On the Coverage Problem in Video- based Wireless Sensor Networks Stanislava Soro Wendi Heinzelman University of Rochester

10/3/2005BASENETS'05 Outline Motivation Problem statement Overview of DAPR DAPR in video-based WSNs Simulation results Conclusions

10/3/2005BASENETS'05 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

10/3/2005BASENETS'05 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 camera’s vicinity  Sensing range is replaced with FoV (field of view)

10/3/2005BASENETS'05 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

10/3/2005BASENETS'05 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 node’s importance for sensing application is evaluated C(S j ) – area monitored by sensor S j 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): (x,y)

10/3/2005BASENETS'05 Overview of DAPR in WSN (II) S2S2 S1S1 S4S4 S3S3 E(S 3 )=5 E(S 1 )=1 E(S 4 )=10 E(S 2 )=2 G A B C D F E Application cost of node S 1

10/3/2005BASENETS'05 Overview of DAPR in WSN (III) Application cost: Link cost between two nodes: Cost of a route from node to sink:

10/3/2005BASENETS'05 DAPR in camera-based WSNs Two planes  Cameras’ plane: location of point given as (x,y)  Cameras’ FoV plane: location of point given as (x c,y c )

10/3/2005BASENETS'05 DAPR in camera-based WSNs (II) Every location (x c,y c ) on monitoring plane characterized by total energy: Final application cost: Total routing cost for every camera:

10/3/2005BASENETS'05 Traditional energy-aware routing Willingness of every node to route data: This cost does not consider the importance of a node for sensing application

10/3/2005BASENETS'05 Comparison of application-aware routing in WSN and video-based WSN Traditional wireless sensor network Video-based wireless sensor network

10/3/2005BASENETS'05 Application-aware routing in wireless sensor networks BS 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

10/3/2005BASENETS'05 Application-aware routing in video- based WSNs BS network’s plane scene plane 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

10/3/2005BASENETS'05 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

10/3/2005BASENETS'05 Combined application and routing cost Every camera node validated through two separate cost functions

10/3/2005BASENETS'05 Combined application and routing cost C EA (Sj)C AA (Sj)C total (Sj) Average power/path (mW) Reduces the energy consumption, compared to application-aware routing With a change in number of nodes, the same relation between three protocols persist

10/3/2005BASENETS'05 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