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A Bidding Protocol for Deploying Mobile Sensors

GuilingWang, Guohong Cao, and Tom LaPorta

Department of Computer Science & Engineering

The Pennsylvania State University

ICNP 2003

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Outline

Introduction The bidding protocol Performance evaluation Conclusion and future work

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Introduction

In some harsh environments, manually deploying sensors is impossible – such as during in-building toxic-leaks– Alternative methods may lead to imprecise

placement resulting in coverage holes

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Introduction

Equip each sensor with a motor increases the network cost

– unnecessary when the coverage requirement is not very strict

– sensors can be scattered in the target field relatively uniformly

Deploy a mixture of mobile sensors and static sensors to construct sensor networks

– achieve a balance between sensor cost and coverage

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Introduction-Vironoi diagram-

Vironoi cellVironoi diagram

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The bidding protocol

Static sensors – detect the coverage holes locally– estimate the size of these holes– determine the target position inside the hole

Based on the properties of the Voronoi diagram, – static sensors can find the coverage holes locally – estimate the target location of the mobile sensors

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The bidding protocol

Mobile sensors : hole healing servers– base price: the estimate of generated coverage hole after it

leaves the current place– Mobile sensor only moves to heal another hole if its leaving

will not generate a larger hole than that to be healed

Static sensors are the bidders of the coverage hole healing services

– Their bids are the estimated sizes of the holes they detect – Mobile sensors choose the highest bids and move to the tar

get locations provided by the static sensors

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The bidding protocol

During the initialization, all static sensors broadcast their locations and identities locally

After the initialization period, static sensors broadcast this information again only when new mobile sensors arrive and need this information to construct their own Voronoi cells

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The bidding protocol

: static sensor

: mobile sensor

A

E

E

O

DC

Static sensors construct Vironoi

cell

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The bidding protocol

The bidding protocol runs round by round after the initialization period

Each round consists of three phases– advertisement, bidding , serving

Advertisement – Mobile sensors broadcast their base prices and locations in a local are

a– The base price is set to be zero initially

Bidding – static sensors detect coverage holes locally by examining their Voronoi

cells– If holes exist, they calculate the bids and the target locations for the m

obile sensors– static sensor find a closest mobile sensor whose base price is lower th

an its bid, and sends bidding message to this mobile sensor

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The bidding protocol

Serving– Mobile sensor chooses the highest bid and moves to heal

that coverage hole– The accepted bid will become the new base price of the

mobile sensor After the serving phase, another new round can start

after the mobile sensors broadcast their new locations and new base prices

when no static sensors can give out a bid higher than the base price of the mobile sensors

– protocol terminates

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The bidding protocol

: static sensor

: mobile sensor

A

E

W

O

DC

G

H

J

Broadcast base price

and ID

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The bidding protocol

: static sensor

: mobile sensor

A

E

W

O

DC

G

H

J

Static sensors detect coverage hole

Static sensors bid for mobile sensors

E bids GO bids JW bids H

(bids closest mobile sensor)

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The bidding protocol-bid estimation-

Static sensors construct Voronoi cells considering – static neighbors– mobile neighbors which are not likely to move

when detecting coverage holes, static sensors do not consider those mobile sensors which are about to leave

To construct its Voronoi cell, each sensor first calculates the bisectors of the considered sensors and itself based on the location information

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The bidding protocol-bid estimation-

If there exists a coverage hole, static sensor chooses the farthest Voronoi vertices as the target location of the coming mobile sensor

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o

The bidding protocol-bid estimation-

Na Nb

NcActual

additional coverage

Estimated coverage

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The bidding protocol-Optimize greedy heuristic-

Na

Nb

Nc A

B

C

Max distance

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Duplicate healing

Duplicate healing problem

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Duplicate healing-self-detection algo-

In the advertisement phase, mobile sensors broadcast their locations and base price

If a mobile sensor hears that another mobile sensor in its neighborhood has a higher base price than its own,

– Run the detection algorithm to check whether a duplicate healing has occurred

– If yes, the mobile sensor reduces its base price to zero it will likely to move to cover a different hole

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Performance evaluations

ns-2 (version 2.1b9a) 40 nodes randomly deployment MAC Protocol : 802.11 Routing protocol: DSDV Sensing range: 6 meter Communication range: 20 meter

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Performance evaluations

The number of sensors needed to reach certain coverage under different mobile percentage

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Performance evaluations

The figure shows the number of rounds needed to terminate in the worst case

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Performance evaluations

Duplicate healing number

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Performance evaluations

Average moving distance of mobile sensors

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Conclusion

Propose to deploy a mixture of mobile and static sensors to construct sensor networks to provide the required uniform sensing service in harsh environments

Performance evaluation shows that can increase the coverage significantly with low communication overhead and limited movement

future work – study how obstacles on the field affect the performance, an

d how to deal with non-uniform sensing coverage