4.4 Localization and Synchronization
The objective of sensor nodes is to report their measurements to the sink.
Hence it is important for the sink to know the locations at which these measurements
were taken so that future actions can be taken accordingly. This
requires a localization scheme so that the nodes can determine their current
location. Since sensor nodes are small, energy constrained, and often deployed
indoors, GPS-based solutions are not suitable for them. Hence it is necessary
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to devise other means for localization. Time synchronization is also required
so that the measurements can be time-stamped. Synchronization is also useful
in scheduling sleep-wake patterns of the nodes in power-saving algorithms.
However, both localization and synchronization have communication overheads
associated with them, and these tradeo?® issues have been addressed in
several works such as [41, 18, 19].
4.5 Connectivity and Coverage in Unfriendly Terrain
In many sensor network applications, the user does not have complete control
over the placement of each node. Consequently, once the nodes have been
deployed, some of them could end up in locations that are wireless-unfriendly
due to shadowing. Even for applications where the user has control over node
deployment, the nodes could experience bad fades due to changes in the surrounding
environment. Sometimes, nodes could experience temporary or permanent
hardware failure due to changing environmental conditions such as
heat and humidity, and this may impact the network connectivity.
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