Another issue is detecting the start of a new quasi-dormant period, where it
is beneficial to turn theMAC protocol o?® and only resort to a wakeup protocol.
This could be based on a soft timer that fires when no activity is detected
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Curt Schurgers
within a certain time period, or be based on application layer information. A
source node could, for example, indicate that a packet is the last one of an
active communication stream, which is analogous to a termination message in
circuit switching systems.
In addition to the transitions between wakeup and MAC, the problem of
coexistence between these two is important. It is possible that one pair of
nodes is actively communicating information and utilizing a particular MAC
protocol, while other nodes in the vicinity are quasi-dormant and need to be
woken up to establish another communication path. Unlike paging solutions
which are naturally out-of-band, or synchronous wakeup where time division
multiplexing is a logical choice to create an out-of-band solution, the issue
is more complex in asynchronous wakeup. When wakeup and MAC use the
same logical channel (same frequency band, spreading code, etc.), they have to
contend for the same medium. One option is to give wakeup precedence over
regular medium access, for example in a sender-based asynchronous wakeup
scheme [30]. However, while a wakeup event is ongoing, other nodes in the
neighborhood cannot send their data.
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