Lai
where terrorists can explode a simple radiological dispersion device at any
time.
In an always-o?® application, it is not necessary to monitor the environment
continuously; periodic monitoring is enough because the environment does
not change very abruptly. Examples of such applications are habitat monitoring
[21], where the environment of a bird nest does not change abruptly, and
the monitoring of subgalacial bed formation [19], where the glaciers do not
change their position or temperature abruptly.
Classification of Power Management Approaches: An application
faces the problem of power management if the active life of the sensor nodes
comprising a WSN is less than the desired life of the network. In such a case,
we need to find ways to extend the lifetime of the network. We divide the
approaches for doing so in two major categories:
??? Fine-Grained Power Management: This approach extends the active lifetime
of individual sensor nodes by exploiting redundancy already existing
in the network. For example, in an always-o?® application it is not necessary
to sample the environment continuously. So, all the sensor nodes can be
put to sleep, to wake up only periodically for sampling the environment.
As another example, in an always-on application, selected components of
sensor nodes (such as the radio) can be put to sleep to be woken up either
on demand or periodically, while still meeting the monitoring and notifi-
cation requirements of the application.
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