The preferred scheduling
technique in WSNs is TDMA, since it does not require a complex hardware
design and allows inactive nodes to enter the sleep state. In this section we
3.1 Low-Energy Adaptive Clustering Hierarchy (LEACH)
Protocol
In LEACH [3], the network topology contains a single sink node and many
sensor nodes that sample the environment at a constant rate and send their
data to the sink. The network has a hierarchical organization. The network is
divided into clusters, and each cluster has associated a cluster head node. Each
node in the cluster sends its sensed data to the cluster head where it belongs.
The cluster head aggregates the data packets received into a single packet,
which is transmitted to the sink. For this operation, a perfect correlation
among the received data packets is assumed.
The network activity is organized into rounds, where each round has two
phases: initialization phase and steady-state phase. During the initialization
phase, clusterheads are elected and new clusters are formed. For each round,
new nodes act as cluster heads in order to evenly distribute the energy consumption
among network nodes, so that nodes will die randomly at approximately
the same rate. Each cluster head coordinates the activity of the sensors
in its cluster and establishes the TDMA schedule. This schedule is then broadcasted
to all the nodes in the cluster. During the steady-state phase, all nodes
transmit their sensed data according to the TDMA schedule.
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