91%.
Organization of the Chapter. In Section 2, we discuss several finegrained
power management schemes that can be used to extend the lifetime of
a wireless sensor network deployed for an always-on application. In Section 3,
we provide an overview of the ExScal application, the sensor platform used
in ExScal, and major factors that a?®ect the network lifetime of ExScal. In
Section 4, we analyze the lifetime of ExScal, illustrating the lifetime extensions
achievable by using various fine-grained power management schemes. Section 5
concludes the paper.
2 Fine-grained Power Management Schemes
In this section, we discuss some fine-grained power management techniques
that can be applied to extend the lifetime of a WSN deployed for an always-on
application. All of these schemes exploit some redundancy already existing in
the network to extend network lifetime without a?®ecting the quality of service
o?®ered by the network.
2.1 Low Power Listening (LPL)
In an always-on application such as ExScal, most of the time there is no
communication in the network. However, the radio can not be turned o?® on
all sensor nodes, because as soon as an event occurs, the event notification
message should be quickly propagated to a base station using radios on other
sensor nodes that sit in the path of the sensor detecting an event and the base
station. Therefore, ideally, we would like to have a radio that can wake up
from the sleep mode by hearing a transmission from a neighbor so that it can
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be put to sleep when there is no communication in its neighborhood.
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