PURPOSE: A collision prevention method between tags is provided to effectively prevent a collision by using a rate between a collision slot and an idle slot. CONSTITUTION: An RFID(radio frequency identification) reader(101) transmits the identification frequency of a round frame in a point of a time slot in order to reduce the recognition time of multiple tags(102). The slot includes a higher rate between the rate of a collision slot and the rate of an idle slot in response to data transmitted from the multiple tags. When the rate of the idle slot is over a predetermined rate in the response data transmitted from the multiple tags, slot counts of a next round frame are reduced as predetermined numbers. [Reference numerals] (101) RFID reader; (AA) Identification frequency (1); (BB) Response data; (CC) Identification frequency (2); (DD) Tag (T1); (EE) Tag (T2); (FF) Tag (T3)
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