Method and apparatus for determining the position of a mobile communication device using low accuracy clocks

• US 6,453,168 B1
• Filed: 08/02/1999
• Issued: 09/17/2002
• Est. Priority Date: 08/02/1999
• Status: Expired due to Term

• Current Assignee: Stingray IP Solutions LLC (Acacia Research Corporation)
• Original Assignee: ITT Manufacturing Enterprises, Inc. (ITT, Inc.)
• Inventors: McCrady, Dennis D., Doyle, Lawrence J., Forstrom, Howard
• Primary Examiner(s): Trost, William
• Assistant Examiner(s): SOBUTKA, PHILIP
• Application Number:
  US09/365,702
• Time in Patent Office: 1,142 Days
• Field of Search: 455/456, 455/457, 455/422, 455/517, 455/466, 455/67.1, 455/65, 455/59, 455/504, 455/506, 455/133-5, 455/277.1, 455/277.2, 342/457, 342/463, 342/357.06, 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 spread spectrum 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 messages is accurately determined to yield the range estimates required to calculate the position of the mobile radio via trilateration. The master radio transmits outbound ranging messages to plural reference radios which respond by transmitting reply ranging messages. Upon reception of the reply ranging message, the master radio determines the range to the reference radio from the signal propagation time calculated by subtracting the far-end turn around time from the round-trip elapsed time. Any combination of fixed or mobile radios of known positions can be used as the reference radios for another mobile radio in the system, thereby providing adaptability under varying transmission conditions. The individual radios do not need to be synchronized to a common time reference, thereby eliminating the need for highly accurate system clocks. By performing internal delay calibration, errors caused by difficult-to-predict internal transmitter and receiver delay variations can be minimized. Leading-edge-of-the-signal curve fitting and frequency diversity techniques minimize the effects of multipath interference on TOA estimates.

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.

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 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.

4. The mobile communication device of claim 3, 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.

5. 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.

6. The mobile communication device of claim 5, 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.

7. 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.

8. 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.

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

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

means for transmitting to the reference communication device a sequence of outbound ranging signals at different carrier frequencies;

means for receiving from the reference communication device a sequence of reply ranging signals at the different carrier frequencies in response to the outbound ranging signals;

means for selecting from among the reply ranging signals a reply ranging signal at a carrier frequency providing a highest signal timing accuracy; and

means for 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.

11. The mobile communication device of claim 10, wherein said selecting means selects the reply ranging signal whose carrier frequency minimizes multipath interference.

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

means for 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.

13. 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; and

(c) 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.

14. The method of claim 13, 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.

15. The method of claim 13, wherein the selected outbound ranging message and the corresponding reply ranging message are selected to minimizes multipath interference.

16. 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, 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.

17. The system of claim 16, wherein, for each reference radio, said mobile communication device selects the reply ranging signal whose carrier frequency minimizes multipath interference.

18. The system of claim 16, wherein at least one of said reference communication devices is another mobile communication device.