The sink might not be directly interested in the individual measurements,
but could require a distributed computation of some function of the
sensor readings. The sensor readings also might need to be attached to some
sort of location information, if the sink is interested in recreating a spatial
profile of the readings.
2.3 Sink-initiated Querying
The monitoring applications mentioned in the previous subsection may also
require the additional feature of sink-initiated querying. In this case, rather
than each sensor periodically reporting its measurements, the sink could query
7 Chapter 1 Design of Large-scale Sensor Networks
Aravind Iyer et al.
a set of sensors for their measurements. This enables the sink to extract information
at a di?®erent resolution or granularity, from di?®erent regions in space.
For instance, consider an application monitoring a manufacturing process. In
case there is any anomalous behavior, the sensors could report such an event
to the sink. Then the sink can query some specific set of sensors to obtain more
information, possibly to confirm the event. Depending on the sensor readings
thus obtained, the sink could trigger the appropriate actuators, or raise an
alarm for human intervention. For the underlying communication protocols,
we need (for example) e?®ective means to address and route data to and from
dynamic sets of sensors.
2.4 Tracking-based Applications
WSNs for tracking have a lot of applications in military or border surveillance
where one is interested in tracking an intruder or the movements of a suspicious
object.
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