One could envision a heterogeneous
sensor network, where specialized nodes are designed and deployed
solely to create a wakeup infrastructure. Since these nodes only require limited
functionality, they could be substantially cheaper and therefore could be
deployed in a higher density.
Due to the distributed nature of sensor networks, dealing with range disparity
is a non-trivial problem. If it is dealt with appropriately, on-demand
paging is an extremely powerful technique to enable low-power consumption
in the dormant state [15]. Synchronous and asynchronous wakeup essentially
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Chapter 8 Wakeup Strategies in Wireless Sensor Networks
Fig. 5. Solutions to range disparity.
aim at mimicking the behavior of a low-power paging channel by duty cycling
a regular radio. It is also possible to apply such duty cycling on top of
the on-demand paging, to combine the gains of both approaches and enable
ultra-low energy consumption [13].
4 Synchronous Wakeup
The principle of synchronous wakeup is allowing nodes to duty cycle their
radio in a coordinated, i.e. synchronous, fashion. The benefit of such coordination
is that wakeup and MAC are naturally separated in time as they
can be assigned to distinct time intervals. As such, it is often easy to design
synchronous schemes to be out-of-band.
Before discussing schemes that were proposed specifically for sensor networks,
the power saving options of two existing standards proposed by the
IEEE will be briefly described first in the next subsection.
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