  Information freshness and high energy-efficiency are key requirements for
sensor nodes serving Industrial Internet of Things (IIoT) applications, where a
sink node must collect informative data before a deadline to control an
external element. Pull-based communication is an interesting approach for
optimizing information freshness and saving wasteful energy. To this end, we
apply Content-based Wake-up (CoWu), in which the sink can activate a subset of
nodes observing informative data at the time that wake-up signal is received.
In this case, the timing of the wake-up signal plays an important role: early
transmission leads to high reliability in data collection, but the received
data may become obsolete by the deadline, while later transmission ensures a
higher timeliness of the sensed data, but some nodes might not manage to
communicate their data before the deadline. This letter investigates the timing
for data collection using CoWu and characterizes the gain of CoWu. The obtained
numerical results show that CoWu improves accuracy, while reducing energy
consumption by about 75% with respect to round-robin scheduling.
