Patent ID: 8164422

Claim:
A radio-frequency tag communication system including a plurality of radio-frequency tag communication devices each configured to transmit a transmitted signal toward a radio-frequency tag and to receive a reply signal transmitted from the radio-frequency tag in response to the transmitted signal, thereby effecting radio communication with the radio-frequency tag, said radio-frequency tag communication system comprising: a positional-relationship determining portion configured to determine relative positions of said plurality of radio-frequency tag communication devices by: commanding each of the plurality of radio-frequency tag communication devices to transmit a current transmitted signal within its area of communication, assigning group information indicative of a first group to a first radio-frequency tag communication device from among the plurality of radio-frequency tag communication devices and group information indicative of a second group to a second radio-frequency tag communication device from among the plurality of radio-frequency tag communication devices when the first radio-frequency tag communication device does not receive a reply signal from a first radio-frequency tag in response to its current transmitted signal and the second radio-frequency tag communication device does receive the reply signal from the first radio-frequency tag in response to its current transmitted signal, determining that the first group is adjacent to the second group when both the first radio-frequency tag communication device and the second radio-frequency tag communication device were previously assigned group information indicative of a third group after receiving a previously transmitted signal from a second radio-frequency tag; and a transmission control portion configured to control transmission of said transmitted signal from each of the plurality of radio-frequency tag communication devices, according to a result of determination of said relative positions by said positional-relationship determining portion.