each reference communication device is one of:

a fixed communication device permanently mounted at a known position; and

another mobile communication device.

30. The system of claim 29, wherein at least one of said reference communication devices is another mobile communication device.

31. The system of claim 18, wherein said mobile communication device is capable of varying which among a set of communication devices serve as said reference communication devices.

32. The system of claim 18, wherein:

said outbound ranging signals and said reply ranging signals include an acquisition portion; and

said mobile communication device and each reference communication device include a two-stage signal acquisition processor adapted to determine the time of arrival (TOA) of each reply ranging signal and each outbound ranging signal, respectively, said two-stage signal acquisition processor including a detection processor for detecting the acquisition portion and a TOA synchronization processor for accurately determining the time of arrival from the acquisition portion, said detection processor triggering operation of said TOA synchronization processor.

33. The system of claim 32, wherein the acquisition portion includes a communication acquisition sequence and a TOA synchronization sequence, wherein said detection processor operates on the communication acquisition sequence, and the TOA synchronization processor operates on the TOA synchronization sequence.

34. A method of determining the range between a mobile communication device and a reference communication device, comprising the steps of:

(a) transmitting a sequence of outbound ranging signals at different carrier frequencies from the mobile communication device to the reference communication device;

(b) transmitting a sequence of reply ranging signals at the different carrier frequencies from the reference communication device to the mobile communication device in response to the outbound ranging signals;

(c) Doppler compensating the reply ranging signals to reduce errors in estimating the time of arrival of the reply ranging signals; and

(d) determining the range between the mobile communication device and the reference communication device from a round-trip signal propagation time of a selected outbound ranging signal and a corresponding reply ranging signal transmitted at a carrier frequency providing a highest signal timing accuracy.

35. The method of claim 34, wherein steps (a), (b) and (c) are repeated with the mobile communication device and a plurality of reference communication devices, the method further comprising the step of:

(d) determining the position of the mobile communication device from known positions of the reference communication devices and the range to each reference communication device.

36. The method of claim 34, wherein step (c) includes:

(c1) determining a time of transmission of each outbound ranging signal and a time of arrival of each reply ranging signal in accordance with a local timing reference of the mobile communication device; and

(c2) determining a time of arrival of each outbound ranging signal and a time of transmission of each reply ranging signal in accordance with a local timing reference of the reference communication device that is not synchronized with the local timing reference of the local timing reference of the mobile communication device.

37. The method of claim 36, wherein the mobile communication device and the reference communication device maintain local timing references using low accuracy clocks.

38. The method of claim 34, wherein steps (a) and (b) including transmitting the outbound ranging signals and the reply ranging signals as spread spectrum signals.

39. The method of claim 34, further comprising the steps of:

(d) performing internal delay calibration to estimate internal transmitter and receiver timing delays in the mobile communication device and in the reference communication device, wherein step (c) includes using the estimated internal transmitter and receiver timing delays in the mobile communication device and in the reference communication device to determine the range.

40. The method of claim 34, wherein step (c) further includes:

(c1) determining a time of arrival of each reply ranging signal at said mobile communication device using a leading edge curve fit; and

(c2) determining a time of arrival of each outbound ranging signal at each reference communication device using a leading edge curve fit.

41. The method of claim 34, wherein each reply ranging signal includes an acquisition portion, and step (c) further includes determining a time of arrival (TOA) of the reply ranging signal at the mobile communication unit using a two-stage process, including detection of the acquisition portion and TOA synchronization for accurately determining the time of arrival from the acquisition portion, wherein detection of the acquisition portion triggers TOA synchronization.

42. The method of claim 41, wherein the acquisition portion includes a communication acquisition sequence and a TOA synchronization sequence, wherein step (c) includes detecting the communication acquisition sequence and performing TOA synchronization on the TOA synchronization sequence.

43. A mobile communication device capable of determining range to a reference communication device by exchanging ranging signals with the reference communication device, comprising:

a transmitter configured to transmit to the reference communication device a sequence of outbound ranging signals at different carrier frequencies;

a receiver configured to receive from the reference communication device a sequence of reply ranging signals at the different carrier frequencies in response to the outbound ranging signals; and

a processor configured to rotate a phase of each reply ranging signal to incremental phase angles over a range of phase angles and to select from among the reply ranging signals at each carrier frequency and incremental phase angle a reply ranging signal providing a highest signal timing accuracy, said processor determining a time of arrival of the selected reply ranging signal and the range to the reference communication device from a round-trip signal propagation time of the selected reply ranging signal and a corresponding outbound ranging signal.