Communications: electrical – Selective – Interrogation response
Reexamination Certificate
2000-06-29
2001-07-24
Zimmerman, Brian (Department: 2635)
Communications: electrical
Selective
Interrogation response
C340S010100, C340S010300, C340S010310, C340S005610, C340S010420, C714S797000, C714S799000
Reexamination Certificate
active
06265962
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electronic identification devices and systems, and in particular, to devices where their application in a system will allow more than one device to be present in the interrogator field at any moment in time. Furthermore, the system requires that all the devices in the field are properly identified by the interrogator.
BACKGROUND OF THE INVENTION
There are methods currently in use that provide varying degrees of success in resolving the collision of the tags, and especially in tags with read/write capability, where communications to the tags is facilitated by an on-board interrogator in the RFID tag. In such a tag, the interrogator can send signals to allow tags to respond with a random number that is manipulated by the interrogator and transmitted to all tags in the field. Only the tag that matches the computed number generated by the interrogator will transmit its data. This process continues until all tags have transmitted their data. This method significantly increases the complexity of the transponder by requiring the transponder to include an interrogator and being only partially effective for regulation of collisions.
Another method of collision resolution is to cause tags to transmit at different frequencies, thereby avoiding a collision of signals. This method significantly increases the complexity of the interrogator while being only partially effective for resolution of the collision.
Yet another method involves the use of spread spectrum techniques. The technique can be either direct sequence spread spectrum (DSSS) or frequency hopping. Either method requires correlation of the signal in the interrogator and requires a very complex interrogator system.
Another method of collision resolution uses part of the unique identification code of the transponder to provide a specific time whereby the transponder transmits its data, and all other times, the transponder remains inactive. This feature is limited by the vast number of unique transmission slots available, and the time required to read all the possible tags in the field. Moreover, a single transponder in the field could take an inordinate amount of time to be read. If the unique identification code is truncated to allow for faster performance, then the probability of an un-resolvable collision occurs due to the duplication of codes.
One other method for resolution is the utilization of a random oscillator and a binary counter on each transponder which enables transmission from the transponder when the counter is in a specific state. All other times the transponder is inactive. This method has the disadvantage of requiring alignment of all the transponders asynchronously before coherent data can be received by the interrogator.
All the above methods require either the use of expensive and complicated interrogator systems, a read-write tag, or they are excessively slow to resolve a useful number of tags.
SUMMARY OF THE INVENTION
The present invention addresses the limitations of the above solutions to the collision problem by providing a simple system for collision resolution that does not require the transponder to have read-write capability nor does the solution require additional complexity to the interrogator to perform the anti-collision function.
The invention comprises a method for sending data from a transponder having at least one memory, a transmission criteria, a transmit state and a full cycle flag. The method comprises the steps wherein the transponder: detects the interrogator, such as by receiving a carrier signal from the interrogator; determines that it is time to transmit the data by verifying that it is the transmit-armed state and that the carrier signal has been modified in a predetermined manner; transmits its data in groups of one or more data bits; determines whether its complete data has been read by the interrogator during the transmission of its data; and sets a full cycle flag after sending its complete data transmission. The transponder determines that the interrogator has read the complete data transmission by verifying that the carrier signal has not been modified until the full cycle flag is set. If the transponder determines that the interrogator did not read the complete data transmission, then the transponder stores a number in memory, iteratively changes the number until the number stored in memory satisfies the transmission criteria, and then transmits its data. This process of transmitting and determining whether the complete data has been read by the interrogator during data transmission is repeated until the transponder determines that the interrogator has read the complete data transmission.
The invention also comprises a method for an interrogator to read one or more RFID transponders in a field by: providing a carrier signal; detecting the presence of at least one transponder; modifying the carrier signal in a predetermined manner, such as by sending out a continuous carrier signal; receiving data from all active transponders in the field; determining whether it has received a valid data transmission by checking the validity of each group of data as it is received; and upon determining an invalid data transmission, modifying the carrier signal—such as by suppressing the signal for a predetermined number of clock cycles—to inform all active transponders in the field that there was an incomplete read. The step of modifying the carrier signal is performed prior to the transponder sending its complete data transmission and it is performed substantially simultaneously upon the determination that invalid data transmission has been received. The interrogator iteratively repeats the steps of receiving data and determining whether it has received valid data, until the interrogator determines that it has read the complete data for each transponder in the field. The step of determining that the interrogator has received an invalid data transmission comprises detecting the interrogator's inability to compute a proper synchronization word, a proper CRC, or a proper word length. After determining that the interrogator has received complete data transmission by determining that the CRC is valid, the carrier signal is modified in a predetermined manner, such as by suppressing the signal for a predetermined number of clock cycles. The complete data for each transponder is transmitted from the interrogator to a computer system for processing.
REFERENCES:
patent: 5339073 (1994-08-01), Dodd et al.
patent: 5583819 (1996-12-01), Roesner et al.
patent: 5742618 (1998-04-01), Lowe
patent: 5745049 (1998-04-01), Akiyama et al.
patent: 5751570 (1998-05-01), Stobbe et al.
patent: 5802080 (1998-09-01), Westby
patent: 5986570 (1999-11-01), Black
patent: 6091319 (1999-11-01), Black
patent: 0 405 695 (1991-01-01), None
patent: 0 689 151 (1995-12-01), None
patent: 0 685 825 (1995-12-01), None
patent: 0 702 324 (1996-03-01), None
patent: 0 709 803 (1996-05-01), None
patent: 0 755 026 (1997-01-01), None
Black Donald L.
Yones Dale
Dalencourt Yves
Micro)n Technology, Inc.
Wells, St. John, Roberts Gregory & Matkin P.S.
Zimmerman Brian
LandOfFree
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