Image Processing Reference
In-Depth Information
where
k is the round
E i
(
t
)
is the current energy of node i
E total
(
t
)
is the sum of the current energy of all the nodes
Using this probability assignment, nodes with higher energy also have a greater probability of
becoming cluster heads. However, this assignment requires knowledge of the energy of the other
nodes in order to calculate E total
, and acquisition of this knowledge itself would require a lot of
energy. he solution proposed is that a node only collects the average energy for the cluster it belongs
to and approximates the total energy by multiplying this value by the number of nodes N .
Another modiication of the election phase is suggested in [Han], where a deterministic factor is
introduced in the probabilistic cluster-head selection. Here too the basic idea is to consider energy in
cluster-head elections, in order to achieve a longer lifetime through clever cluster-head selection. he
proposed approach is to modify the threshold equation T
(
t
)
, considering both the residual energy
and the number of times a node has been a cluster head. he proposed threshold is
(
n
)
p
E n _current
E n _max
T
(
n
)
=
(.)
new
mod p
p
(
r
)
where E n _current and E n _max are, respectively, the current and the initial energy levels. Using this
new threshold, simulations show a lifetime increase between % and % over the original LEACH
protocol. However, there is a nonnegligible drawback, as the probability of becoming a cluster head
decreases as the energy for each node decreases, so the number of cluster heads will decrease until
the network remains inactive, even if there are still nodes capable of transmitting to the sink node.
Hence a further enhancement is proposed, with the threshold
p
E n _current
E n _max +(
r s div
E n _current
E n _max )]
T
(
n
)
=
[
p )(
(.)
new
mod p
p
(
r
)
where r s is the number of consecutive rounds in which the node has not been a cluster head. Using
this metric, after 
p rounds during which a node is not a cluster head, the threshold reaches the same
value it would have in the original protocol. In this way, clever cluster-head selection still increases
the lifetime of the WSN, without causing network blockage.
/
7.5.2.1 LEACH-Centralized (LEACH-C)
The LEACH-C protocol described in [Hei] proposes a further improvement for LEACH regarding
cluster formation. In fact, the distributed protocol in LEACH does not offer guarantees on either
the good placement or the correct percentage of cluster heads. So the basic idea of LEACH-C is to
run a centralized clustering algorithm while maintaining the same data transmission phase. All the
computations are performed at the BS, which has to know the position and energy of every node.
In this way, the BS will only consider nodes with sufficient energy as possible candidates to become
clusterheads.heobjectiveoftheclusteringalgorithmistominimizethepowerconsumptionof
the non-cluster-head nodes, so the optimal selection is mapped on a simulated annealing problem
in which the total sum of the squared distance between the non-cluster-head nodes and the closest
cluster head is minimized. Once the selection is performed, the BS broadcasts a message containing
thecluster-headIDofeachnode.herestofprotocolisthesameasLEACH.
7.5.2.2 Hybrid Energy-Efficient Distributed Clustering (HEED) Protocol
The HEED protocol presented in [You] is an energy-efficient clustering protocol designed for
WSNs that can be used in a generic cluster-based application or routing protocol. The aim of the
Search WWH ::




Custom Search