Collision arbitration method and apparatus for reading multiple frequency identification tags

Abstract

A method for simultaneously reading a serial number and / or other information from multiple colliding RF signals from RF identification tags (1-5) requires minimal additional logic in the tag's processor and provides for a powerful and rapid sorting and identification scheme. This technique employs a primary communication channel and multiple secondary channels, A locator or reader unit (6) interrogates the tags (1-5), which respond with an RF signal. Upon receiving multiple signals, the locator or reader unit (6) commands the RFID tags (1-5) and requires them to transmit another response, which is transmitted in one of the secondary channels based on a portion of their unique serial identification number, thereby forcing the tags (1-5) to sort in the secondary channels. These secondary channels are assigned using a portion of the unique serial identification numbers for the tags. The reader (6) then detects an acknowledgment in the occupied secondary channels and commands a tag (1-5) in a particular channel to move to the primary channel. Once the signal is transmitted in the primary channel, the reader (6) reads the identification number. If there is further collision, the collided tags are returned to the secondary channel and sorted again using a different portion of their ID number. This process continues until all the tags (1-5) are sorted and identified. Once the tags (1-5) are all sorted, the tags (1-5) are assigned yet another channel distinct from the secondary channels that are used for sorting.

Description

Background of the invention [0001] The present invention relates generally to methods and apparatus for resolving conflicts arising from simultaneously receiving data transmissions, and more particularly to methods and apparatus for resolving conflicts arising from simultaneously receiving data transmissions from multiple sensors. [0002] RF identification tags have many applications, including but not limited to personal identification, utility line marking, object tracking, and more. When communicating over wireless methods (or public lines), it is necessary to resolve potential collisions or contentions due to simultaneous reading of multiple units. Each such system requires a master transmit / receive unit to discriminate between potentially multiple tags. Simultaneous reception of multiple transmissions requires the master transmit / receive unit to sort transmission conflicts by interrogating (eg sending) multiple times and further processing the received signal. [0003]...

AI Technical Summary

Problems solved by technology

[0019] The complex application of each of the above patents reduces the stability of the sign, which is critical for a device expected to last for 50 years

Also, the data speeds used in underground signs are relatively low (around 125Hz) to guarantee proper reception

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