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Energy-Efficient Self-Organization for Wireless Sensor Networks: A Fully

Distributed approach

Liang Zhao, Xiang Hong, Qilian LiangDepartment of Electrical EngineeringUniversity of Texas at Arlington

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Outline

Introduction to Cluster-based Sensor Networks

LEACH Protocol Review Problem Formulation Expellant Self-Organization Scheme Simulation Conclusion

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Cluster-based Sensor networks(1/2)

Homogeneous versus Heterogeneous Single hop versus Multi-hop

BS

Advantage: Robust to node failures.Drawbacks: (1) High load on cluster head(2) The hardware has to support

(a) long range transmissions(b) complex data computations(c) co-ordination of MAC(d) routing within a cluster.

Advantage: Sensor nodes only requires simple hardware support.

Drawbacks: (1) Less robust to node failure(2) Sensors far from cluster head have

highest energy expenditure(3) Uniform clustering has to be

considered.

Single hop homogeneous networks Single hop heterogeneous networks

BS

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Cluster-based Sensor networks(2/2)

BS

Multi-hop homogeneous networks Multi-hop heterogeneous networks

BS

Sensors near cluster head have highest energy expenditure

Distance from cluster head

Energy Single hopMulti hop

[ Infocom04 , Globecom04 ]

[ 2 * Globecom04 ]

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LEACH Protocol

1. Single hop homogeneous networks

2. Random cluster head rotation

3. Perfect data correlation model– All individual packets from members of the same

cluster can be combined into a single representative packet.

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LEACH Protocol

In LEACH, each node i elects itself

to be a head at the beginning of

round r+1 with probability Pi(t).

(1)

(a) Ci(t) is the indicator function determining whether or not node i has been a head in the most recent (r mod (N/c)) rounds.

(b) c is the desired number of clusters

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(2)

Ei(t) is the current energy of node i

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Problem Formulation

1. N in (1) and Etotal in (2) are global information

2. Too few or too many cluster heads []3. Non-uniform distribution of cluster heads

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Random election

(1) Suppose

(2) All nodes have equal amount of energy,

if N nodes want to elect c heads, then the self-electing probability for each node is

[back]

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Expellant Self-Organization Scheme

Contribution:

Turn the question about “how many clusters should the nodes be partitioned? “

into “What is the appropriate cluster size?”

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[Example]

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Expellant Self-Organization Scheme

ExampleStep 1: Each node broadcasts vital information (energy, location,…etc) at cluster radius Rc (Rc is a predetermined system parameter)

Rc

Step 2: Each node counts its neighbors and broadcasts the number of its neighbors at cluster radius Rc

2

1

2

3

1

1

0

•N is the set of neighbors•B(i) is the number of neighbors of the ith neighbor• r = 0.8 in this paper

Step 3: Each node decides to become cluster head according to its potential and broadcast its claim( Using random back-off to avoid collision)

Potential:

)()1()(max iBmeanriBrBNiNi

Th

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Expellant Self-Organization Scheme

Step 4: Nodes sends “Joint” message to join the nearest cluster head

2

1

2

3

1

1

0

Step 5: Nodes that are outside the neighborhood of existing cluster head forces itself to be a cluster head

“Joint”

[back]

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Simulation

100 nodes Each has 2J initial energy Evenly distributed in a circular region with

diameter 100m Base station located at (125m, 0)

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Radio Energy Dissipation Model

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Optimal c (1/2)

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Optimal c (2/2)

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ESO versus LEACH (1/2)

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ESO versus LEACH (2/2)