Method and apparatus to manage RFID tags

Abstract

A method of establishing wireless communications between an interrogator and individual ones of multiple wireless identification devices, the method comprising utilizing a tree search method to establish communications without collision between the interrogator and individual ones of the multiple wireless identification devices, a search tree being defined for the tree search method, the tree having multiple levels representing subgroups of the multiple wireless identification devices, the number of devices in a subgroup in one level being half of the number of devices in the next higher level, the tree search method employing level skipping wherein at least one level of the tree is skipped. A communications system comprising an interrogator, and a plurality of wireless identification devices configured to communicate with the interrogator in a wireless fashion, the respective wireless identification devices having a unique identification number, the interrogator being configured to employ a tree search technique to determine the unique identification numbers of the different wireless identification devices so as to be able to establish communications between the interrogator and individual ones of the multiple wireless identification devices without collision by multiple wireless identification devices attempting to respond to the interrogator at the same time, wherein levels of the tree are occasionally skipped.RFID tags are managed by an interrogator. In one embodiment, the interrogator sends a first command indicating a first value and a first memory range, and a second command indicating second value and a second memory range. The first memory range differs from the second memory range by at least two bits. RFID tags compare the first and second values to corresponding values stored in the tags to determine if the tags are selected. Selected tags may respond to the interrogator with independently generated random numbers.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]ThisMore than one reissue application has been filed for the reissue of U.S. Pat. No. 6,307,848, which reissue applications are the initial, present reissue application Ser. No. 10 / 693,697 filed Oct. 23, 2003, a continuation reissue applciation Ser. No. 11 / 865,580 filed Oct. 1, 2007, a continuation reissue application Ser. No. 11 / 865,584 filed Oct. 1, 2007, and a further continuation reissue application Ser. No. 12 / 604,329 filed Oct. 22, 2009, where the present application is a Continuationreissue application of U.S. Pat. No. 6,307,848, issued from U.S. patent application Ser. No. 09 / 773,461, filed Jan. 31, 2001, which is a continuation application of U.S. patent application Ser. No. 09 / 551,304, filed Apr. 18, 2000, <?delete-start id="DEL-S-00004" date="20110510" ?>and<?delete-end id="DEL-S-00004" ?> titled “Method of Addressing Messages, and Establishing Communications Using a Tree Search Technique That Skips Levels” <?in...

AI Technical Summary

Benefits of technology

[0016]One aspect of the invention provides a radio frequency identification device comprising an integrated circuit including a receiver, a transmitter, and a microprocessor. In one embodiment, the integrated circuit is a monolithic single die single metal layer integrated circuit including the receiver, the transmitter, and the microprocessor. The device of this embodiment includes an active transponder, instead of a transponder which relies on magnetic coupling for power, and therefore has a much greater range.

Problems solved by technology

As large numbers of objects are moved in inventory, product manufacturing, and merchandising operations, there is a continuous challenge to accurately monitor the location and flow of objects.

However, such identification systems are only capable of operation over a relatively short range, limited by the size of a magnetic field used to supply power to the devices and to communicate with the devices.

When the interrogator sends a message to a transponder device requesting a reply, there is a possibility that multiple transponder devices will attempt to respond simultaneously, causing a collision, and thus causing an erroneous message to be received by the interrogator.

For example, if the interrogator sends out a command requesting that all devices within a communications range identify themselves, and gets a large number of simultaneous replies, the interrogator may not be able to interpret any of these replies.

A problem with the Aloha scheme is that if there are many devices, or potentially many devices in the field (i.e. in communications range, capable of responding) then there must be many available slots or many collisions will occur.

This results in the system slowing down significantly because the reply time equals the number of slots multiplied by the time period required for one reply.

Images