In sender-based wakeup, the period and the
local frequency of wakeup events are the main contributors. In both cases,
such collisions could either result in a longer than expected wakeup delay or
lead to energy ine?±ciencies, depending on the specifics of the actual protocol.
5.2 Interaction with MAC
Although they allow for a very low power sleep mode, asynchronous schemes
typically have a sizable overhead associated with the wakeup event. It has
been realized that due to this overhead, it is ine?±cient to use these schemes
when wakeup events are relatively frequent [12]. This basically means that
asynchronous wakeup protocols are not well suited as pure MAC protocols.
Instead, knowledge of expected packet arrivals can be used to schedule designated
wakeup times in the future [12] [14] [30] [33], which essentially corresponds
to starting a local TDMA schedule. In principle, other MAC solutions
could be used as well.
In addition, a successful wakeup event can be used as a synchronization
point for nodes to learn each other clocks. This could potentially allow a reduction
of wakeup overhead since the wakeup becomes more synchronized. This
synchronization between nodes will eventually degrade due to clock drifts,
slowly moving the wakeup regime from synchronous to asynchronous.Whether
synchronicity should be maintained, or it is more e?±cient to allow the system
to gradually revert to an asynchronous wakeup solution, depends on the
specifics of the application.
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