| 摘要 |
An ultrasonic receiver receives an ultrasonic signal having a period in which an amplitude thereof progressively increases as time elapses. A pattern matching unit determines whether a comparative pattern, which is generated as a result of comparison between the respective maximum amplitude values of a plurality of successive waves of said wave signal and a threshold value set by a threshold setting unit, matches a reference pattern or not during the period of the ultrasonic signal. The pattern matching unit determines that the ultrasonic receiver has successfully received the ultrasonic signal if the comparative pattern matches the reference pattern.
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