| CPC B60R 25/24 (2013.01) | 7 Claims |
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1. An authentication system comprising:
a first communication device including:
a first transmitting part configured to communicate in a first frequency band; and
a first transmitting-and-receiving part configured to communicate in a second frequency band; and
a second communication device including:
a first receiving part configured to communicate in the first frequency band; and
a second transmitting-and-receiving part configured to communicate in the second frequency band,
wherein the first communication device transmits a command in the first frequency band from the first transmitting part, and
wherein, upon receipt of the command by the first receiving part, the second communication device activates the second transmitting-and-receiving part, generates an authentication key for a response signal, and transmits the response signal including the generated authentication key in the second frequency band, from the second communication device,
wherein the first communication device has a plurality of said first transmitting parts, and, following the transmission of the command from any one of the plurality of first transmitting parts, transmits a plurality of signal strength measurement signals in the first frequency band, sequentially, from the plurality of first transmitting parts,
wherein the second communication device acquires signal intensities upon receipt of the plurality of signal strength measurement signals by the first receiving part,
wherein, upon determining that the authentication key included in the response signal received from the second communication device is valid, the first communication device transmits a distance measurement request signal from the first transmitting-and-receiving part, in the second frequency band, the distance measurement request signal requesting transmission of a distance measurement signal including an ID of the second communication device,
wherein, upon receipt of the distance measurement request signal including the ID of the second communication device, the second communication device transmits the distance measurement signal in the second frequency band from the second transmitting-and-receiving part,
wherein the first communication device calculates a distance to the second communication device based on the distance measurement request signal and the distance measurement signal, and determines, based on the calculated distance, whether a transmission source of the distance measurement signal is the second communication device that is authorized or an unauthorized relay device,
wherein the first communication device has a second receiving part configured to communicate in a third frequency band,
wherein the second communication device has a second transmitting part configured to communicate in the third frequency band,
wherein, following the transmission of the distance measurement signal from the second transmitting-and-receiving part, the second communication device transmits a position determination signal in the third frequency band from the second transmitting part,
wherein the position determination signal represents relative positions between the plurality of first transmitting parts and the second communication device, based on receiving intensities of the plurality of signal strength measurement signals, transmitted from the plurality of first transmitting parts, at the first receiving part,
wherein, upon receipt of the position determination signal by the second receiving part, the first communication device determines a position of the second communication device based on the relative positions between the plurality of first transmitting parts and the second communication device, represented by the position determination signal, and
wherein, following the transmission of the distance measurement signal, and prior to the transmission of the position determination signal, the second communication device reduces supply of power to the second transmitting-and-receiving part for a predetermined period of time.
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