System for and method of accurately determining true bearings of radio frequency identification (RFID) tags associated with items in a controlled area

• US 9,477,865 B2
• Filed: 12/13/2013
• Issued: 10/25/2016
• Est. Priority Date: 12/13/2013
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Inventors: Koch, Michael J, Bekritsky, Benjamin J, Jacques, Alexander M, Swope, Charles B
• Primary Examiner(s): HOLLOWAY III, EDWIN C
• Application Number:
  US14/106,368
• Publication Number:
  US 20150169910A1
• Time in Patent Office: 1,047 Days
• Field of Search: 340/10.1
• US Class Current: 1/1
• CPC Class Codes: G01S 13/75 using transponders powered from received waves, e.g. using passive transponders , or using passive reflectors
• CPC Class Codes: G01S 13/751 wherein the responder or reflector radiates a coded signal
• CPC Class Codes: G01S 13/825 with exchange of information between interrogator and responder
• CPC Class Codes: G01S 3/16 using amplitude comparison of signals derived sequentially from receiving antennas or antenna systems having differently-oriented directivity characteristics or from an antenna system having periodically-varied orientation of directivity characteristic
• CPC Class Codes: G01S 3/46 using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
• CPC Class Codes: G06K 7/10099 the directional field being used for pinpointing the location of the record carrier, e.g. for finding or locating an RFID tag amongst a plurality of RFID tags, each RFID tag being associated with an object, e.g. for physically locating the RFID tagged object in a warehouse
• CPC Class Codes: G06K 7/10128 the step consisting of detection of the presence of one or more record carriers in the vicinity of the interrogation device
• CPC Class Codes: G06K 7/10366 the interrogation device being adapted for miscellaneous applications
• CPC Class Codes: G06K 7/10415 the interrogation device being fixed in its position, such as an access control device for reading wireless access cards, or a wireless ATM banking machines in general G07F19/00

Abstract

A radio frequency (RF) identification (RFID) tag reading system and method accurately determine true bearings of RFID tags associated with items in a controlled area. An RFID reader has an array of antenna elements and a plurality of RF transceivers. A controller controls the transceivers by steering a primary transmit beam over the controlled area by transmitting a primary transmit signal to each tag, and steering a primary receive beam at a primary steering angle by receiving a primary receive signal from each tag. The controller thereupon steers a plurality of secondary receive offset beams at different secondary steering angles that are offset from the primary steering angle by receiving secondary receive offset signals from each tag, and by processing the offset signals to determine a true bearing for each tag.

Claims

1. A radio frequency (RF) identification (RFID) tag reading system for accurately determining true bearings of RFID tags associated with items in a controlled area, comprising:

an RFID reader having an array of antenna elements and a plurality of RF transceivers; and

a controller operatively connected to the transceivers, and operative for controlling the transceivers by executing a tag processing module operative for steering a primary transmit beam over the controlled area by transmitting a primary transmit signal via the antenna elements to each tag, and for steering a primary receive beam at a primary steering angle by receiving a primary receive signal via the antenna elements from each tag, and

the controller being further operative for controlling the transceivers by executing a bearing processing module operative for steering a plurality of secondary receive offset beams at different secondary steering angles that are offset from the primary steering angle by receiving at least four secondary receive offset signals from at least four antenna elements from each tag, and by processing the at least four secondary receive offset signals to determine a true bearing for each tag.

2. The system of claim 1, wherein the tag processing module is operative during a coarse scan, and wherein the bearing processing module is operative during a fine scan.

3. The system of claim 1, wherein the bearing processing module is operative for steering a first pair of the secondary receive offset beams at opposite sides of the primary receive beam in elevation, and for processing a first pair of the secondary receive offset signals to obtain a pair of elevation offset signals;

and wherein the bearing processing module is further operative for steering a second pair of the secondary receive offset beams at opposite sides of the primary receive beam in azimuth, and for processing a second pair of the secondary receive offset signals to obtain a pair of azimuth offset signals.

4. The system of claim 3, wherein the bearing processing module is operative for processing the elevation offset signals by dividing their difference by their sum to obtain an elevation error signal as an elevation correction to the primary steering angle, and wherein the bearing processing module is operative for processing the azimuth offset signals by dividing their difference by their sum to obtain an azimuth error signal as an azimuth correction to the primary steering angle.

5. The system of claim 1, wherein the bearing processing module is operative for steering each secondary receive offset beam by receiving the secondary receive offset signals over a plurality of channels;

and further comprising, on each channel, a complex multiplier and a programmable device for setting a complex coefficient for the complex multiplier to introduce a weighting factor on each channel to effect steering.

6. The system of claim 1, and a server operatively connected to the RFID reader, and wherein the bearing processing module is implemented in at least one of the RFID reader and the server.

7. The system of claim 1, wherein the bearing processing module is operative for steering the offset beams in at least one of a sequential and a simultaneous manner.

8. A radio frequency (RF) identification (RFID) tag reading system for accurately determining true bearings of RFID tags associated with items in a controlled area, comprising:

an RFID reader mounted in an overhead location in the controlled area, and having an array of antenna elements and a plurality of RF transceivers;

a server operatively connected to the RFID reader; and

a controller located in at least one of the RFID reader and the server and operatively connected to the transceivers, the controller being operative for controlling the transceivers by executing a tag processing module operative for steering a primary transmit beam over the controlled area by transmitting a primary transmit signal via the antenna elements to each tag, and for steering a primary receive beam at a primary steering angle by receiving a primary receive signal via the antenna elements from each tag, and

the controller being further operative for controlling the transceivers by executing a bearing processing module operative for steering a plurality of secondary receive offset beams at different secondary steering angles that are offset from the primary steering angle by receiving at least four secondary receive offset signals from at least four antenna elements from each tag, and by processing the at least four secondary receive offset signals to determine a true bearing for each tag.

9. The system of claim 8, wherein the tag processing module is operative during a coarse scan, and wherein the bearing processing module is operative during a fine scan.

10. The system of claim 8, wherein the bearing processing module is operative for steering a first pair of the secondary receive offset beams at opposite sides of the primary receive beam in elevation, and for processing a first pair of the secondary receive offset signals to obtain a pair of elevation offset signals;

and wherein the bearing processing module is further operative for steering a second pair of the secondary receive offset beams at opposite sides of the primary receive beam in azimuth, and for processing a second pair of the secondary receive offset signals to obtain a pair of azimuth offset signals.

11. The system of claim 10, wherein the bearing processing module is operative for processing the elevation offset signals by dividing their difference by their sum to obtain an elevation error signal as an elevation correction to the primary steering angle, and wherein the bearing processing module is operative for processing the azimuth offset signals by dividing their difference by their sum to obtain an azimuth error signal as an azimuth correction to the primary steering angle.

12. The system of claim 8, wherein the bearing processing module is operative for steering each secondary receive offset beam by receiving the secondary receive offset signals over a plurality of channels;

and further comprising, on each channel, a complex multiplier and a programmable device for setting a complex coefficient for the complex multiplier to introduce a weighting factor on each channel to effect steering.

13. A radio frequency (RF) identification (RFID) tag reading method of accurately determining true bearings of RFID tags associated with items in a controlled area, comprising:

mounting an RFID reader having an array of antenna elements and a plurality of RF transceivers, in the controlled area;

controlling the transceivers by having a controller execute a tag processing module operative for steering a primary transmit beam over the controlled area by transmitting a primary transmit signal via the antenna elements to each tag, and for steering a primary receive beam at a primary steering angle by receiving a primary receive signal via the antenna elements from each tag; and

controlling the transceivers by having the controller execute a bearing processing module operative for steering a plurality of secondary receive offset beams at different secondary steering angles that are offset from the primary steering angle by receiving at least four secondary receive offset signals from at least four antenna elements from each tag, and by processing the at least four secondary receive offset signals to determine a true bearing for each tag.

14. The method of claim 13, wherein the tag processing module is operative during a coarse scan, and wherein the bearing processing module is operative during a fine scan.

15. The method of claim 13, wherein the steering of a first pair of the secondary receive offset beams is performed at opposite sides of the primary receive beam in elevation, and wherein the processing of a first pair of the secondary receive offset signals is performed to obtain a pair of elevation offset signals;

and wherein the steering of a second pair of the secondary receive offset beams is performed at opposite sides of the primary receive beam in azimuth, and wherein the processing of a second pair of the secondary receive offset signals is performed to obtain a pair of azimuth offset signals.

16. The method of claim 15, wherein the processing of the elevation offset signals is performed by dividing their difference by their sum to obtain an elevation error signal as an elevation correction to the primary steering angle, and wherein the processing of the azimuth offset signals is performed by dividing their difference by their sum to obtain an azimuth error signal as an azimuth correction to the primary steering angle.

17. The method of claim 13, wherein the steering of each secondary receive offset beam is performed by receiving the secondary receive offset signals over a plurality of channels;

and introducing a weighting factor on each channel to effect steering.

18. The method of claim 13, and operatively connecting a server to the RFID reader, and implementing the bearing processing module in at least one of the RFID reader and the server.

19. The method of claim 13, wherein the steering of the offset beams is performed in at least one of a simultaneous and a sequential manner.

20. The method of claim 14, and creating a list of the tags in the controlled area during the coarse scan, and wherein the steering of the offset beams is performed for each listed tag.