RFID loss-prevention using angle-of-arrival
First Claim
1. A method for a Radio-Frequency Identification (RFID) system having first, second, and third noncollinear receivers to determine a distance to an RFID tag, the method comprising:
- transmitting a first command;
receiving in the first receiver a first tag reply, in the second receiver a second tag reply, and in the third receiver a third tag reply;
determining that the first, second, and third tag replies are phase-shifted versions of a single initial reply from the RFID tag responding to the first command;
determining, from at least a first phase difference between the first and second tag replies, a first tag read angle;
determining, from at least a second phase difference between the first and third tag replies, a second tag read angle;
determining, from at least a third phase difference between the second and third tag replies, a third tag read angle; and
determining, from the first, second, and third tag read angles, the distance to the RFID tag.
1 Assignment
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Accused Products
Abstract
An RFID loss-prevention system (LPS) permits authorized items to leave a facility and may perform a security action if an unauthorized item leaves the facility. A checkout reader first authorizes an item tagged with an RFID tag to exit a facility by reading an identifier from the tag, obtaining an exit authorization, and sending the identifier to a database. A reader system configured to direct at least two beams along a facility exit path reads tagged items exiting the facility, determines at least one of a travel direction and a tag location, and uses the determination to indicate that a tag is exiting or has exited the facility. The LPS then uses the database to determine if the exiting/exited tag is authorized to leave the facility.
23 Citations
20 Claims
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1. A method for a Radio-Frequency Identification (RFID) system having first, second, and third noncollinear receivers to determine a distance to an RFID tag, the method comprising:
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transmitting a first command; receiving in the first receiver a first tag reply, in the second receiver a second tag reply, and in the third receiver a third tag reply; determining that the first, second, and third tag replies are phase-shifted versions of a single initial reply from the RFID tag responding to the first command; determining, from at least a first phase difference between the first and second tag replies, a first tag read angle; determining, from at least a second phase difference between the first and third tag replies, a second tag read angle; determining, from at least a third phase difference between the second and third tag replies, a third tag read angle; and determining, from the first, second, and third tag read angles, the distance to the RFID tag. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for a multi-receiver Radio-Frequency Identification (RFID) system to locate an RFID tag, the method comprising:
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transmitting a first command; in response to transmitting the first command, receiving first, second, and third tag replies; determining that the first, second, and third tag replies are phase-shifted versions of a single initial reply from the RFID tag responding to the first command; determining, from at least a first phase difference between the first and second tag replies, a first tag read angle; determining, from at least a second phase difference between the first and third tag replies, a second tag read angle; determining, from at least a third phase difference between the second and third tag replies, a third tag read angle; and determining, from the first, second, and third tag read angles, an initial location of the RFID tag. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A Radio-Frequency Identification (RFID) system configured to locate an RFID tag, the system comprising:
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a reader system configured to; transmit a first command; in response to transmitting the first command, receive first, second, and third tag replies; and a processor module coupled to the reader system and configured to; determine that the first, second, and third tag replies are phase-shifted versions of a single initial reply from the RFID tag responding to the first command; determine, from at least a first phase difference between the first and second tag replies, a first tag read angle; determine, from at least a second phase difference between the first and third tag replies, a second tag read angle; determine, from at least a third phase difference between the second and third tag replies, a third tag read angle; and determine, from the first, second, and third tag read angles, an initial location of the RFID tag. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification