Patent ID: 8680966

Claim:
A method for radio frequency identification, comprising: providing a modulated illumination signal configured to illuminate a radio frequency identification (RFID) tag within a zone of interest, the illumination signal including at least a first discrete frequency and a second discrete frequency disposed within a first range of frequencies and modulated to represent a sequence of bits each having a first bit state or a second, opposite bit state; receiving the illumination signal at the RFID tag; rectifying the illumination signal at the RFID tag to generate a wake signal; applying the wake signal to a processor associated with the RFID tag; waking the processor in response to the wake signal and subsequently powering the processor from a battery coupled to the processor; sampling the received illumination signal; dynamically adjusting in the processor a noise amplitude floor value associated with each of the discrete frequencies of the sampled illumination signal; determining in the processor a threshold amplitude value above the noise amplitude floor value above which each of the discrete frequencies of the sampled illumination signal is deemed to represent a bit and below which each of the discrete frequencies of the sampled illumination signal is deemed to not represent a bit; correlating the sampled illumination signal to determine its bit sequence; correlating the bit sequence of the sampled illumination signal against a predetermined key comprising a plurality of bits to determine if the sampled illumination signal is sufficiently correlated with the predetermined key; transmitting an identification signal from the RFID tag in response to determining that the received illumination signal is sufficiently correlated with the predetermined key, the identification signal modulated to reflect an access code value associated with the RFID tag, and the identification signal disposed within a second range of frequencies outside the first range of frequencies; receiving the identification signal; demodulating the received identification signal to obtain the access code value; and checking the access code value against a database of authorized RFID tag access code values; and taking a first action in response to determining that the RFID tag access code value is authorized.