Patent ID: 7536152

Claim:
An information access system for accessing information stored in a contactless information storage device, said information access system comprising: an active contactless information storage device having a memory, a first control unit, a battery, a timer for measuring time, a receiver unit for sensing carriers of RF signals at first and second different frequencies for detection, and a transmitter unit for transmitting a response signal at a third or fourth frequency different from said first and second frequencies in response to reception of an ID 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 ID request signal at said first frequency under the control of said second control unit, and a second receiver unit adapted to be continuously ready to receive an RF signal at said third frequency, and a second reader/writer device connected to an information processing apparatus, and having a third control unit, a third transmitter unit for cyclically transmitting an ID request signal at said second frequency under the control of said third control unit, and a third receiver unit adapted to be continuously ready to receive an RF signal at said fourth frequency, wherein said first control unit controls said first receiver unit to sense a carrier of an RF signal at said first frequency in first predetermined periods occurring in a predetermined cycle and sense a carrier of an RF signal at said second frequency in second predetermined periods occurring in said predetermined cycle, when said first receiver unit senses and detects a carrier of an RF signal at one of said first and second frequencies in a particular predetermined period, said first control unit causes said first receiver unit to receive further the ID request signal, and, in response to the ID request signal, causes said first transmitter unit to transmit a response signal at a corresponding one of said third and fourth frequencies that carries an ID of said active contactless information storage device stored in said memory; in the carrier sensing, said first control unit causes said first receiver unit to be in an active state and said transmitter unit to be in an inactive state in the first and second predetermined periods; and when said first receiver unit attempts to sense a carrier of an RF signal at said first frequency in the first predetermined period but detects no carrier, said first control unit controls said first receiver unit and said first transmitter unit to maintain the inactive state during a non-carrier sensing period between the first predetermined period for carrier sensing and the second predetermined period for subsequent carrier sensing.