Cohen, Joshua Goldberg, and Jaudelice C. de Oliveira
not be distributed evenly since some nodes might lie very far from the sink
and some might be very close, or even a few adjacent nodes could become
clusterheads. To more evenly distribute the power consumption of the network,
in Equation 2 the threshold for each node is scaled by the proportion of
residual energy in a node. This scaling can lead to cases where the threshold
is too small and no clusterhead will be chosen. To avoid this situation an additional
term is added to increase the fraction of the threshold according to
the number of rounds in which the individual node has not yet been chosen
as a clusterhead.
In every round, the nodes generate a random number between 0 and 1 and
compare it to the threshold. A random number above the threshold means
that the node will become a clusterhead. Once a node decides to be a clusterhead,
an advertisement is broadcast to the the rest of the nodes. Nodes
which have not decided to become clusterheads choose a clusterhead according
to the received signal strength. Since all nodes are within transmission
distance of the sink, the transmitting clusterheads are cycled evenly and the
energy consumption is evenly distributed. This protocol is very scalable but
requires some additional work to maintain an e?±cient route to the sink if the
clusterheads are not within transmission range.
TEEN [12], APTEEN [13], PEGASIS [11], Energy Aware Routing (EAR)
for Cluster-Based Sensor Networks [29], and self-organizing protocol [25] are
other examples of hierarchical protocols.
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