| 摘要 |
PROBLEM TO BE SOLVED: To sense the transfer of a signal in a bidirectional communication, and to prevent unlocking caused by the false transfer of a signal in the certifying process for unlocking an automobile. SOLUTION: In a sensing method for a transfer or wiretapping in bidirectional non-contact data transmission, an amplitude attenuation (A1) generated in out-going data transmission is compared with an amplitude attenuation (A2) generated in its returne transmission. The amplitude attenuation (A1) generated in outgoing route is coded together with its answering signal. When the magnitudes of the attenuation determined by the comparison are equal to each other, the possibility of a transfer process can be excluded. In order to increase further the certainty of this system, a carrier frequency (F2) of a request signal is also compared with a carrier frequency (F21) of the answering signal. An ID code can be also incorporated in the signals. |
