Energy-Driven Adaptive
Clustering Hierarchy (EDACH)
for Wireless Sensor Networks
Kyung Tae Kim, Hee Yong Youn
(Sungkyunkwan University)
Research supported by the “uAuto” Project
Outline
•
•
•
•
Introduction
System Model
Proposed Protocol - EDACH
Performance Evaluation
WSN
• Wireless sensor network enables the
collection of useful information in real life.
• It is composed of hundreds or thousands of
sensor nodes.
• Since sensor nodes carry constrained power
source, power conservation is a critical
design issue for routing protocol.
Clustering-based Routing
• Selects a set of cluster-heads among the
nodes in the network, and clusters the rest
of nodes (member nodes) with the clusterheads
• 2 clustering-based routing protocol referred
to:
– LEACH
– EDACH
LEACH
• Low-Energy Adaptive Clustering Hierarchy,
a protocol proposed to solve the energy
consumption problem
• Employs randomized rotation of the clusterheads to evenly distribute the energy load
among the sensor nodes in the network
EDACH
• Energy-Driven Adaptive Clustering
Hierarchy, an enhanced version of LEACH
• Increases the lifetime and reliability of
sensor network in the presence of faults at
the cluster-head
Outline
•
•
•
•
Introduction
System Model
Proposed Protocol - EDACH
Performance Evaluation
Single-Hop Clustered Network
• Nodes and clusterheads are homogenous
• Communication over
wireless link
Energy Model of a Sensor
• 1st order radio model
• A radio dissipates Eelec
(e.g. 50nJ/bit) to run
the transmitter or
receiver circuitry and
εamp (e.g. 100pJ/bit) for
the transmitter
amplifier
Fault Model
• Consider only data
transmission faults of
cluster-head
Outline
•
•
•
•
Introduction
System Model
Proposed Protocol - EDACH
Performance Evaluation
LEACH Overview
• The operation is divided into rounds.
• Each of these rounds consists of 2 phases: a
set-up phase and a steady-state phase.
• During the set-up phase cluster-heads are
determined and the clusters are organized.
• During the steady-state phase data transference to the base station occurs.
EDACH Overview
• Periodic operation of the following 2 phases:
a set-up phase and a self-organized data
collection and transmission phase.
• The set-up phase is identical to LEACH.
• The 2nd phase is modified to deal with the
possible problem that cluster-heads in the
LEACH have no sufficient energy to carry
out the duty of cluster-head.
Enhancement
• If a cluster encounters a problematic clusterhead, then a proxy is selected to operate in
replace of the original cluster-head.
Set-up Phase
• In order to select cluster-heads, each node
chooses a random number between 0 and 1.
• If the number is smaller than a threshold,
the node becomes a cluster-head for the
current round.
Set-up Phase
• The threshold is set as:
P


T n    1  P  (r mod 1 )
P

0
if n  G
otherwise
where P is the desired percentage of cluster-heads, r is the
current round, and G is the set of nodes that have not been
cluster-heads in the last 1/P rounds.
• Every node becomes a cluster-head exactly
once within 1/P rounds.
Set-up Phase
• After selection, every selected cluster-head
advertises its token by CSMA/CA MAC
protocol to all its neighbors.
• Comparing the signal strength of the token,
non cluster-head nodes choose among the
strongest and broadcasts an answer packet
including node’s position and remaining
energy also by CSMA/CA.
Set-up State
• At last, the clusterhead node creates a
TDMA schedule
telling each node when
it can transmit.
Self-organized Data Collection
and Transmission Phase
• Starts after the set-up phase.
• Every nodes collected local data, and sends
the packet to the cluster-head in its allocated
transmission time.
• No doubt that cluster-heads consumes much
more power and more likely to suffer from
depletion.
Ways to Save the Energy
• For member nodes, by using the minimal
amount of energy to transmit according to
the signal strength of the token received
• For member nodes, by turning off until its
allocated transmission time
• A Cluster-head aggregates the data gathered
before sending it to the base station.
Difference
• A threshold value ETH is used as a measure
for deciding if the current cluster-head has
become obsolete.
2
ECH ( j )  Eelec  k j   amp  k j  d CH
( j)
ETH
1 k
  ECH ( j )
k j 1
where kj is the length of the aggregated message in the j-th
cluster-head, dCH is the distance between cluster-head and
the base station
Difference
• Once the energy of a cluster-head drops
below the threshold, the proxy node
selection process begins.
• A cluster-head of EDACH maintains a table
of remaining energy and nodes’ position of
its members so it can select a member node
to be a proxy node by comparing the 2
factors.
Proxy Node Determination
Indicator Control Message
Advertisement Process
Outline
•
•
•
•
Introduction
System Model
Proposed Protocol - EDACH
Performance Evaluation
Network Lifetime
Energy
(J/node)
0.25
0.5
Protocol
The round a
node begins
to die
The round the
last node dies
Direct
41
97
LEACH
191
317
EDACH
276
411
Direct
91
184
LEACH
453
623
EDACH
786
1015
Number of Alive Sensors as the
round proceeds with 0.25J/node
Location of Alive (Circle) and
Dead (Dot) Sensor Nodes
Conclusion
• EDACH outperforms the LEACH more
significantly when the initial energy is
relatively high.
• The residual energy is well balanced among
all the sensors because the protocol select
the most capable node to be a proxy when
facing problematic cluster-head.
• The dead nodes of EDACH well dispersed.