Method for resolving signal collisions between multiple RFID transponders in a field
DCFirst Claim
1. A method for an interrogator reading one or more RFID transponders in a field comprising the steps of:
- a. providing a carrier signal;
b. detecting the presence of at least one transponder;
c. receiving data from all active transponders in the field;
d. determining whether the interrogator has received a valid data transmission; and
e. upon determining an invalid data transmission, informing all active transponders in the field that there was an incomplete read, the informing including suppressing the carrier.
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Reexamination
Accused Products
Abstract
Communications between an RFID interrogator and an RFID transponder require that no more than one transponder be present in the reading range of the interrogator and transmitting into motion at any given time. If multiple transponders are in the field, then a collision between the return signals of the transponders occurs, rendering the signals unreadable. A method to resolve the collisions and allow for accurate transmission of each transponder'"'"'s data is given. This method is especially effective over other methods when the transponder is a read-only type of device, whereby there is no communications interrogator on board the read-only transponder.
260 Citations
23 Claims
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1. A method for an interrogator reading one or more RFID transponders in a field comprising the steps of:
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a. providing a carrier signal; b. detecting the presence of at least one transponder; c. receiving data from all active transponders in the field; d. determining whether the interrogator has received a valid data transmission; and e. upon determining an invalid data transmission, informing all active transponders in the field that there was an incomplete read, the informing including suppressing the carrier. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method for an interrogator reading one or more RFID transponders in a field, the interrogator including a demodulator, the method comprising:
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providing a carrier signal; detecting the presence of at least one transponder, the detecting including receiving data from the demodulator and modifying the carrier signal by suppressing the carrier signal for a predetermined number of clock cycles; receiving data from all active transponders in the field, the receiving including receiving the data in groups of one or more bits and checking the validity of each group of data as the group is received; determining whether the interrogator has received a valid data transmission by detecting the interrogator'"'"'s inability to compute a proper synchronization word, a proper CRC, or a proper word length; upon determining an invalid data transmission, modifying the carrier signal to inform all active transponders in the field that there was an incomplete read; and transmitting the complete data for each transponder from the interrogator to a computer system for processing. - View Dependent Claims (14, 15, 16, 17)
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18. A method for an interrogator reading one or more RFID transponders in a field, the interrogator including a demodulator, the method comprising:
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providing a carrier signal; detecting the presence of at least one transponder, the detecting including receiving data from the demodulator and modifying the carrier signal in a predetermined manner; receiving data from all active transponders in the field, the receiving including receiving the data in groups of one or more bits and checking the validity of each group of data as it is received; determining whether the interrogator has received a valid data transmission;
the receiving and the determining being iteratively repeated until the interrogator determines that the interrogator has read complete data for each transponder in the field, the determining that the interrogator has read complete data for one of the transponders including determining that the CRC is valid and suppressing the carrier;upon determining an invalid data transmission, modifying the carrier signal to inform all active transponders in the field that there was an incomplete read; and transmitting the complete data for each transponder from the interrogator to a computer system for processing. - View Dependent Claims (19, 20, 21, 22, 23)
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Specification