Hence it
is necessary to dimension the number of nodes in the network and their communication
range, and also design routing protocols so that sensing coverage
of the entire region of interest is assured. Works in [22, 42] contain results
on network connectivity and sensing coverage in large sensor networks with
random node deployment and/or under possible node failures. E?®ects of shadowing
at the wireless physical layer on network connectivity for a network with
randomly deployed nodes are studied in [4].
5 Class-specific Problems in Sensor Networks
The approach taken by previous survey papers on sensor networks, such as
[2], has been that of discussing the design problems in sensor networks on a
per-problem basis. Ours is the first work that systematically classifies these
networks based on the application characteristics, and then discusses the problems
faced by each class of applications. In what follows, we discuss the past
work that focuses on problems pertaining to each application class.
5.1 Event Detection and Reporting
The objective of sensor networks in this application class is to detect rare
events, such as forest fires or intrusions, and to promptly communicate a
report of such an event to the sink. Due to the infrequency of the events of
interest, the driving design principle in this case is to minimize the energy
consumption due to all the activities other than event reporting. Issues such
as packet collisions or link-layer fairness are not very important, due to the
low tra?±c load.
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