To the best
of our knowledge, there have been no studies of how much lifetime extension
can be achieved for always-on sensor networks by using fine-grained power
management schemes alone.
In this chapter, we address the following question: How long can an alwayson
sensor network last if only a minimal number of sensor nodes are deployed
so that all the deployed nodes are required to be always active to provide the
desired level of monitoring? We show that an always-on sensor network can
also achieve comparable lifetime extensions as an always-o?® sensor network
by using only fine-grained power management schemes. We describe several
fine-grained power management schemes (e.g., hierarchical sensing, low power
listening [20]), where selected components of a sensor node are put to sleep
while still meeting the continuous monitoring and instantaneous notification
requirements (notifying a base station of an event as soon as it occurs) of an
always-on application. We show by using derivations and concrete numbers
the extent of lifetime extensions that can be achieved with these fine-grained
power management schemes.
As a case study, we analyze the lifetime of ExScal [2] ??” a wireless sensor
network deployed to detect and classify intruders of di?®erent kinds3. Our
analysis reveals that using low power listening [20] can extend the ExScal
lifetime from three days to eight days (Section 4.4). Using hierarchical sensing
3 The ExScal network (consisting of close to 1000 wireless sensor nodes) was deployed
on the ground in December 2004 to demonstrate the proof of concept.
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