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cluster heads. Hence, nodes with lower energy levels simply capture the required raw
data and forward it to their respective cluster heads. Usually, the cluster heads possess
more processing and storage capacity than any ordinary sensor node.
In the case of a highly dynamic and a decentralized environment, nodes with
higher energy levels can take responsibility for a cluster head and nodes with lower
energy levels can be the cluster nodes. Furthermore, adopting this architecture will
not only increase the energy efficiency of the network, it will also balance traffic load
with an increase in size of the network. In certain situations, data aggregation can be
performed at the cluster heads instead of the sink node to improve the efficiency of the
entire network.
1.3.2 Heterogeneous Sensor Networks
In a heterogeneous sensor network, the sink node or base station can be mobile (Shah
et al. 2003; Chatzigiannakis et al. 2006). Hence, the mobile sink node can move ran-
domly to any of the sensing regions and collect data by interacting closely with the
sensor nodes. In addition, the sink's mobility will increase the overall energy level of
the system.
1.4 Architecture of Sensor Nodes
A typical sensor node consists of a sensing unit, a processing unit, and a transceiver
(Figure 1.5). The sensing unit consists of actual sensors, and it is the only interface to
the outside environment.
Figure 1.5. Architecture of Sensor Node
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