The present invention is directed, in general, to a system for discrimination between multiple surface acoustic wave (SAW) identification tags and, more specifically, to a reader and response control system for discrimination between multiple SAW identification tags and a method of operation thereof.
A number of different types of electronic identification methods and devices are currently being employed ranging from ubiquitous bar codes and magnetic strips to sophisticated radio frequency identification (xe2x80x9cRFIDxe2x80x9d) devices. In the case of bar codes and magnetic strips, a significant limiting factor is the relatively short effective range. Magnetic strips, for example, generally require the reader to be in direct contact with the strip in order to detect and decode any data. In those few cases where a magnetic strip is read with a device other than a direct contact reader, the effective reading range is still only a few centimeters at best. Similarly, the effective range for reliably reading bar codes is also typically no better than a few centimeters, at best. Because the range at which bar codes and magnetic strips can be read is so short, they are usually read one at a time and seldom does one bar code or magnetic strip interfere with another.
Most RFID tags can be conveniently divided into chip tags and chipless tags. Chipless tags generally have no longer a read range than bar codes or magnetic strips. Although prior art RFID chip tags can be fabricated that have a significantly longer reliable read range than chipless tags, magnetic strips or bar codes, they are generally so expensive that their use is generally limited to discrete applications where the expense can be justified economically. In most cases, these prior art RFID chip tags are individually read and little opportunity exists for tag responses to interfere with one another.
A recently developed RFID tag with a long read range that can be inexpensively fabricated requires the problem of interference from multiple tag responses to an interrogation signal to be addressed. A complete and detailed description of SAW identification tags 120 is set forth in detail in U.S. patent application Ser. No. 20030111540, entitled xe2x80x9cSurface Acoustic Wave Identification Tag Having Enhanced Data Content and Methods of Operation and Manufacture Thereof,xe2x80x9d Hartmann, Clinton S. (xe2x80x9cHartmann Onexe2x80x9d), commonly assigned with the invention and incorporated herein by reference. A description of SAW identification tag readers 130 to read such tags is described in detail in U.S. patent application Ser. No. 20030141366, entitled xe2x80x9cReader For a High Information Capacity Saw Identification Tag and Method of Use Thereof,xe2x80x9d Hartmann, Clinton S. (xe2x80x9cHartmann Threexe2x80x9d), also commonly assigned with the invention and incorporated herein by reference. Because such tags are inexpensive enough to be attached to a large number of objects (such as objects on a shipping pallet) and because they have sufficient range to permit a tag reader to interrogate a large number of tags at the same time, the signal interference or code collision problem caused by multiple responses must be addressed as well as any inter-symbol interference problems caused by so many responses being transmitted at one time. These issues need to be resolved before the full potential of SAW identification tags can be realized.
Accordingly, what is needed in the art are systems and methods that permit a user to reliably distinguish between multiple responses to an interrogation signal that are emanating from SAW tags that are in close proximity.
To address the above-discussed deficiencies of the prior art, the present invention provides a system for discriminating between coded responses from multiple SAW identification tags and a method of operating such system. In one embodiment the system provides for (1) a SAW tag reader subsystem that detects coded responses from the tags to an interrogation pulse; and (2) a coded response analyzing subsystem, coupled to the SAW tag reader subsystem, that employs signal processing techniques to separate portions of the coded responses and generates possibilities for remaining portions of such coded responses.
The present invention thus provides a system for distinguishing between multiple responses to an interrogation signal that emanate from SAW tags in close proximity where a xe2x80x9ccollisionxe2x80x9d exists between such responses in the signal processing sense of this term. The successful identification of a SAW tag requires that positive and reliable determination of the data encoded on a single SAW tag. Thus, it is essential that a SAW identification tag system be able to separate and identify the signature of a single tag from the signatures of other SAW tags responding to an interrogation signal. A beneficial feature of the present invention is that it can be structured to provide for a xe2x80x9chierarchicalxe2x80x9d control operating system that can be used to determine the correct responses of SAW tags in collision based on all the multiple factors used to determine signal responses.
In one embodiment the system provides for using signal processing techniques that consist of developing a synthetic coded response from the responses of the SAW tag to be identified and generating identification possibilities from such synthetic response. In another embodiment the system only identifies coded responses based on a a particular hierarchical tag level. In still another embodiment, the system signal processing techniques comprise examining at least one known tag anomaly.
A particularly useful embodiment that can be adapted to the environment where the SAW tags will be employed utilizes signal processing techniques comprised of analyzing at least one tag environmental factor. An aspect of this embodiment provides for the environmental factor is selected from the group consisting of: temperature drift; frequency drift; SAW tag position; SAW tag orientation; SAW tag motion; and SAW tag direction of travel.
In yet still another embodiment the system is further comprised of a sensor subsystem that detects other physical properties of the tags, the coded response analyzing subsystem employing the signal processing techniques and the physical properties to generate the possibilities. The present invention also provides for a method of operating the foregoing system and the various embodiment of such system. In another embodiment of the invention the system is further comprised of an inertial guidance system. As aspect of this embodiment provides for the inertial guidance system to be selected from the group consisting of: an inertial guided antenna system; an inertial guided reader system; and an inertial guided platform system.
The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention.
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