Similarly, to analyze the e?®ect of sounding a buzzer for 1 minute every
hour on the lifetime of ExScal, substitute isensor = 0.292 mA in (6) and use
a new term with a value of 15/60 = 0.3642 mA in the denominator (because
the buzzer draws 15 mA of current on an XSM). By doing so, we find that
an XSM??™s life will decrease from 871.81 hours to 780.38 hours (a decrease of
more than 90 hours of life) as a result of sounding the buzzer for one minute
every hour by the actuator.
5 Conclusion
In this chapter, we discussed several fine-grained power management techniques
that can be used to extend the lifetime of an event-based (always-on)
application of wireless sensor network without requiring any additional sensor
nodes than is absolutely necessary to meet the application??™s monitoring requirements.
We showed using concrete numbers that the lifetime of ExScal ??”
an application of wireless sensor network for intrusion detection and classification,
can be extended by more than 16 times by using low power listening and
hierarchical listening alone, both of which are existing features of the XSM
platform. Contrary to popular belief, we showed that it is possible to achieve
comparable network lifetime extensions for event-based (always-on) applications
as for data gathering (always-o?®) applications, without deploying any
more sensor nodes than are absolutely necessary to meet the application??™s
monitoring requirements.
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