| 摘要 |
<p>An intrusion detection system comprises a plurality of sensors (2A...2X) and a corresponding plurality of receivers (3A...3X). Each receiver receives, via the associated sensor, radio frequency signals comprising a multiplicity of transmissions at different frequencies within a predetermined frequency spectrum. The receiver detects the radio frequency signals and computes, for each of a plurality of successive time intervals and for each of the transmission frequencies, a measurement of signal amplitude over the time interval; compares such signal amplitude measurement with at least one threshold and, if the amplitude exceeds the threshold for a predetermined time period, generates a potential alarm signal. A processor (4) compares potential alarm signals from a plurality of sensors and determines that an intrusion has occurred if the potential alarm signal for a particular station does not coincide with a potential alarm signal for a neighbouring sensor. Each receiver may output an intruder alarm signal when potential alarm signals occur simultaneously for more than a preset number of a multiplicity of the transmission frequencies.</p> |
