Method of addressing messages and communications systems

Abstract

A method ofand apparatus for 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 respectively representing subgroups of the multiple wireless identification devices, the method further comprising starting the tree search at a selectable level of the search tree. 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 the interrogator is configured to start the tree search at a selectable level of the search treeThe interrogator transmits an initial wireless command to start identification of the wireless identification devices. The initial wireless command specifies at least two bits and requesting first devices having the at least two bits to reply. If there is no collision in response to the initial wireless command, the interrogator identifies, from a response to the initial command, a random number generated at one of the devices.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]ThisMore than one reissue application has been filed for the reissue of U.S. Pat. No. 6,307,847, including the initial reissue application Ser. No. 10 / 693,696, filed Oct. 23, 2003, a continuation reissue application Ser. No. 11 / 859,364, filed Sep. 21, 2007, a continuation reissue application Ser. No. 12 / 493,542, filed Jun. 29, 2009, and the present continuation reissue application, which is a continuation application of U.S. patent application Ser. No. 10 / 693,696, filed Oct. 23, 2003 and titled “Method and Apparatus to Select Radio Frequency Identification Devices in Accordance With an Arbitration Scheme”, which is a reissue application of U.S. Pat. No. 6,307,847, issued from U.S. patent application Ser. No. 09 / 617,390, filed Jul. 17, 2000 and titled “Method of Addressing Messages and Communications System”, which is a Continuationcontinuation application of U.S. patent application Ser. No. 09 / 026,043, filed Feb. 19, 1998, and titled “Meth...

AI Technical Summary

Benefits of technology

This approach enables efficient communication with individual RFID devices without collisions, reducing arbitration time and conserving battery life by determining the optimal starting level for the tree search, thereby improving system performance and reducing power consumption.

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.

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