A clusterhead is associated with each cluster for co-ordinating MAC
and routing, as well as for aggregating the data collected by the nodes in that
cluster. Nodes may use multi-hopping to send their data to the cluster head.
Instead of using clustering, it is possible to have a hierarchy in which the nodes
send their measured data directly to the sink using multi-hopping, and the
intermediate nodes aggregate the data on a per-hop basis. Clustering o?®ers
a natural way of gathering information over smaller regions, and aggregating
the information by exploiting the spatial correlation. On the other hand a
flat hierarchy allows for hop-by-hop aggregation of data as it travels toward
the sink. A network may use either of the two approaches. Following are
some of the design problems and their corresponding solutions as have been
proposed in the recent literature. Except for the problem of energy-e?±cient
routing discussed in Subsection 5.2, the rest of the problems pertain mainly to
networks that use clustering. Energy-e?±cient routing is an important problem
whenever multi-hop communication is used in the network. Hence we first
focus on energy-e?±cient routing.
Energy-e?±cient Routing
In periodic data gathering sensor networks, data flows regularly from sensor
nodes to the sink during the lifetime of the network. For typical wireless
transceivers, the majority of the battery energy expenditure is on communication.
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