The prediction-based scheme uses some movement prediction techniques, such
as [12], to predict the next location of the target. As shown in Figure 8(b), only
nodes in the predicted area need to join the tree.
After deciding which node should join the tree, the root sends a notification message
to the grid head of the grid containing those nodes. When the grid head
receives the notification, it wakes up all nodes in the grid, and nodes can join the
convey tree. If some nodes need to be pruned, the root sends a prune message to
the grid head of the grid in which all nodes should be removed. The grid head
receiving the prune message broadcasts it to nodes in its grid immediately, and
those nodes can leave the tree and go to sleep.
(a) (b)
Fig. 8. Tree expansion and pruning. (a) The conservative scheme. (b) The prediction-based
scheme.
??? Tree Reconfiguration: While the target keeps moving, it may move far away
from the root of the initial convey tree. If nodes keep forwarding sensing data
to the root of the original tree, packets have to be forwarded throughout multiple
hops, and will consume more energy while the target moves farther away.
Therefore reconstructing a tree to achieve more energy efficient aggregation is
desired.
DCTC triggers the tree reconfiguration when the distance between the root and
the target exceeds a threshold. When the distance exceeds a threshold, one of the
nodes that is closest to the target is selected randomly, and the current root sends
a migration request to the new root.
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