In general, ID-based schemes have better throughput
in mobile environments than the topology-based schemes, since it is unlikely
that node degrees will remain stable, and a topology-based scheme would
require frequent cluster head updates.
2.2 Topology-based Heuristic
The topology-based clustering was originally proposed in [16]. Each node
broadcasts its ID to the nodes that are within its transmission range. Two
nodes are considered to be a neighbor of each other if one node lies within
the transmission range of the other node. The node with maximum number
of neighbors (i.e., maximum degree) is chosen as a clusterhead. The neighbors
of a clusterhead become members of that cluster and can no longer participate
in the election process. Since no clusterheads are directly linked, only
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Yadi Ma and Maggie Cheng
one clusterhead is allowed per cluster. Any two nodes in a cluster are at most
two-hops away since the clusterhead is directly linked to each of its neighbors
in the cluster. Basically, each node either becomes a clusterhead or remains a
neighbor of a clusterhead.
The performance of a topology-based scheme like WCA ([12]) is largely
dependent on the network stability. When nodes move around, the number
of nodes in a cluster will change. As the number of nodes in a cluster is increased,
the throughput drops and hence a gradual degradation in the system
performance is observed. The rea?±liation of nodes is quite often due to node
movements and as a result, the current clusterhead may not be re-elected to
be a clusterhead.
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