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An Energy-Efficient Unequal Clustering Mechanismfor Wireless Sensor Networks

Chengfa Li, Mao Ye, Guihai ChenState Key Laboratory for Novel Software Technology

Nanjing UniversityJie Wu

Department of Computer Science and EngineeringFlorida Atlantic University

MASS 2005Speaker: Sheng-Wen Chang

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Outline

Introduction The EEUC Mechanism Simulation Conclusions

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Introduction --- Background

Clustering provides an effective way for prolong the lifetime of the WSNs

Using equal size of clusters to balance traffic overhead

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Introduction --- Background

Within a clustering organization Intra-cluster communication can be

single-hop or multi-hop

Inter-cluster communication Single-hop: LEACH Multi-hop: HEED (Infocom 2004)

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Introduction --- LEACH

CHs farther away from the BS must transmit packets over longdistances than those of CHs closer to the BS

Cluster Head

Cluster member

BS

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Introduction --- LEACH

M. Ye, C. Li,  G. H. Chen, and J. Wu,"EECS: An Energy Efficient Clustering Scheme in Wireless Sensor Networks(International Journal of Ad Hoc & Sensor Wireless Networks, 2005)

Cluster header

BS

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Introduction --- HEED

The initial probability for each node to become a tentative CH depends on its residual energy

Final CHs are selected according to the cost

Cluster Head

Cluster member

BS

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Introduction --- HEED

The role of cluster head is usually periodically rotated among nodes

Not balance the energy consumption among CHs

Cluster Head

Cluster member

BS

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Introduction --- HEED

Hop spots problem In each round, CHs closer to the BS are burdened

with heavy relay traffic and tend to die early

Cluster Head

Cluster member

BS

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Introduction --- Motivations and Goals

Motivations Using unequal clustering mechanism to solve

hot spot problem among CHs in each round Clusters closer to the BS have smaller sizes

than those farther away form the BS

Goals Balances the energy consumption Prolong network lifetime

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EEUC --- Assumptions

Sensors uniformly deploy over a sensor field

Sensors and a BS are all stationary Sensors can use power control A node can compute the approximate

distance to another node Based on the received signal strength

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EEUC --- Overview

CHs closer to the BS support smaller cluster sizes More clusters are produced closer to the BS

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EEUC --- Overview

Unequal Clustering Algorithm CHs are selected by localized

competition

Inter-cluster Multi-hop Routing A CH chooses a relay CH

Adjacent CH’s residual energy Its distance to the BS

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EEUC --- Unequal Clustering Algorithm

The BS broadcasts a “hello” message to all nodes

Each node computes the distanceto the BS

Several tentative CHs are selected to compete for final CHs

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EEUC --- Unequal Clustering Algorithm

If Si becomes a tentative CH, Si has a competition range Rcomp

If Si becomes a CH at the end of the competition, there will not be another CH within Si ‘s competition diameter

S3

S4

R4

R3

S2S1

R2R1

S1and S2 can be CHs

S3 or S4 can be a CH

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EEUC --- Unequal Clustering Algorithm

The node’s Rcomp should be decrease as its distance to the BS decreases

is the maximum competition radius c is a constant coefficient between 0 and 1 and

controls Rcomp range

d (si, BS) dmax : si.Rcomp= dmin : si.Rcomp=

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EEUC --- Unequal Clustering Algorithm

The broadcast radius of every control message is

Each tentative CH broadcasts a COMPETE_HEAD_MSG Competition radius Residual energy

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EEUC --- Unequal Clustering Algorithm

Each tentative CH maintains a set SCH

of its “adjacent” tentative CH Tentative head sj is an “adjacent” n

ode of si

Si

Sj

RjRi

SjSi

Rj Ri

sj is in si’s competition diameter orsi is in sj’s competition diameter

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EEUC --- Unequal Clustering Algorithm

Each tentative CH checks its SCH and makes a decision whether it can the final CH

Si’s residual energy is more than all the nodes in its SCH It will win the competition Broadcast a FINAL_HEAD_MSG to inform its a

djacent tentative CHs

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EEUC --- Unequal Clustering Algorithm

A B

If A receives a FINAL_HEAD_MSG from B, A will give up the competition immediately

A informs all nodes in its SCH by broadcasting a QUIT_ELECTION_MSG

C

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EEUC --- Unequal Clustering Algorithm

A B

C receives a QUIT_ELECTION_MSG form A C will remove A from its SCH

C

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EEUC --- Unequal Clustering Algorithm

Each CH broadcasts a CH_ADV_MSG across the network area Node ID Residual energy Distance to the BS

Each ordinary node joins its closest CH

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EEUC --- Inter-cluster Multi-hop Routing

A threshold TD_MAX into our multi-hop forwarding model

If a CH’s distance to the BS is smaller than TD_MAX It transmits its data to the BS directly

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EEUC --- Inter-cluster Multi-hop Routing

A CH chooses a node to forwarding its data from its candidate set RCH More residual energy Smallest distance between the CH and the Relay

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Simulation

Network coverage: (0,0)~(200,200)m

BS location: (100,250)m Number of nodes: 400 : 90m c=0.5 TD_MAX=150m

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Simulation

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SimulationToo many clusters will be produced closer to the BS

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Simulation The first node dies

The last node dies

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Conclusions

Propose a novel energy-efficient clustering mechanism for WSNs

The hot spots problem between CHs is solved

The EEUC mechanism improves the lifetime over LEACH and HEED