Therefore LEACH randomly selects different
nodes as clusterheads in each round to avoid this problem.
The operation of LEACH is divided into rounds, where each round contains a
set-up phase and a steady-phase. In the set-up phase, each node decides whether
or not to become a clusterhead by choosing a random number between 0 and 1. If
the number is less than a threshold, than the node becomes a clusterhead. Node n
calculates the threshold as follows:
T(n) = ?? P
1??’P?—(r mod 1
P ) if n 2 G,
0 otherwise,
where P is the percentage of nodes that are clusterheads, r is the current round, and
G is the set of nodes that have not been selected as clusterheads in the last 1
P rounds.
Using this threshold function, all nodes take turns to be clusterheads in a random
order. After all nodes have been clusterheads exactly once, i.e., after 1
p rounds, all
nodes start over to participate in the clusterhead selection process again.
The node that elects itself as the clusterhead broadcasts an advertisement message
to notify other nodes. Nodes that are not clusterheads receive the clusterhead
advertisement messages. During the set-up phase, each non-clusterhead node may
receive multiple advertisement messages. Assuming the radio channel is symmetric,
choosing the clusterhead with the strongest signal strength minimizes the required
energy to transmit packets. Therefore nodes join the cluster of the clusterhead from
which they received the advertisement with the highest radio signal strength.
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