Method and system for communicating with and tracking RFID transponders
First Claim
1. An RFID system comprising:
- (A) a plurality of RFID transponders, each of said plurality of RFID transponders having a unique identification code, for receiving a signal and for generating a response signal based thereon, each of said RFID transponders having a random number generator used for determining whether to respond to a received message addressed to all of said plurality of RFID transponders;
(B) a host computer for generating a message for transmission to at least one of said RFID transponders; and
(C) at least one interrogator connected to said host computer having an interrogator transmitter and an interrogator receiver which operate in half-duplex mode, wherein said interrogator transmitter transmits messages received from said host computer to said plurality of RFID transponders during a first part of said half-duplex mode and which provides an illumination signal to said plurality of RFID transponders during a second part of said half-duplex mode and said interrogator receiver receives signals reflected by said at least one RFID transponders and provides said received signals to said host computer;
wherein said host computer identifies each of said unique identification codes associated with each of said plurality of RFID transponders by iteratively transmitting a message including a variable having a predetermined initial value to each of said RFID transponders, and only said RFID transponders which generate a random number greater than said variable respond to said message by transmitting identification codes associated with said respective RFID transponders.
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Accused Products
Abstract
An RFID system and method for communicating between a host computer, one or more interrogators connected to the host computer, and a large body of transponders distributed within an area covered by the interrogators. Each transponder originally has a common identification code, and upon initialization by the host computer internally generates a unique identification code based upon an internally generated random number. The host, through the interrogators, reads each of the identification codes associated with each transponder by iteratively transmitting a read identification code command along with a controlled variable. Each transponder compares the received controlled variable to an internally generated random number, and selectively transmits its identification code based upon the outcome of this comparison. After the completion of each read identification code iteration, the host adjusts the controlled variable based upon the responses received in the previous iteration. Preferably, communications between the interrogators and the transponders are DSSS signals in TDMA format, and the transponders use the random number generator to assign a time slot for transmission of their response. Each interrogator includes an antenna system utilizing a switch matrix to connect multiple antennas having different polarizations, which ensures that all transponders within the range of the interrogator receive the signals from the interrogator. In a further aspect, the interrogators are arranged in groups, each group in nearest neighbor format, to reduce the time for reading the transponders and the emissions generated when more than one interrogator is active at the same time.
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Citations
38 Claims
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1. An RFID system comprising:
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(A) a plurality of RFID transponders, each of said plurality of RFID transponders having a unique identification code, for receiving a signal and for generating a response signal based thereon, each of said RFID transponders having a random number generator used for determining whether to respond to a received message addressed to all of said plurality of RFID transponders;
(B) a host computer for generating a message for transmission to at least one of said RFID transponders; and
(C) at least one interrogator connected to said host computer having an interrogator transmitter and an interrogator receiver which operate in half-duplex mode, wherein said interrogator transmitter transmits messages received from said host computer to said plurality of RFID transponders during a first part of said half-duplex mode and which provides an illumination signal to said plurality of RFID transponders during a second part of said half-duplex mode and said interrogator receiver receives signals reflected by said at least one RFID transponders and provides said received signals to said host computer;
wherein said host computer identifies each of said unique identification codes associated with each of said plurality of RFID transponders by iteratively transmitting a message including a variable having a predetermined initial value to each of said RFID transponders, and only said RFID transponders which generate a random number greater than said variable respond to said message by transmitting identification codes associated with said respective RFID transponders. - View Dependent Claims (2, 3, 4, 5, 6, 35)
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7. A method for a host to read an identification code from a plurality of RFID transponders each having unique identification codes, comprising the steps of:
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(A) iteratively transmitting a read identification code command and a variable having a predetermined initial value from said host to said plurality of RFID transponders;
(B) receiving, at each of said plurality of RFID transponders, said read identification code command and said variable;
(C) generating, at each of said plurality of RFID transponders, a random number upon receipt of said read identification code and said variable;
(D) comparing, at each of said plurality of RFID transponders, said variable with said generated random number;
(E) transmitting, by each of said RFID transponders where said generated random number is greater than said variable, an identification code associated with each RFID transponder and then becoming inactive such that each RFID transponder does not respond to further read identification code commands during a current read identification code command iteration;
(F) waiting, by each of said RFID transponders where said generated random number is not greater than said variable, for a next transmission of said read identification code command and said variable;
(G) intelligently adjusting, by said host, the value of said variable for the next transmission of said read identification code command and said variable; and
(H) examining said variable at said host and ceasing the iterative transmission of said read identification code command when no RFID transponders respond by transmitting their identification code in response to a final value of said variable. - View Dependent Claims (8)
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9. A method for re-selecting an identification code for each of a plurality of RFID transponders, comprising the steps of:
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(A) transmitting a re-select identification code command to each of a plurality of RFID transponders;
(B) generating, at each of said plurality of RFID transponders, a first random number and calculating a new identification code based upon said random number;
(C) iteratively transmitting a read identification code command and a variable having a predetermined initial value from said host to said plurality of RFID transponders;
(D) receiving, at each of said plurality of RFID transponders, said read identification code command and said variable;
(E) generating, at each of said plurality of RFID transponders, a random number upon receipt of said read identification command and said variable;
(F) comparing, at each of said plurality of RFID transponders, said variable with said generated random number;
(G) transmitting, by each of said RFID transponders where said generated random number is greater than said variable, an identification code associated with each RFID transponder and then becoming inactive such that each RFID transponder does not respond to further read identification code commands during a current read identification code command iteration;
(H) waiting, by each of said RFID transponders where said generated random number is not greater than said variable, for a next transmission of said read identification code command and said variable;
(I) intelligently adjusting, by said host, the value of said variable for the next transmission of said read identification code command and said variable; and
(J) examining said variable at said host and ceasing the iterative transmission of said read identification code command when no RFID transponders respond by transmitting their identification code in response to a final value of said variable. - View Dependent Claims (10)
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11. An interrogator for communicating with an RFID transponder in an RFID system which is connected to a host computer, comprising:
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(A) at least one antenna;
(B) a transmitter connected to said at least one antenna for transmitting an FSK modulated spread spectrum signal on said at least one antenna during a transmitting mode and a BPSK modulated spread spectrum signal during a receiving mode;
(C) a receiver connected to said at least one antenna for receiving a spread spectrum signal in PSK format, and (D) a controller connected to said transmitter and said receiver for controlling said transmitter and said receiver and communicating with a host computer. - View Dependent Claims (12, 13, 14, 15, 16, 17, 19, 38)
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18. An antenna assembly for an RFID interrogator comprising:
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(A) a first antenna having a first polarization;
(B) a second antenna having a second polarization which is orthogonal to said first polarization; and
(C) an antenna switch network connected to said first and second antennas for selectively selecting one of said first and said second antennas for connection to a transmitter.
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20. A transponder for communicating with an interrogator in an RFID system, comprising:
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(A) a first antenna element having a first predetermined dimensional configuration;
(B) a second antenna element having a second predetermined dimensional configuration;
(C) an impedance modulator connected between said first antenna element and said second antenna element which causes said first antenna element to be electrically connected to said second element in a first state and to be electrically isolated from said second element in a second state;
(D) a receiver for receiving a message within an FSK modulated spread spectrum signal connected to said first antenna element, said second antenna element and said impedance modulator; and
(E) a controller connected to said receiver which receives said message and selectively responds to said message in PSK format by reflecting an illumination signal transmitted by said interrogator by selectively switching said impedance modulator between said first state and said second state. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27)
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28. A method of generating a random number in an RFID transponder, comprising the steps of:
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(A) calculating a random seed based upon the difference between a local clock signal and a clock signal derived from either a received signal or random noise;
(B) supplying said random seed to a random number generator; and
(C) generating a random number based upon said random seed.
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29. An apparatus for generating a random number, comprising:
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(A) a first clock input derived from a local clock oscillator;
(B) a second clock input derived from a received signal or random noise;
(C) means connected to said first clock input and said second clock input for generating a random number based upon the timing difference between said first clock input and said second clock input.
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30. A method for controlling a plurality of groups of interrogators in an RFID system, comprising the steps of:
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arranging each interrogator within a group of interrogators in nearest neighbor format having a predetermined order; and
activating only corresponding interrogators within each group of interrogators for transmission of signals to at least one RFID transponder within a zone covered by said respective activated interrogators.
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31. A method for generating a unique identification code for each of a plurality of RFID transponders originally having a common default identification code, comprising the steps of:
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(A) transmitting a re-select identification code command to each of a plurality of RFID transponders;
(B) generating, at each of said plurality of RFID transponders, a first random number and calculating a new identification code based upon said random number;
(C) iteratively transmitting a read identification code command and a variable having a predetermined initial value from said host to said plurality of RFID transponders;
(D) receiving, at each of said plurality of RFID transponders, said read identification code command and said variable;
(E) generating, at each of said plurality of RFID transponders, a random number upon receipt of said read identification code and said variable;
(F) comparing, at each of said plurality of RFID transponders, said variable with said generated random number;
(G) transmitting, by each of said RFID transponders where said generated random number is greater than said variable, an identification code associated with each RFID transponder and then becoming inactive such that each RFID transponder does not respond to further read identification code commands during a current read identification code command iteration;
(H) waiting, by each of said RFID transponders where said generated random number is not greater than said variable, for a next transmission of said read identification code command and said variable;
(I) intelligently adjusting, by said host, the value of said variable for the next transmission of said read identification code command and said variable; and
(J) examining said variable at said host and ceasing the iterative transmission of said read identification code command when no RFID transponders respond by transmitting their identification code in response to a final value of said variable. - View Dependent Claims (32)
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33. A method for a host having a plurality of transmitting antennas to read an identification code from a plurality of RFID transponders each having unique identification codes, comprising the steps of:
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(A) iteratively transmitting a read identification code command and a variable having a predetermined initial value from said host to said plurality of RFID transponders on each of said plurality of transmitters;
(B) receiving, at each of said plurality of RFID transponders, said read identification code command and said variable;
(C) generating, at each of said plurality of RFID transponders, a random number upon receipt of said read identification code and said variable;
(D) comparing, at each of said plurality of RFID transponders, said variable with said generated random number;
(E) transmitting, by each of said RFID transponders where said generated random number is greater than said variable, an identification code associated with each RFID transponder and then becoming inactive such that each RFID transponder does not respond to further read identification code commands during a current read identification code command iteration;
(F) waiting, by each of said RFID transponders where said generated random number is not greater than said variable, for a next transmission of said read identification code command and said variable;
(G) receiving at said host said transmitted identification codes associated with particular RFID transponders and storing said identification codes and associated antenna information in memory so that further communication with a particular one of said plurality of transponders is performed by using said identification code and said antennal information;
(H) intelligently adjusting, by said host, the value of said variable for the next transmission of said read identification code command and said variable; and
(I) examining said variable at said host and ceasing the iterative transmission of said read identification code command when no RFID transponders respond by transmitting their identification code in response to a final value of said variable. - View Dependent Claims (36)
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34. An RFID system for tracking election ballots comprising:
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(A) a plurality of RFID transponders, each of said plurality of RFID transponders having a unique identification code and connected to a separate ballot, for receiving a signal and for generating a response signal based thereon, each of said RFID transponders having a random number generator used for determining whether to respond to a received message addressed to all of said plurality of RFID transponders and a memory for storing election data;
(B) a host computer for generating a message for transmission to at least one of said RFID transponders and for controlling the storage of election data within each of said ballots; and
(C) at least one interrogator connected to said host computer having an interrogator transmitter and an interrogator receiver which operate in half-duplex mode, wherein said interrogator transmitter transmits messages received from said host computer to said plurality of RFID transponders during a first part of said half-duplex mode and which provides an illumination signal to said plurality of RFID transponders during a second part of said half-duplex mode and said interrogator receiver receives signals reflected by said at least one RFID transponders and provides said received signals to said host computer;
wherein said host computer identifies each of said unique identification codes associated with each of said plurality of RFID transponders by iteratively transmitting a message including a variable having a predetermined initial value to each of said RFID transponders, and only said RFID transponders which generate a random number greater than said variable respond to said message by transmitting identification codes associated with said respective RFID transponders.
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37. In a communications system having a first device having a transmitter and a receiver and a plurality of second devices, each of said second devices having a transmitter and a receiver, where communications between said first device and said plurality of second devices is in TDMA format having a plurality of time slots for transmission, a method for determining if more than one second device has transmitted a signal to said first device at the same time during a current TDMA communications period, comprising the steps of:
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(A) sampling the relative power in an analog baseband channel of said receiver in said first device during each of said time slots;
(B) sampling the relative power in an analog baseband channel of said receiver in said first device during a period of no communications;
(C) comparing said sampled relative power in each of said time slots to said sampled relative power in said period of no communications;
(D) setting, if said comparison for a particular one of said time slots produces a value of greater than unity by a predetermined amount, said particular time slot to be occupied;
(E) determining which of said time slots did not have an accepted message;
(F) comparing said time slots which did not have an accepted message to said occupied time slots;
(G) determining that each of said time slots which did not have an accepted message and which is occupied represents a time slot in which more than one second device transmitted a message at the same time.
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Specification