Mobility Improves Coverage of Sensor Networks

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Mobility Improves Coverage of Sensor Networks
Benyuan Liu, Peter Brass, Olivier Dousse,
Philippe Nain, Don Towsley
Department of Computer Science University of
Massachusetts - Lowell
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Outline

• background and motivation
• mobility improves coverage
• summary and future work

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What is coverage ?

• coverage quality of surveillance of sensor
  network
• how well sensors cover a region of interest ?
• how effective sensor network detect intruders ?
• many different measures area coverage, barrier
  coverage, detection coverage, etc
• important for surveillance sensor net
  applications
• battlefield, infrastructure security

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Mobile sensor networks

• coverage of stationary sensor network intensively
  studied
• sensors can be mobile mounted on robots or move
  with environments

Q How does sensor mobility affect coverage?
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Previous workHoward 02, Zou04, Wang 04

• sensors move to reach stationary configuration
  with better area coverage

• several approaches proposed, different in how to
  compute desired locations for sensors (e.g.,
  potential field, virtual force, etc)

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Our work

• different perspective coverage resulting from
  continuous movement of sensors

• 1. mobility increases covered area
• stationary sensors covered area doesnt change
  over time
• mobile sensors uncovered area may be covered
  later, more area covered over time

• we are interested in area coverage
• area covered at specific time instant t
• area covered over time interval 0, t)
• fraction of time a location is covered

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Our work

• 2. mobility improves intrusion detection
• stationary sensors intruder wont be detected if
  not move or moves along uncovered path
• mobile sensors may be detected by moving sensors

• we are interested in detection time
• time before an intruder is first detected
• measure how quickly sensors detect intruders
• consider stationary and mobile intruders

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Our work

• 3. how should sensors and intruder move?
• intruder moves to maximize its detection time
• sensors minimize the maximum detection time

• we are interested in optimal mobility strategies
• for both sensors and intruders
• game theoretic approach

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Network model

• initial configuration
• sensors are deployed uniformly at random
• sensor density ? sensing range r
• mobility model
• each sensor chooses a random direction ??0, 2?)
  according to distribution
• speed vs ?0, vsmax according to

simple model to obtain insight
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Area coverage

• area coverage at any given time instant unchanged

• uncovered region will be covered, more area will
  
• be covered for a time interval 0,t)

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Tradeoff covered area and covered time

• location alternates between covered and uncovered

• uncovered time
• covered time

fraction of time a point is covered

• appropriate for delay-tolerant applications

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Detection time stationary intruder
Vs

• intruder can be detected by moving sensors
• detection time time before first being detected,
  X
• divide sensors into different classes according
  to direction
• time takes to be first hit (detected) by a class
  i sensor

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Detection time stationary intruder

• detection time smallest hit times among all
  classes
• result

• to guarantee expected detection time smaller than
  T0

can tradeoff sensor density with speed
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Mobile intruder detection time

• convert to reference system where intruder is
  stationary
• detection time

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Mobile intruder optimal strategy

• target maximizes its lifetime

• sensors minimize the maximum detection time

a minimax optimization problem
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Optimal strategy special cases

• sensors choose direction uniformly in 0, 2?)
• intruder stay stationary
• intuition if intruder moves, will hit oncoming
  sensors sooner

• sensors move in same direction
• intruder moves in same direction with same speed
  as sensor

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Optimal strategy solution
?

• sensors choose direction uniformly
• target stay stationary
• intuition if not uniform, intruder will move in
• direction of highest probability density,
  resulting
• in longer detection time

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Summary and future work

• define coverage resulting from sensor mobility
• derive analytical results to provide insight
• future work
• more general mobility and detection model
• collaboration among sensors

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Thank you!