The clusterheads represent the entire cluster to the rest
of the network, and are chosen periodically according to di?®erent algorithms.
This allows the routing algorithms to break the routing process into separate
subsections, similar to IP based routing, regardless of how many nodes actually
exist in the ad hoc network. This scheme is very flexible and allows
for scalability. These algorithms must be carefully tuned to make sure that
the nodes inside the clusters can e?±ciently communicate with the clusterhead
and that the clusterhead can in turn communicate e?±ciently with the other
clusterheads. Since the clusterhead may not be chosen based on its geographic
distance from the other clusters, one cannot guarantee that a cluster can always
directly communicate with another cluster e?±ciently. In e?®ect, the extra
layer of abstraction takes away from the precision of the routing algorithms
which works on top of the hierarchy. Hierarchical based protocols are still
an excellent tool in the design of a sensor network. The hierarchy concept is
very robust and has many applications in sensor networks besides routing, for
instance to minimize interference and deploy frequency reuse.
Low Energy Adaptive Clustering Hierarchy (LEACH) [19] is a classical hierarchical
protocol designed specifically for sensor networks. LEACH assumes
that all nodes are within the transmission distance of the sink. Clustering is
utilized to allow for scalability and a rotation of clusterheads is configured to
distribute the load.
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