Methods and apparatus for determining the time of arrival of a signal

• US 6,665,333 B2
• Filed: 04/29/2002
• Issued: 12/16/2003
• 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., Doyle, Lawrence J., Forstrom, Howard
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Lugo, David B.
• Application Number:
  US10/133,368
• Publication Number:
  US 20020118723A1
• Time in Patent Office: 596 Days
• Field of Search: 375/130, 375/140, 375/141, 375/142, 375/143, 375/146, 375/147, 375/152, 375/316, 375/340
• US Class Current: 375/147
• 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 carrier signal having signal acquisition information embedded therein for determining a time of arrival of the carrier signal, comprising:

a first sequence comprising a plurality of first spread spectrum symbols for detecting arrival of the carrier signal, each of said first spread spectrum symbols comprising a plurality of chips; and

a second sequence comprising at least one spread spectrum symbol for determining a time of arrival of the carrier signal, said at least one spread spectrum symbol comprising a greater number of chips than each of said first spread spectrum symbols.

2. The carrier signal of claim 1, wherein said at least one spread spectrum symbol of said second sequence comprises a greater number of chips than a sum of the chips of all of said first spread spectrum symbols.

3. The carrier signal of claim 1, wherein said second sequence comprises a greater number of chips than said first sequence.

4. The carrier signal of claim 1, wherein said carrier signal is configured to be used in a communication system employing a carrier sense multiple access—

collision avoidance (CSMA-CA) messaging protocol.

5. The carrier signal of claim 1, further comprising a data portion.

15. The carrier signal of claim 1, wherein the carrier signal, including the first and second sequences, has a predetermined bandwidth.

16. The carrier signal of claim 1, wherein the first and second sequences have a same chip rate.

17. The carrier signal of claim 1, wherein said carrier signal is configured to be used in a communication system employing a round-trip ranging scheme.

6. A method of acquiring a transmitted signal including a first acquisition portion and a second acquisition portion, comprising:

(a) detecting arrival of the transmitted signal from the first acquisition portion, wherein the first acquisition portion comprises a plurality of first spread spectrum symbols each including a plurality of chips; and

(b) determining a time of arrival of the transmitted signal from the second acquisition portion in response to detecting arrival of the transmitted signal, wherein the second acquisition portion comprises at least one spread spectrum symbol including a greater number of chips than each of the first spread spectrum symbols.

7. The method of claim 6, wherein (a) includes applying a first digital matched filter to the first acquisition portion, and (b) includes applying a second digital matched filter, of a greater length than the first digital matched filter, to the second acquisition portion.

8. The method of claim 6, wherein a determination of the time of arrival of the transmitted signal is attempted only in response to being triggered by detection of an arrival of the transmitted signal.

18. The method of claim 6, wherein the transmitted signal, including the first and second acquisition portions, has a predetermined bandwidth.

19. The method of claim 6, wherein the first and second acquisition portions have a same chip rate.

20. The method of claim 6, wherein the transmitted signal is received in accordance with a carrier sense multiple access—

collision avoidance (CSMA-CA) messaging protocol.

21. The method of claim 6, wherein the transmitted signal is received in accordance with a round-trip ranging scheme.

9. An apparatus for detecting a transmitted signal including a first acquisition portion and a second acquisition portion, comprising:

an acquisition processor configured to detect an arrival of the first acquisition portion of the transmitted signal, wherein the first acquisition portion comprises a plurality of first spread spectrum symbols each including a plurality of chips; and

a time of arrival processor configured to determine a time of arrival of the transmitted signal from the second acquisition portion in response to detection of the first acquisition portion, wherein the second acquisition portion comprises at least one spread spectrum symbol including a greater number of chips than each of the first spread spectrum symbols.

10. The apparatus of claim 9, wherein said time of arrival processor determines the time of arrival of the transmitted signal with a greater accuracy than said acquisition processor.

11. The apparatus of claim 9, wherein said acquisition processor comprises a digital matched filter of a first length and said time of arrival processor comprises a digital matched filter of a second length greater than the first length.

12. The apparatus of claim 9, wherein said time of arrival processor determines the time of arrival of the transmitted signal only in response to said acquisition processor detecting an arrival of the transmitted signal.

13. The apparatus of claim 9, wherein said acquisition processor triggers said time of arrival processor to determine the time of arrival of the transmitted signal.

14. The apparatus of claim 9, wherein said apparatus is a mobile communication device.

22. The apparatus of claim 9, wherein the transmitted signal, including the first and second acquisition portions, has a predetermined bandwidth.

23. The apparatus of claim 9, wherein the first and second acquisition portions have a same chip rate.

24. The apparatus of claim 9, wherein the apparatus receives the transmitted signal in accordance with a carrier sense multiple access—

collision avoidance (CSMA-CA) messaging protocol.

25. The apparatus of claim 9, wherein the apparatus receives the transmitted signal in accordance with a round-trip ranging scheme.