Patent ID: 8193910

Claim:
An interrogator that makes wireless communication with a plurality of transponders, comprising: a temporary number specify section transmitting to the plurality of transponders a request for transmission of an ON signal, the temporary number specify section receiving the ON signal from a transponder among the plurality of transponders in response to the request for transmission of an ON signal, the ON signal indicating a unit bit string having a predetermined length in a bit string of a temporary number generated by the transponder, the ON signal being transmitted within a time slot corresponding to the unit bit string, the temporary number specify section specifying a portion of the bit string of the temporary number based on the ON signal, the temporary number specify section repeating specifying the portion of the bit string of the temporary number based on preset priority order of plural kinds of unit bit strings until the entire bit string of the temporary number is specified; and an identification information obtaining section transmitting, when the entire bit string of the temporary number is specified, a request for transmission of identification information to the transponder, the identification information obtaining section receiving the identification information transmitted from the transponder in response to the request for transmission of the identification information, wherein when the temporary number specify section receives a plurality of ON signals respectively transmitted from the plurality of transponders in response to the request for transmission of the ON signal, the interrogator selects the most prioritized unit bit string from among the plural kinds of unit bit strings respectively indicated by the plurality of ON signals based on the preset priority order and transmits a multi-reception acknowledgement including the selected unit bit string to the plurality of the transponders, when the multi-reception acknowledgement is received by the transponder and the unit bit string indicated by the transmitted ON signal is different from the selected unit bit string, the multi-reception acknowledgement causes the transponder to increase a standby time to a transmission of a next ON signal to the interrogator, and when the multi-reception acknowledgement is received by the transponder, when the unit bit string indicated by the transmitted ON signal is the selected unit bit string, and when the standby time is zero, the multi-reception acknowledgement causes the transponder to transmit the next ON signal to the interrogator.