The common characteristic
of all these applications is the infrequency of occurrence of the events of
interest. A WSN deployed for such an application is expected to be inactive
most of the time, bursting into activity when an event is detected. Then, the
WSN has to promptly convey an event report to the sink(s). An event report is
expected to contain some location information about the event, and a description
of the nature of the event. An important problem for such networks, at
the application level, is to minimize the probability of false alarms. Generally
speaking, detection of an event based on consensus between a group of sensors
is likely to produce a lower false alarm rate than detection of an event using
a single sensor. However, from the point of view of networking, the significant
design problem is that of routing the event report on the fly, to the sink, once
the process of event detection is over.
2.2 Data Gathering and Periodic Reporting
WSN applications in this class include, monitoring the environmental conditions
a?®ecting crops or livestock, monitoring temperature, humidity and lighting
in o?±ce buildings, and so on. These monitoring modules could even be
combined with actuator modules which can control, for instance, the amount
of fertilizer in the soil, or the amount of cooling or heating in a building, based
on distributed sensor measurements. In these cases, each sensor is expected
to constantly produce some amount of data which has to be conveyed to the
sink(s).
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