Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-06-27
2002-01-22
Lee, Benjamin C. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S572800, C343S70000R, C343S872000, C342S042000
Reexamination Certificate
active
06340932
ABSTRACT:
FIELD OF THE INVENTION
Embodiments of the present invention relate to communication systems of the type having multiple transmitting and receiving devices that share a common communication medium; and, to methods for establishing communication in the presence of large numbers of such devices.
BACKGROUND OF THE INVENTION
Conventional data communication systems have been applied to accomplish object identification using the medium of radio broadcast. Such radio frequency identification (RFID) systems find application in the fields of materials handling, inventory control, and generally in the field of tracking personnel, objects, and animals. In an exemplary arrangement, such a system may include an interrogator and several thousand transceivers, each transceiver being packaged as a disposable label or tag and placed on an object, animal or person to be tracked. Each transceiver is manufactured using integrated circuit technology, programmed with a unique identifier, and assembled with a printed circuit antenna to form a flat assembly for incorporation into the label or tag. Typically, the interrogator has a fixed location, while transceivers are moved from time to time in and out of the communication field of the interrogator. It is highly desirable to accurately and quickly identify transceivers from a population of transceivers which may number in the billions. At the same time, it is highly desirable to reduce the cost of each transceiver to an absolute minimum.
Accurate and reliable detection of transceivers is made difficult by a number of factors including, for example, (a) transceivers have a limited amount of power available to operate when required to respond with a radio transmission; (b) the orientation of the transceiver antenna may be unsuitable for absorbing sufficient power from the signal transmitted by the interrogator; (c) the orientation of the antenna of the transceiver may be unsuitable for providing a transmitted signal sufficient for accurate reception by the interrogator, (d) cooperation of a transceiver with the interrogator may require sophisticated logic in the transceiver to accurately perform the transceiver's portion of a communication protocol used to obtain an open communication channel between the interrogator and a single transceiver, and (e) transceivers transmitting simultaneously may cause a so-called collision.
There remains a need for a communication system suited for coordinating the use of a common medium among potentially billions of transceivers for interrogation or control activities to be accomplished in a limited time. In addition, there remains a need in some applications to minimize the circuitry, firmware, and software complexity required at each transceiver, to extend the operating range of communication, and to support larger numbers of individual identification numbers perhaps at the expense of complexity at the interrogator. Without these improvements, the size and cost per transceiver cannot be reduced to permit new and improved communication systems that employ inexpensive disposable transceivers such as identification tags, baggage tags, inventory labels, and the like.
SUMMARY OF THE INVENTION
A system in one implementation according to various aspects of the present invention includes a monitor and a plurality of transceivers that communicate over a common medium. The monitor includes a first transmitter, a first receiver, and a processor. Each transceiver includes a resonant circuit, a transmitter, a receiver, and an antenna coupled to the resonant circuit. The processor performs a method for performing transceiver communication that includes the steps of: (a) transmitting from the first transmitter a first frequency for a first duration; (b) after lapse of the first duration, receiving via the first receiver a response signal from at least one of the resonant circuits; (c) determining a second frequency from the received response signal; and (d) performing transceiver communication using the second frequency.
Transceivers of the type having a resonant circuit coupled to an antenna, when operating in close proximity to each other, may interfere with the response from a single transceiver by absorbing the energy intended to be received by the transceiver, absorbing the energy transmitted by the transceiver, or altering the resonant frequency of the resonant circuit. By determining the second frequency for transceiver communication, the monitor may establish communication with the single transceiver at a frequency better suited for transferring operative power to the transceiver, for conducting an interrogation protocol for identifying the transceiver, or for data transfer. Communication is maintained in spite of variation in the resonant frequency of the resonant circuit which may arise from coupling as discussed above or from variation in manufacturing and operating environment (e.g., temperature, humidity, relative movement, or component aging).
The monitor may further include a first antenna coupled to the first transmitter and a squelch circuit for dissipating energy on the antenna after lapse of the first duration and before receiving from the first receiver the response signal from the resonant circuit. By quickly dissipating energy, the response signal may be more quickly and accurately received by the second receiver and consequently the second frequency may be more quickly and accurately determined, increasing system sensitivity and reliability. Obtaining quicker receiving from the second receiver extends the operating range of the monitor or permits operation with weaker signals. Weaker signals may originate from transceivers located further from the monitor or in an orientation that is detrimental to reception by the first receiver. Such detrimental orientation of the antenna in the transceiver may be with respect to the first antenna of the monitor or with respect to other transceivers proximate to the transceiver antenna.
The monitor may further include the second receiver providing phase detection, or a signal analyzer provides phase detection. Phase detection providing phase information regarding the received response signal. The processor may further determine the second frequency in accordance with the phase information. Phase information varies over a wider range of values near a resonant frequency. By determining the second frequency in accordance with phase information, the second frequency may be more accurately determined. Communication with a more accurate second frequency improves the efficiency of transferring operative power to a transceiver, permits faster or more accurate identification of transceivers, extends the operating range of the monitor, overcomes problems of detrimental orientation discussed above, or permits faster or more accurate data transfer between the monitor and a single transceiver.
When each transceiver has a respective identification number comprising a common total number of portions, a method of determining an identification number of a transceiver of a plurality of such transceivers in one embodiment according to various aspects of the present invention includes the steps of: (a) transmitting a start signal; (b) receiving a reply at a time after the start signal; (c) determining a number in accordance with the time determined in step (b); (d) transmitting a start signal and the number determined in step (c); (d) repeating steps (b) through (d) until a count of performances of the step of transmitting is not less than the common total; and (f) determining the identification number in accordance with each reply.
By repeating the steps of transmitting a number of times not less than the common total, a step of detecting whether a collision occurred is not necessary. The reply may convey no more information than the fact that a reply has been made, thereby eliminating the need for a longer duration of reply. By dividing an identification number into portions and applying the protocol discussed above, a large number of unique identification numbers is practical (e.g., 2
Coulthard John J.
Fowler Billy C.
Jaecks Howard K.
Lastinger Roc A.
Picard Paul A.
Bachand William R
Lee Benjamin C.
RF Code, Inc.
Squire Sanders & Dempsey L.L.P.
Whittington Stuart A
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