Critical
among those are the problems of power management. An important distinction
between wireless sensor networks and most existing systems is the tremendous
gap between the energy available to a sensor node and that required for its
long-term unattended operation. A typical sensor node such as ones from the
Mica family [8, 9] can last 3??“5 days on a pair of AA batteries in its fully
active mode. In real life applications, though, we would like a sensor network
(comprised of these motes) to last at least a few months. The story is not very
di?®erent with other platforms. The question then is: How can we fill this huge
energy gap? The approaches and techniques applied to fill this energy gap are
collectively referred to as Power Management in wireless sensor networks.
Always-On and Always-o?® Applications of WSN: Applications of
WSNs are broadly divided into two categories ??” always-on and always-o?®. In
an always-on application, it is necessary to monitor the environment continuously
because the events of interest can occur at any time. In most of these
applications, it is also required to notify a base station of an event as soon
as it is observed so that retaliatory actions (or preventive measures) can be
taken quickly. Examples of such applications are intrusion detection [2], where
intruders can breach a protected region any time, shooter localization [23],
where shooting by a sniper can occur anytime, and radiation detection [4],
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