Real-time locating system and method using timing signal

• US 7,212,563 B2
• Filed: 05/03/2002
• Issued: 05/01/2007
• Est. Priority Date: 05/04/2001
• Status: Active Grant

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: Wherenet Corporation (Zebra Technologies Corporation)
• Inventors: Wohl, Michael A., Belcher, Donald K., Boyd, Robert W., Wisherd, David S.
• Primary Examiner(s): Fan; Chieh M.
• Assistant Examiner(s): Bolourchi; Nader
• Application Number:
  US10/138,795
• Publication Number:
  US 20020181565A1
• Time in Patent Office: 1,824 Days
• Field of Search: 340/572.1, 340/10, 340/825.49, 340/539.13, 342/450, 342/126, 455/343.2, 455/456.1, 375/130, 235/335
• US Class Current: 375/130
• CPC Class Codes: G01S 5/02216 Timing or synchronisation of the receivers
• CPC Class Codes: G01S 5/0226 Transmitters
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

A location system includes a plurality of signal readers for receiving signals from a wireless transmitter to be located. The signals include a wideband, spread spectrum signal and a timing marker appended a predetermined time in front of the wideband, spread spectrum signal for indicating the presence of the wideband, spread spectrum signal. A location processor is operatively coupled to the signal readers for detecting the timing markers of signals and responsive to a detection of a timing marker, correlating a signal as a first-to-arrive signal and conducting differentiation of first-to-arrive signals to locate a wireless transmitter.

Claims

1. A location system comprising:

a plurality of signal readers for receiving signals from a wireless transmitter to be located wherein each signal reader time-stamps a signal with a time-of-arrival time stamp, each one of said signals consisting of a wideband, spread spectrum signal as a location pulse consisting of identification data for an object to be located to which the wireless transmitter is attached and a timing marker appended a predetermined time in front of the location pulse for indicating the presence of the location pulse and wherein the timing marker is timed at a predetermined range in front of the location pulse corresponding to a predetermined propagation distance to establish a known period of time to aid in finding the location pulse wherein a sampling window for edge detection as a range gate is determined by the timing of the timing marker; and

a location processor operatively coupled to said signal readers for processing the wideband, spread spectrum signal and responsive to a detection of the signal, correlating a signal as a first-to-arrive signal based on a time-of-arrival time stamp and conducting differentiation of first-to-arrive signals to locate the wireless transmitter.

2. A location system according to claim 1, wherein said timing marker is timed about 80 to about 120 nanoseconds in front of the wideband, spread spectrum signal.

3. A location system according to claim 1, wherein said timing marker is generated by a wireless local area network transmission.

4. A location system according to claim 3, and further comprising an access point base station operative with the location processor and at least one signal reader.

5. A location system according to claim 1, wherein said location processor comprises a matched filter correlator.

6. A location system according to claim 5, wherein said matched filter correlator further comprises matched filter banks having parallel correlators that correlate a received communications signal with time offset versions of a reference spreading code.

7. A location system according to claim 1, wherein said location processor further comprises a plurality of processors for distributing processing capability.

8. A location system according to claim 1, wherein three signal readers are used for determining the location of the wireless transmitter.

9. A location system according to claim 1, wherein each signal reader comprises a plurality of mutually diverse antennas for detecting signals at each signal reader.

10. A location system according to claim 1, wherein each wireless transmitter comprises a tag transmitter that is coupled with the object to be located.