Dario Pompili

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Communication and Coordination in Wireless
Multimedia Sensor and Actor Networks

• Dario Pompili
• Rutgers, The State University of New Jersey
• Electrical and Computer Engineering Department

Pervasive Computing Workshop CoRE Building
Rutgers Busch Campus October 19, 2007
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Wireless Sensor and Actor Networks
I.F. Akyildiz and I. H. Kasimoglu, Wireless
Sensor and Actor Networks Research Challenges,
Ad Hoc Networks Journal (Elsevier), pp.351-367,
Oct. 2004.
Task Manager Node
Sink
Sensor/Actor Field
Sensors
Actors
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Wireless Sensor and Actor Networks (WSANs)

• Sensors
• Passive elements that sense physical phenomena
  from the environment
• Limited energy, processing and communication
  capabilities
• Actors
• Active elements capable of acting on the
  environment
• Higher processing and communication capabilities
• Less constrained energy resources (longer battery
  life or constant power source)

Sensors Actors
WSANs
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Actors
pan/tilt cameras, water sprinklers, robotic arms
Networked Robots
Autonomous Underwater Vehicles (AUVs)
Unmanned aerial vehicles (UAVs)
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WSAN Applications

• Environmental Applications
• Detecting and extinguishing forest fire, ocean
  sampling
• Microclimate control in buildings
• In case of very high or low temperature values,
  trigger the audio alarm actors in that area
• Agricultural Applications
• Monitor the humidity of a terrain and control
  irrigation
• Distributed Robotics Sensor Network
• (Mobile) robots dispersed throughout a sensor
  network
• Surveillance, monitoring, plume detection
• Pursuit-evasion game
• Rescue missions in disaster areas

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A Sensor Network Increases the Visibility of the
Team
A team of actors with onboard sensors
A team of actors with a sensor network WSANs
B. Sinopoli et al., Distributed Control
Applications Within Sensor Networks, Proc. of
the IEEE, 2003.
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A Coordination Framework for WSANs

• A framework for coordination and communication
  problems in static WSANs
• SENSOR-ACTOR COORDINATION
• Which sensors communicate with which actors?
• How to optimally establish data paths
• How to trade off energy consumption for increased
  RELIABILITY -gt percentage of packets received
  within a given latency bound
• ACTOR-ACTOR COORDINATION
• Which actor(s) perform the action?
• Optimal Solution
• Real-time Localized Auction

T. Melodia, D. Pompili, C. Gungor, I. F.
Akyildiz, A Distributed Coordination Framework
for WSANs, ACM MOBIHOC05, May 2005 T. Melodia,
D. Pompili, C. Gungor, I. F. Akyildiz,
Communication and Coordination in WSANs, IEEE
Transactions on Mobile Computing, 2007
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Sensor-Actor Coordination

• Objectives
• Establish data paths between sensors and actors
• Meet energy efficiency and real-time
  requirements
• Question
• To which actor does each sensor send its data?
• What are the optimal trees from sensors to
  actors?
• Our Solution
• Event Driven Clustering with Multiple Actors

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Event-Driven Clustering with Multiple Actors
Event Area
Event Occurs Sensor-Actor Coordination
Event-Driven Clustering
What is the optimal clustering strategy?How can
we develop a practical distributed algorithm to
achieve this?
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Distributed Protocol

• Objectives of the distributed protocol
• Establish sensor-actor data paths
• Cluster the sensors in the event area
• Find the optimal working point of the network,
  i.e.
• rgtrth (reliability over the threshold)
• Minimum energy consumption
• Based on Geographical Routing
• Based on feedback messages from actors
• Actor calculates reliability r and broadcasts its
  value to the sensors

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Evolution of States for a Sensor
Legend Event Transition Probability
speed-up
start-up
idle
aggregation
Event
TransitionProbability
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Example path establishment
nodes establish paths according to the two-hop
rule (start-up state)
idlestart-up state
an event occurs
Another actor is too far away and thus not
energy efficient for any of the nodes in the
event area
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Example low reliability
Some sensors switch to the speed-up state and
select as next hop the closest node to the actor
? reduce latency
The actor advertises low reliability (rltrth)
idlestart-up statespeed-up state
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Example high reliability
Some sensors switch to the aggregation state and
select as next hop the closest node already in
the tree ? reduce energy consumption
The actor advertises high reliability (rgtrth)
idlestart-up statespeed-up
stateaggregation state
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Actor-Actor Coordination

• Objective
• Select the best actor(s) in terms of action
  completion time and energy consumption to perform
  the action
• Challenges
• Which actor(s) should execute which action(s)?
• How should the multi-actor task allocation be
  done?
• Static Actors Model

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Overlapping Areas
Collector of data from a group of sensors
Non-Overlapping area (only actor 1 can act here)
actor 2
actor 1
Action range
actor 3
Overlapping area (actors 1 and 3 can act here)
Overlapping area (actors 1 and 2 can act here)
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Actor-Actor Coordination Problems

• For an Overlapping Area, actor-actor coordination
  problem
• Selecting a subset of actors
• Adjusting action power levels ? Maximize the
  residual energy and complete the action within
  the action completion bound
• For a Non-Overlapping Area, actor-actor
  coordination problem
• Adjust action power levels
• ? Maximize the residual energy

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Actor-Actor Coordination

• Optimal Solution
• Actor-actor coordination problem formulated as a
  Residual Energy Maximization Problem using Mixed
  Integer Non-Linear Programming (MINLP)
• Distributed Solution
• Real-Time Localized Auction-Based Mechanism

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Example Monitoring Application
2. Wireless, battery powered actor cameras are
woken-up on demand 3. Actors coordinate to
allocate tasks and scan the monitored area
Pan/tilt camera actors
Pan/tilt camera actors
Pan/tilt camera actors
1. Sensors detect movement or sound
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Mobile Actors Considered Scenario
Actor-Actor Coordination Event Reconstruction
Sensor-Actor Coordination actors are equivalent
recipients
Event occurs in the monitored area
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Actor-Actor Coordination
SubArea 1.1
Event area 1
SubArea 1.2
Distributed Task Allocation 1. How many actors
are needed? 2. Coalition Formation - Which actors
are best fit?
SubArea 1.3
Defined action actors should move to the event
area
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Actor-Actor Coordination
SubArea 1.1
Event area 1
SubArea 1.2
SubArea 1.3
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A Communication Architecture for Mobile WSANs

• Mobility Management
• Location Updating
• Location Prediction
• Sensor-Actor Coordination and Communication
• Which actor?
• What is the best path to reach it?
• Actor-Actor Coordination
• Task Assignment
• Team Formation Task Allocation

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Mobility Management

• Objective accurately track the position of
  actors
• At any time, each sensor should be aware of the
  position of its recipient actor
• Combination of two strategies
• Location Updating
• Each actor periodically broadcasts its position
  to sensors
• Location Prediction
• Sensors proactively estimate the location of
  their neighboring actors based on an actor
  movement model
• Less energy consuming (communication is more
  energy-consuming than simple computations)
• We propose a hybrid strategy based on Location
  Prediction and Prediction-based Location Updating

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Prediction-based Location Updates - Example
Step k Actor measures its position Yk and
checks if
SEND UPDATE
Position predicted by the sensors at step k
Step k-1 Actor measures its position Yk-1 and
sends update
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A Multimedia Sensor-Actor Testbed The Floor
Monitoring Application
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Actor Architecture
Stargate Board
Acroname GARCIA
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Stargate Garcia Multimedia Mobile ACTOR

• Mobility
• Onboard IR Sensors
• Pan-tilt Camera
• Connects to a MICAz network
• 802.11 connectivity for actor-actor communication
• Onboard Linux Operating System
• Controls movement
• Sensor-actor coordination
• Actor-actor coordination

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Floor Monitoring Application
Scalar Sensors (MICAz)
Multimedia Sensors
Multimedia Actor with pan-tilt camera
Storage and Computation Hub
Streaming Video
Central Sink
Room 2
Central Sink
Storage and Computation Hub
Room 1