發送短信 : A narrowband ultrasonic ranging method for multiple moving sensor nodes

 _    _    _    _     ______    _____             
| \  / || | || | ||  /_____//  |  ___||   ____    
|  \/  || | || | ||  `____ `   | ||__    |    \\  
| .  . || | \\_/ ||  /___//    | ||__    | [] ||  
|_|\/|_||  \____//   `__ `     |_____||  |  __//  
`-`  `-`    `---`    /_//      `-----`   |_|`-`   
                     `-`                 `-`