Patent ID: 8035488

Claim:
An information access system for accessing information stored in a contactless information storage device, comprising: a reader/writer device connected to an information processing apparatus, and being adapted to continually transmit an ID request signal at a first frequency in transmission time periods in a transmission cycle and to be continuously ready to receive an RF signal at a second frequency which is different from the first frequency; and an active-type contactless information storage device having: a memory, a control unit, a battery, a timer for measuring time, a receiver unit for sensing, using power supplied from the battery, a carrier of an RF signal at the first frequency for detection, and a transmitter unit for transmitting, using power supplied from the battery, a response signal at the second frequency when the ID request signal is received, wherein the control unit controls, in carrier sensing periods occurring in a carrier sensing cycle, the transmitter unit to be in an inactive state and the receiver unit to be in an active state and sense, using power supplied from the battery, a carrier of an RF signal at the first frequency, the carrier sensing period being shorter than the transmission time period of the ID request signal, the carrier sensing cycle being longer than the transmission cycle of the ID request signal, the carrier sensing cycle being determined according to the timer, when the receiver unit senses and detects a carrier of an RF signal at the first frequency in one of the carrier sensing periods, the control unit causes the receiver unit to receive, using power supplied from the battery, the ID request signal before a subsequent one of the carrier sensing periods, and, in response to the ID request signal, causes the transmitter unit to transmit, using power supplied from the battery, a response signal at the second frequency carrying an ID of the active-type contactless information storage device stored in the memory before the subsequent carrier sensing period; and when the receiver unit detects no carrier in one of the carrier sensing periods, the control unit controls the receiver unit and the transmitter unit to be in the inactive state during a non-carrier-sensing period between the one carrier sensing period and a subsequent one of the carrier sensing periods.