Perimeter security system

Abstract

A security system for detecting physical intrusion in a monitored area including a plurality of radio units arranged in a network around the monitored area to determine received signal strength and pass variations thereof through the radio units to a base station.

1 . A security system for detecting physical intrusion in a monitored area comprising
 a plurality of radio units arranged in a network, each of said radio units having a signal transmitter, a signal receiver, a circuit coupled with the receiver to measure the signal strength of signals received by the receiver and produce an output representative of received signal strength, a controller responsive to said circuit output to cause said transmitter to transmit a signal representative of the strength of the signal received by said receiver and to provide said radio unit with a receive mode and a transmit mode such that said receiver and said transmitter do not operate simultaneously; and   a base station positioned to receive the transmitted signal from one of said radio units and to provide an indication of intrusion into the monitored area, said radio units being positioned such that each radio is within communication range of at least one other radio.   
   
   
       2 . A security system for detecting physical intrusion in a monitored area as recited in  claim 1  wherein said transmitter signals are frequency hopped. 
   
   
       3 . A security system for detecting physical intrusion in a monitored area as recited in  claim 1  wherein each of said radio units includes a memory coupled with said controller for storing radio unit control algorithms for operating the transmitter of each radio unit. 
   
   
       4 . A security system for detecting physical intrusion in a monitored area as recited in  claim 1  wherein said circuit establishes a nominal threshold for received signal strength and produces a signal representative of intrusion in the monitored area when the received signal strength exceeds said threshold. 
   
   
       5 . A security system for detecting physical intrusion in a monitored area as recited in  claim 1  wherein said nominal threshold is adjusted continually to compensate for environmental changes. 
   
   
       6 . A security system for detecting physical intrusion in a monitored area as recited in  claim 1  wherein said radio units are arranged such that alternate radio units have an amplifier and no amplifier. 
   
   
       7 . A security system for detecting physical intrusion in a monitored area as recited in  claim 1  wherein said radio units are arranged in a triangular pattern. 
   
   
       8 . A security system for detecting physical intrusion in a monitored area as recited in  claim 1  wherein said radio units are arranged to form an inner ring and an outer ring around the monitored area. 
   
   
       9 . A security system for detecting physical intrusion in a monitored area as recited in  claim 1  wherein said radio units include narrow band, low data rate, low power radios. 
   
   
       10 . A security system for detecting physical intrusion in a monitored area as recited in  claim 1  wherein the same transmissions from the transmitters are used to detect intrusions and to transmit detection status to the base station.