It is obvious that sensors chosen to be
clusterheads would consume more energy, because they have more communication
load. Thus, these clusterheads will die quickly and the overall system
lifetime may be reduced. LEACH [10] addressed this problem by using randomized
rotation of the ???clusterheads??? and the corresponding clusters, which
can distribute the work load evenly among sensors in the network.
352
Chpater 14 Performance Comparison of Clustering Schemes
The operation of LEACH is broken up into rounds. Each round includes
two phases, a set-up phase, during which the clusters are formed, and a steadystate
phase, during which data is transmitted to the base stations.
Initially, each sensor node decides whether to become a clusterhead or
not based on the suggested percentage of clusterheads in the sensor network,
and the number of times the node has been a clusterhead so far. Each node
randomly chooses a number between 0 and 1. If the number is less than the
threshold T(n), the node becomes a clusterhead for the current round. The
threshold is computed as
T(n) = ( P
1??’P?—(r mod 1
P )
if n 2 G,
0 otherwise.
where P is the percentage of clusterheads given as an input, r is the current
round, and G is the set of nodes that have not been clusterheads in the last
1
P rounds.
Each node that has elected itself a clusterhead for the current round will
broadcast an advertisement message to the rest of the nodes.
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