Movement-Assisted Sensor Deployment

Author : Guiling Wang, Guohong Cao, Tom La Porta

Presenter : Young-Hwan Kim

Contents

Introduction

Technical preliminary

Movement-assisted sensor deployment protocols

Performance evaluations

Discussion and future work

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Sensor DeploymentStationary protocol

Environment is known and under control

Dynamic centralized protocol Environment is unknown and or hostile

Ex) remote harsh fields, disaster areas and battle fields A powerful cluster head is need Problem of single point failure

Dynamic distributed self-deployment protocol

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Problem statementProblem statement

Given the target area, how to maximize the sensor coverage with less time, movement distance and message complexity

Processing 1) discovering the coverage holes – Voronoi diagram 2) target positions of these sensors, where should move - VEC, VOR, and Minimax protocols

Term Coverage holes – the area not covered by any sensor Target positions – the points need to sensing

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Voronoi DiagramVoronoi polygon

Voronoi polygon of O as is the set of Voronoi vertices of O is the set of Voronoi edges of O is the set of Voronoi neighbors of O

example

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Voronoi DiagramSensor deployment protocol are based on Voronoi diagramsEach sensor is enclosed by a Voronoi polygonPolygons together cover the target fieldEach sensor can examine the coverage hole locallyEach sensor needs to know its Voronoi neighbors

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Three Deployment ProtocolsBased on Voronoi diagram

the location information of Itself and neighbors

heuristic Runs iteratively until it satisfy

Distributed Self-deployment protocols

Difference VEC pushes sensors away from a densely covered area VOR pulls sensors to the sparsely covered area Minimax moves sensors to their local center area

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VEC(The VECtor-based Algorithm)The attributes of electro-magnetic particles

Terms is the distance between two sensors( , ) is the average distance two sensors ( beforehand ) is the distance between a sensor and boundary

The virtual force between two sensors ( , ) ( ) Case1. Voronoi polygon not completely

away from each other Case2. Voronoi polygon completely (One)

The other sensor will pushed away Case3. Voronoi polygon completely (Two)

Virtual force is 0 ( Not pushed )

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VECThe virtual forces between a sensors and boundary( )

away from boundary

Overall virtual force on sensor is the vector summationAlgorithm

Movement adjustment

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VECThe execution of VEC

35 sensors / 50m x 50m / random deployment Coverage : 75.7% -> 92.2% -> 94.7%

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VOR(The VORonoi-based Algorithm)Greedy algorithm which tries to fix the largest holeIf a sensor detects the existence of coverage holes

-> it will move toward its farthest Voronoi vertex Where is equal to the sensing range

Fig. VOR

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VORLimit

The maximum moving distance is half of the communication range

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VORAlgorithm

Oscillation control

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VORThe execution of VOR

Coverage : 75.7% -> 89.2% -> 95.6%

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Minimax AlgorithmWhy minimax?

Distance of the farthest Voronoi vertex is minimized Regular shaped Voronoi polygon

Compare with VOR Similar to VOR, moving closer to the farthest Voronoi

vertex Minimax considers more information and it is more

conservative

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Minimax Algorithm

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Minimax Algorithm

To find the minimax point, we only need to find all the circumcircles of any two and any three Voronoi vertices

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Minimax AlgorithmAlgorithm

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Minimax AlgorithmThe execution of Minimax

Coverage : 75.7% -> 92.7% -> 96.5%

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Termination & OptimizationTermination

1) the best coverage is obtained 2) reached the specified maximum round 3) a threshold . Defined as the minimum increase in

coverage

Optimization When the initial deployment of sensors may form

clusters Coverage low, deployment time prolong

The algorithm ‘explodes’ the cluster to scatter the sensors apart

Only runs in the first round

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Minimax Algorithm

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Performance EvaluationsTwo aspects : 1)deployment quality, 2)cost

1) is determined by the number of rounds needed and the time of each round

2) is determined by the sensor cost and the energy consumption of the deployment

Various system parameters Sensor density, field size, topology, communication

range,

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Performance Evaluations

Proposed protocol good!Why VEC worst?

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Performance Evaluations

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Performance Evaluations

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Performance Evaluations

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Discussion

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To maximize the sensing coverage based on Voronoi diagrams

Designed three distributed protocols to move mobile sensors form densely deployed areas

Simulation results verified the effectiveness of protocols

Future Work

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Optimal Movement

Communication

Sensing Area

Extend to Large Sensor Networks