Extensible object location system and method using multiple references

• US 7,710,322 B1
• Filed: 01/13/2006
• Issued: 05/04/2010
• Est. Priority Date: 05/10/2005
• Status: Active Grant

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: Multispectral Solutions Incorporated (Zebra Technologies Corporation)
• Inventors: Chen, Keming, Richley, Edward A., Fontana, Robert J., Turner, Belinda, Ameti, Aitan
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Nguyen; Nga X
• Application Number:
  US11/331,229
• Time in Patent Office: 1,572 Days
• Field of Search: 342459-465
• US Class Current: 342/465
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/02213 Receivers arranged in a network for determining the position of a transmitter
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308

Abstract

An ultra wideband (UWB) or short-pulse RF system is disclosed that can be used to precisely locate or track objects (such as personnel, equipment, assets, etc.) in real-time in an arbitrarily large, physically connected or disconnected, multipath and/or noisy environment. A system implementation includes multiple zones or groups of receivers that receives RF signals transmitted by one or more timing reference tags and one or more objects having associated object tags. Each zone or group may share a common receiver. By combining a multiple reference tag system with a virtual group of receivers, i.e., a zoning technique or system, a cost-effective system can be provided that offers scalability and flexibility to monitor a significantly expanded coverage area.

Claims

1. A system to determine a position of an object having an associated object tag that transmits an RF signal from any one of multiple zones of a region, said system comprising:

respective receiver groups of said multiple zones that each include multiple receivers wherein at least one of said receivers of one zone is shared with a receiver group of at least one other zone,

a timer associated with each receiver to detect an arrival time of an RF signal,

a clock source to enable synchronization of time indications of each said timer,

a reference tag transmitter associated with each receiver group of a zone to transmit an RF reference signal from a known location within said zone, and

a processing hub in communication with said receivers to determine the position of the object according to synchronization of said common clock source and time differences of arrival of RF signals transmitted by said object tag at respective receivers of a receiver group of any one of said multiple zones.

2. The system of claim 1 wherein said clock source is common and includes a daisy-chained cable to convey clock signals to the receivers and said processing hub includes a data cable to convey digital representations of said time differences of arrival of said RF signals.

3. The system of claim 2, wherein said object tag and reference tags transmit ultra wideband signals and said receivers comprise ultra wideband receivers.

4. The system according to claim 3 wherein said timers comprise digital counters that are synchronized in frequency, but not necessarily in phase, by said common clock source.

5. The system according to claim 4, wherein said processing hub determines the position of the object according to relative phase offsets of said counters.

6. The system according to claim 5, wherein the receiver groups are arranged in a pattern to define a matrix of rows and columns of zones.

7. The system according to claim 5, wherein said receivers and said reference tags are arranged substantially in a ring configuration to at least partially encircle a region within which to detect an object having said associated object tag.

8. The system according to claim 5 wherein said reference tags transmit an ID code to distinguish among multiple ones of said reference tags when determining object location according to time differences of arrival.

9. The system according to claim 5, wherein said processor determines an offset of a timer in a group according to offsets of other timers in a contiguous group having said shared receiver.

10. A method of determining a position of an object having an associated object tag that transmits an RF object tag signal, said method comprising the steps of:

providing respective groups of receivers to define respective zones in a monitored region in which to detect said object,

positioning a receiver of one group in sharing relation with a receiver of another group so that said receiver resides in two groups of receivers,

providing a reference tag in each said zone to transmit a reference signal,

transmitting said reference signal from a fixed location in each said zone,

in each said zone, receiving the reference signal at each receiver of said group of receivers to determine a time synchronization among the receivers of said group,

transmitting an object tag signal within a zone,

receiving the object tag signal at the receivers of a group of receivers of said zone, and

computing object location based on said time synchronization and time of arrival differences of said object tag signal at multiple receivers within a zone whereby to provide an object location system having a reduced number of receivers.

11. The method of claim 10, wherein said receiving step further includes indexing a cyclic timing circuit using a common clock source to produce unitary increments of time indicative of said timing offset.

12. The method of claim 10, further comprising:

arranging said zones in a pattern of rows and columns wherein contiguous rows and/or contiguous columns share receivers.

13. The method of claim 10, further comprising:

arranging said zones to define around an RF barrier within a monitored region.

14. The method of claim 10, further comprising:

in said determining step, utilizing timing offset information to discriminate against unwanted reflected signals within a zone.