Image Processing Reference
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both the algorithm and the simulations only consider energy consumption due to transmission,
i.e., no idle energy consumption or the possible use of low-power/sleep states are taken into account.
While this protocol achieves interesting results from the theoretical point of view, in a real network
there are also some drawbacks. For example, it lacks flexibility, as packets could be of variable size and
the MAC layer could have some nondeterministic behavior, so it is not always simple to accurately
estimate the energy required by each packet. In addition, this protocol requires topology knowledge,
which in large WSNs is not simple to achieve.
7.5 Cluster-Based Energy-Efficient Routing Protocols
7.5.1 Low Energy-Adaptive Cluster Hierarchy Protocol
The LEACH protocol [Hei] is a milestone for cluster-based protocols for WSNs, which has the
objective of reducing power consumption by decreasing the transmission power and duty cycle of
sensornodes.heprotocolisdesignedforWSNswheretheBSisixedanddistantfromthesensor
nodes. In addition, the nodes are assumed to be homogeneous and energy-constrained. he design
principles of the LEACH protocol are
Localized coordination and control for both setup and operational phases
Random rotation of cluster heads
Data aggregation techniques to reduce communication costs
Nodes are grouped in clusters, each containing a cluster-head node. Non-cluster-head nodes only
transmit to their cluster heads, while cluster heads perform long-distance transmission directly to
the sink node.
The authors assume a first-order radio model. In this model, a radio dissipates E elec
=
 nJ
/
bit to
m for the transmitter ampliier. he
radioshavepowercontrolandcanconsumetheminimumrequiredenergytoreachtheintended
destinations. he radios can be turned off to avoid receiving unintended transmissions. An r energy
lossisusedduetochanneltransmission.
The equations to calculate transmission costs and receiving costs for a k -bit message and a distance
d are as follows:
run the transmitter or receiver circuitry and ε amp
=
 pJ
/
bit
/
Transmission
E Tx
(
k , d
)=
E Tx
(
k
)+
E Tx
(
k , d
)
elec
amp
(.)
d
E Tx
(
k , d
)=
E elec
k
+
ε amp
k
Receiving
E Rx
(
k
)=
E Rx
(
k
)
elec
(.)
E Rx
(
k
)=
E elec
k
As receiving a message is not a low-cost operation, the number of receptions and transmissions for
each message should be minimized.
According to this model, direct transmissions to the BS can be more efficient than the minimum
transmission energy (MTE) routing protocol (in which each node sends a message to the closest
node on the way to the BS) if the ratio E elec
ε amp and the number of hops is sufficiently high.
However, the cluster-based approach is more efficient than direct transmissions, as only a small per-
centage of nodes, i.e., the cluster heads, need to perform highly expensive long-distance transmissions
to the sink. The majority of nodes can instead perform less expensive transmissions, as they only
need to communicate with the cluster head, which is usually much closer than the sink. On the other
/
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