| 摘要 |
PROBLEM TO BE SOLVED: To establish communication between an in-vehicle authentication device 20 and a mobile unit 40 using an ultrasonic signal, to properly determine a distance between the in-vehicle authentication device 20 and the mobile unit 40.SOLUTION: An in-vehicle authentication device 20 includes a transmitting/receiving unit 24 which transmits/receives an ultrasonic signal. A mobile unit 40 includes a transmitting/receiving unit 42 which transmits/receives the ultrasonic signal. The in-vehicle authentication device 20 transmits the ultrasonic signal by means of the transmitting/receiving unit 24. The mobile unit 40 receives the ultrasonic signal and transmits an ultrasonic signal according thereto. The in-vehicle authentication device 20 receives the ultrasonic signal transmitted from the mobile unit 40, performs electronic authentication in response thereto, and calculates a distance between the in-vehicle authentication device 20 and the mobile unit 40 on the basis of a difference between the time when the ultrasonic signal is received and the time when the ultrasonic signal is transmitted. Predetermined processing is executed based on the authentication, provided that the mobile unit 40 is located within a predetermined range on the basis of the calculated distance. |
