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A routing algorithm for gathering correlated data in the sensor network is
proposed by Luo [11], which is based on an adaptive fusion Steiner tree. A
routing tree among sensors, which have data to be collected, is constructed
keeping in mind the fusion cost, transmission cost, and data structure.
5.3 Modeling Data Aggregation within WSN
The tasks, which are performed by a sensor, consist mainly of three opera-
tions: sense, process, and transmit. We model these three tasks within a sen-
sor as a task-flow graph (TFG) as shown in Figure 5.2. Each task ( S i , P i , and T i )
has an execution time, which indicates the duration of time to complete the
task and these values are deterministic for now. However, the starting and
finishing times for each task are unknown, and our goal is to schedule the
starting and finishing times with an acceptable load to be handled by the
base station. Thus, scheduling all the tasks within the WSN should coor-
dinate among sensors and we have proposed to combine all TFGs into a
STFG as illustrated in Figure 5.3. The graph, STFG (V,E), consists of vertices
(tasks) and a set of direct edges representing the flow of tasks. The STFG is
an acyclic graph.
To start the process of scheduling, we need to insert two dummy nodes
representing the starting and finishing of all tasks. These two dummy nodes
(SN and FN) require zero execution time.
Sense
( S i )
Process
( P i )
Transmit
( T i )
Figure 5.2
A task-flow graph (TFG) for a sensor i .
 
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