On the Coverage Problem in Video-based Wireless Sensor Networks

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On the Coverage Problem in Video-based Wireless
Sensor Networks

• Stanislava Soro Wendi Heinzelman
• University of Rochester

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Outline

• Motivation
• Problem statement
• Overview of DAPR
• DAPR in video-based WSNs
• Simulation results
• Conclusions

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Motivation

• Telepresence application for VWSN
• enables user to experience being fully present at
  a physically remote location
• network consists of wireless nodes equipped with
  very low-power cameras
• user can navigate and virtually move around in
  the monitored space

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Motivation (II)

• Distinct features of video-based WSN over
  traditional WSN
• Very large amount of highly correlated data
• Capturing images of objects that are not
  necessarily in cameras vicinity
• Sensing range is replaced with FoV (field of
  view)

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Problem of interest

• Coverage preservation in WSNs
• PEAS, DAPR, CCP.
• How do already existing coverage protocols for
  WSNs behave in video-based WSNs?
• We assume floorplan monitoring monitoring of
  scene in one plane
• Each point of monitored area should be covered by
  at least one camera
• We analyze how an application-aware routing
  protocol (DAPR) behaves in this design space

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Overview of DAPR in WSN

• DAPR-Distributed Activation based on
  Predetermined Routes
• Coverage preserving protocol that avoids the data
  routing through critical nodes
• Proposes application-aware approach each nodes
  importance for sensing application is evaluated
• C(Sj) area monitored by sensor Sj
• Monitored area is divided into grid, where the
  center of each grid cell is given as (x,y)
• Total energy for monitoring location (x,y)

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Overview of DAPR in WSN (II)
Application cost of node S1
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Overview of DAPR in WSN (III)

• Application cost

• Link cost between two nodes

• Cost of a route from node to sink

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DAPR in camera-based WSNs

• Two planes
• Cameras plane location of point given as (x,y)
• Cameras FoV plane location of point given as
  (xc,yc)

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DAPR in camera-based WSNs (II)

• Every location (xc,yc) on monitoring plane
  characterized by total energy

• Final application cost

• Total routing cost for every camera

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Traditional energy-aware routing

• Willingness of every node to route data

• This cost does not consider the importance of a
  node for sensing application

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Comparison of application-aware routing in WSN
and video-based WSN
Traditional wireless sensor network
Video-based wireless sensor network
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Application-aware routing in wireless sensor
networks

• Requested part of the scene determines the
  locations of all potentially active sensor nodes
• The application cost tells us
• how redundantly the node is covered
• how important node is as a router

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Application-aware routing in video-based WSNs

• Mismatch between cameras physical positions and
  cameras FoV
• Here, the application cost evaluates the node
• only from the coverage perspective
• but NOT from the routing perspective
• Example a node can be well covered (small
  application cost), but located in scarcely
  deployed area makes it important as a router

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Application-aware routing in video-based WSN (II)

• Hotspot problem appears more easily
• Potentially active nodes can be far from each
  other
• Select to be active a node with smallest
  cumulative path cost usually node closest to
  the base station
• Energy-aware cost outperforms application-aware
  cost
• Balanced energy spent among the nodes prolongs
  the lifetime of each node
• The loss of nodes is more uniform over the area

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Combined application and routing cost

• Every camera node validated through two separate
  cost functions

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Combined application and routing cost

• Reduces the energy consumption, compared to
  application-aware routing

• With a change in number of nodes, the same
  relation between three protocols persist

CEA(Sj) CAA(Sj) Ctotal(Sj)
Average power/path (mW) 0.1091 0.1251 0.1121
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Conclusions

• Application-aware routing protocol gives
  different results in traditional and video-based
  WSNs
• Found that coverage and routing problem exist as
  two separate problems in video-based WSNs
• Further study of this problem
• Explore further combined cost function
• Explore how other coverage preserving protocols
  behaves in video WSNs
• Three dimensional coverage problem
• Consider collaboration of cameras
• Consider the ability of cameras to capture image
  with different resolution