Patent ID: 7994899

Claim:
An information access system for accessing information in a contactless information storage device, comprising: an active-type contactless information storage device having a memory, a timer for measuring time, a first control unit, a first receiver unit for sensing a carrier of an RF signal at a first frequency for detection, and a first transmitter unit for transmitting a response signal at a second frequency different from the first frequency in response to reception of an information request signal; a first reader/writer device connected to an information processing apparatus, and having a second control unit, a second transmitter unit for cyclically transmitting an information request signal at the first frequency in a first transmission period and going into an inactive state in a second transmission period, under the control of the second control unit, and a second receiver unit adapted to be continuously ready to receive an RF signal at the second frequency; and a second reader/writer device connected to the information processing apparatus, and having a third control unit, a third transmitter unit for cyclically transmitting an information request signal at the first frequency in the second transmission period and going into an inactive state in the first transmission period, under the control of the third control unit, and a third receiver unit adapted to be continuously ready to receive an RF signal at the second frequency, wherein the first control unit controls, in carrier sensing periods occurring in a carrier sensing cycle, the first transmitter unit to be in an inactive state and the first receiver unit to be in an active state and sense a carrier of an RF signal at the first frequency, the carrier sensing cycle being shorter than each of the first and second transmission periods, the carrier sensing cycle being determined according to the timer, causes the first receiver unit to further receive the information request signal when the first receiver unit detects a carrier of an RF signal at the first frequency in any one of the carrier sensing periods, and further causes the first transmitter unit to transmit a response signal at the second frequency that carries a piece of information stored in the memory in response to the information request signal, and controls the active-type contactless information storage device to go into a sleep mode of operation during a non-carrier-sensing period between one of the carrier sensing periods and a subsequent one of the carrier sensing periods so that the first receiver unit and the first transmitter unit are in the inactive state, when the first receiver unit detects no carrier in the one carrier sensing period.