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Figure 1.2. Hop-by-Hop Routing
However, in certain situations, it is inefficient for each node to forward the cap-
tured raw data directly to the sink node, as this could lead to early exhaustion of valu-
able resources (battery, memory, and computation ability) of each intermediate routing
node. Hence, to overcome this issue, the network is further divided into clusters and
each cluster has a cluster head. Each cluster head is responsible for locally aggregating
data from its cluster nodes and then forwarding it to its sink node. Furthermore, cluster
heads can preprocess the raw data before sending it to the sink node.
Depending on the way data is aggregated by sensor nodes, WSN architectures can
be classified into homogenous, heterogeneous, and hybrid sensor networks (Nakayama
et al. 2007).
1.3.1 Homogenous Sensor Networks
In a homogenous network architecture, the cluster heads and the ordinary sensor nodes
have the same computational, storage, and communication capabilities as a sink node.
In this architecture, the network topology determines the method of data aggregation.
Usually, flat and hierarchical architectures (Figure 1.3 and Figure 1.4) are used in a
homogenous architecture (Rajagopalan and Varshney 2006).
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