Accurate and timely detection of intruders was critical to ExScal. Accuracy
had priority over timeliness.What good is a network that gives false detections
quickly? Therefore, the network was required to have a low false alarm rate. If
the detection message does not reach the base station quickly, an intruder may
compromise the asset being protected by the sensor network. Therefore, low
latency of event notification was also critical to ExScal. ExScal was required
to achieve both low false alarm rate and low latency of detection in the face of
unavoidable failures (both hardware and software). We refer the readers to [3]
for a list of hardware, software, deployment, localization, and other failures
encountered in the ExScal demonstration.
Finally, low human involvement is a key to the operation of a large scale
sensor network. Imagine the e?®ort and time needed if one thousand sensor
nodes deployed over a 1 km long region have to be touched individually by
a human for some reason (e.g., to turn them on and o?®). Therefore, a large
4 The appropriate notion of coverage for intrusion detection application is barrier
coverage [18], where sensors form a barrier for intruders. For a precise definition
of the concept of barrier coverage and several interesting results, including the
optimal topology to achieve k-barrier coverage, we refer the readers to [18].
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scale sensor network such as the ExScal needed to provide easy operation, require
minimal or no touching of individual sensor nodes, and allow monitoring
of network health and reconfiguration of network parameters from a remote
central location.
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