Method, system, and apparatus for remote timing calibration of a RFID tag population

Abstract

A method, system, and apparatus for a timing subsystem in a radio frequency identification tag device are described. The timing subsystem provides a system oscillator or clock for the tag. The timing subsystem also provides frequencies used by an RF interface of the tag to generate backscatter modulated symbols. The timing subsystem also provides for oscillator calibration. The tag receives one or more oscillator calibration waveforms transmitted by a reader. The timing subsystem in the tag uses the oscillator calibration waveforms to successively adjust the frequency of the tag oscillator to a frequency desired by the reader. Hence, the reader may increase or decrease the oscillator frequency in the tag depending on the particular application. Furthermore, the reader may adjust the oscillator frequency for all tags in a population of tags using a single transmission of the one or more oscillator calibration waveforms.

Description

[0001] This application claims the benefit of U.S. Provisional Application No. 60 / 267,713, filed Feb. 12, 2001, which is herein incorporated by reference in its entirety.[0002] 1. Field of the Invention[0003] The present invention relates generally to radio frequency identification (RFID) tags.[0004] 2. Description of the Related Art[0005] Many product-related and service-related industries entail the use and / or sale of large numbers of useful items. In such industries, it may be advantageous to have the ability to monitor the items that are located within a particular range. For example, within a particular store, it may be desirable to determine the presence of inventory items located on the shelf, and that are otherwise located in the store.[0006] A device known as an RFID "tag" may be affixed to each item that is to be monitored. The presence of a tag, and therefore the presence of the item to which the tag is affixed, may be checked and monitored by devices known as "readers." ...

AI Technical Summary

Benefits of technology

[0013] This collision free environment is based on a set of communications symbols that allows multiple symbol values to be transmitted simultaneously without interference between, or destruction of any of these symbols.

[0014] These simplified algorithms do not require complex circuitry and intense processing. Therefore, in addition to promoting increased data rates, these efficient algorithms also promote lower transistor counts, lower tag costs, and lower power consumption (which increases the range at which a reader and tag may communicate).

Problems solved by technology

For instance, currently available tags are relatively expensive.

Furthermore, currently available tags consume large amounts of power.

Currently available tag power schemes, which include individually tag-included batteries, are inefficient and expensive.

These inefficient power schemes also lead to reduced ranges over which readers may communicate with tags in a wireless fashion.

Still further, currently available readers and tags use inefficient interrogation protocols.

These inefficient protocols slow the rate at which a large number of tags may be interrogated.

Conventional algorithms interrogate RFID tags with highly complex algorithms that are less efficient.

Furthermore, the use of conventional algorithms often involves two or more RF transmissions colliding.

Collision resolution consumes time without conveying data, and mandates complexity in algorithms, circuit design, and transistor count.

However, this may also introduce a burden on the implementation to add functionality, memory, processing power, etc., in order to present information to the highest OSI model layers.

This may result in an orientation sensitivity for a tag antenna with respect to a reader antenna that can greatly reduce the operational distance for a non-optimum orientation.

This is not desirable to the majority of markets looking for RFID products.

Again, a similar problem exists in that the wider frequency agility of a given antenna design will reduce the gain, or collected energy of a single antenna.

Wafer fabrication process variations may cause performance differences between chips.

These high temperatures can cause standard polymers to degrade quickly as well as become very unstable to work with.

Non-conductive oxides are detrimental to RF (UHF) performance, as they can significantly cause an antenna to detune.

This pattern of bits that were received may actually have been noise or were noise affected.

This assumption has a chance of error, of course, and is determined statistically upon the randomness of noise.

For example, a single-bit pattern may be considered to have a 1 in 2 chance of being generated by noise, which is not generally acceptable in industry.

However, this process may be more affected by RF noise in the environment.

This may occur in a noisy transmission environment.

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