The uncovered
elements in set S3 is only C1, and cost ratio for set S3 is 4/1 = 4. Therefore
S3 is selected at the second step, and all elements are covered.
After the covering sets are decided, the node sends the negative reinforcement to
the nodes whose sets are not selected. Nodes receiving the negative reinforcement
delete the gradients to that node from which the negative reinforcement is received,
therefore they stop sending packets to that node.
6 DCTC
DCTC [8] is a dynamic convey tree collaboration framework that takes advantage
of node collaboration for target tracking. Nodes construct a tree, named a convey
tree, to collect sensing report and collaboratively convey these reports to the root to
provide robust and reliable data. While a target is moving, some nodes may be farther
away from the original root and the energy cost of forwarding the packet to the root
increases. Therefore the convey tree is reconfigured in an efficient way to reduce the
energy consumption.
When a target enters the sensing range of the sensor networks, there may be multiple
sensor nodes detecting the target. If every node generates the report and sends
the data to the sink directly, the network will be flooded by many concurrent traffic
flows, which is not only energy inefficient, but may also increase the detection delay
and reduce the packet delivery ratio. DCTC avoids this problem by constructing a
convey tree that aggregates concurrent sensing reports and collects these reports at
the convey tree root.
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