| 摘要 |
<p>An ultrasonic communication system capable of wireless installation and supervised operation is achieved by communicating each information bit as two distinct ultrasonic frequencies separated in frequency enough to assure that the signal strength of neither will be in a deep null at the receiver at the same time. The transmissions can be frequency coded and/ or time coded with a format that recognizes the correct data transmission even if reception of one frequency is lost. By use of transponders and other auxilliary units with periodic polling, supervised operation throughout a building can be maintained with events such as intrusion, fire or emergency as well as failures of particular units of the system reported.</p> |
