One way to achieve this is to organize the
network into smaller sub-networks called clusters. Each cluster can be then
managed autonomously. Such a hierarchy results in lower routing overheads,
and could also be used for in-network aggregation of the measured data. The
clusters themselves could consist of nodes with di?®erent hardware capabilities.
Within each cluster, the responsibilities of co-ordinating MAC and routing,
as well as data aggregation could be assigned to nodes with special hardware
[35].
3.6 Node Deployment versus Placement
Depending on the application, sensor nodes could either be deployed randomly
over the area of interest (battlefield surveillance, forest fire detection, etc.), or
the nodes could be placed deterministically at specified locations (temperature
and light monitoring in buildings, seismic monitoring of bridges and buildings,
etc.). When nodes can be placed deterministically, ensuring network connectivity
is relatively easy. However, when we do not have control over node
locations (random deployment), a certain extent of over-provisioning of nodes
is required to ensure network connectivity [21].
10
3.7 Node Mobility and Dynamic Topology
In many cases, the sensor nodes have very little, or no mobility. However, there
are some applications such as monitoring of military personnel and equipment,
and wildlife monitoring which involve node mobility. When the nodes are
mobile, the topology of the network changes, and it may be necessary to
update the routing information of the nodes.
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