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the proposed tree based data aggregation protocols
and describe their strengths and weaknesses. In
section 3 we explain our protocol FFDA in detail
along with the factor EAT and in section 4 we
evaluate the performance of FFDA algorithm and
compare it with some of recently proposed
algorithms.
2 RELATED WORKS
There are several tree-based aggregation algorithms
and each of them considers one parameter as the
main parameter to determine the aggregation tree’s
root and then construct the spanning tree based on
the selected root. Some of them select the node with
highest remaining energy among all nodes as root
while others consider the shortest distance to BS as
the main parameter. Moreover, many different
methods and parameters are used to construct the
spanning tree, either as a single factor or as a
combination of factors.
For example, Espan protocol (Lee and Wong,
2005) selects the node with the highest remaining
energy within the entire network as tree’s root, then
each node selects the closest neighbor to root as its
parent and if there are more than one neighbor with
same distance then the node with highest remaining
energy is selected as parent. So distance and
remaining energy are two parameters used in Espan
protocol to construct the aggregation tree while
distance has higher priority. This way it is possible
that a node with low remaining energy level is
selected as parent because of short distance to root,
therefore after data aggregation is done, this node
loses its energy quickly because of high traffic
passing through it and it leads to incomplete
coverage and system failure.
In LPT (Lee and Wong, 2005) nodes with higher
remaining energy are chosen as parents in
aggregation tree in order to increase the lifetime of
nodes with high traffic. This way a node far away
from root may be selected as parent because of its
high remaining energy levels but it will be drained
quickly due to long distance transmission energy
consumption.
In the proposed algorithm by Mohajerzadeh et al.
(2008) they had introduced an efficient algorithm in
which nearly most of the problems we described in
Espan and LPT are solved, and the simulation
results has shown their algorithm has better
performance than Espan and LPT algorithms in
terms of both first node die and system's lifetime.
But there is a big disadvantage in their protocol that
causes an unbalanced energy consumption
throughout the network. In presented algorithm by
Mohajerzadeh et al. (2008) the main factor to choose
a node as root for spanning tree is residual energy of
nodes, so a node with highest remaining energy
(HRE) is selected as root.
In the following section we describe the
drawbacks of HRE factor and introduce the new
factor EAT, then we will explain the proposed
protocol.
3 PROPOSED ALGORITHM
As mentioned earlier, in the beginning of each round
we have to select a node as root for spanning tree,
and then construct the tree based on selected root
until every single node is covered. In (Mohajerzadeh
et al., 2008), LPT and many other tree based
protocols, the node with highest remaining energy is
selected as root. while this method causes an
unbalanced network in terms of energy, we replaced
it with the factor EAT as a new parameter to keep
the remaining energy of nodes more balanced
through the process and thus prolong the lifetime of
the system and delay the first node die. In the
following section we describe the factor EAT in
details and then we represent the complete protocol.
3.1 EAT Factor
Suppose 5 nodes named N1 to N5 with initial energy
of 1300, 1300, 1800, 1600 and 1700 are respectively
positioned in a field. Distances between nodes and
BS are 16, 18, 15, 20 and 10 respectively. One of
these nodes is selected as root depending on which
factor we use to determine the root node. Then all
the nodes constitute a spanning tree to gather the
captured data and send the data towards the root,
where the root sends the aggregated data to BS in
order to analyze.
In figure 1 it is shown how the BS and nodes are
positioned in the field. Using the proposed algorithm
in Mohajerzadeh et al. (2008) the node number 3 is
selected as root since it has the highest remaining
energy among nodes. This may seem logical since
sending packets to BS drains the energy of root node
specially when BS is positioned far away from field,
but this is not the best way to select the root amongst
the nodes because it ignores the distances between
nodes and BS in root selection.
Therefore we introduce the new factor EAT and
replace the HRE factor with it. We calculate EAT
FFDA - A Tree based Energy Aware Data Aggregation Protocol In Wireless Sensor Networks
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