ICOM 6505: Wireless Networks Wireless Sensor Networks

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ICOM 6505 Wireless Networks- Wireless Sensor
Networks -

• By Dr. Kejie Lu
• Department of Electronic and Computer Engineering
• Spring 2008

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Wireless Sensor Networks

• Sensor Network Technology Advancements
• Sensors nodes are very close or in the phenomenon
• Sensor nodes have local processing capability
• Sensor nodes can be randomly and rapidly deployed
  even in places inaccessible for humans
• Sensor nodes can organize themselves to
  communicate with an access point
• Sensor nodes can collaboratively work

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Sensors and Sensor Technologies

• The differences of sensor networks from other
  wireless ad hoc networks
• Number of sensor nodes in a sensor network can be
  several orders of magnitude higher than nodes in
  an ad hoc network.
• Sensor nodes are densely deployed. 
• Sensor nodes are prone to failures. 
• The topology of a sensor network changes very
  frequently. 

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Sensors and Sensor Technologies

• The differences of sensor networks from other
  wireless ad hoc networks (Contd)
• Sensor nodes mainly use broadcast communication
  paradigm whereas most ad hoc networks are based
  on point-to-point communications.
• Sensor nodes are limited in power, computational
  capacities, and memory. 
• Sensor nodes may not have global identification
  (ID) because of the large amount of overhead and
  large number of sensors.

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Sensor Applications

• The development of wireless sensor network
  technology is of great national importance by
  virtue of critical applications
• Sensor networks provide the ability to gather
  accurate and reliable information? enabling early
  warnings ?and rapid coordinated responses to
  potential threats
• This encompasses the ability to enhance national
  security from hostile threats as well as the
  ability to save lives through environmental
  monitoring of natural disasters (Preventive
  Measure)
• Environmental sustainability can also be improved
  through sensor network monitoring, by protecting
  valuable resources from overuse or damage, as
  well as being able to collect valuable
  information previously considered too difficult
  and too costly (Maintenance)

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Sensor Networks Applications

• Sensors can monitor ambient conditions including
• Temperature
• Humidity
• Vehicular movement
• Lightning condition
• Pressure
• Soil makeup
• Noise levels
• The presence or absence of certain kinds of
  objects
• Mechanical stress levels on attached objects, and
• Current characteristics (speed, direction, size)
  of an object

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Sensor Networks Applications

• Some of the sensor network application areas
• Military
• Environmental
• Health
• Home
• Disaster relief 
• Space exploration
• Chemical processing
• Other commercial applications

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Sensor Networks Applications

• Characterization of Sensors application
• Continuous sensing
• Event detection
• Location sensing

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Sensor Network Topology

• A sensor network is an array of sensors of
  diverse type interconnected by a communications
  network.
• Sensor data is shared between the sensors and
  used as input to a distributed estimation system
  which aims to extract useful information from the
  available sensor data
• Includes
• Sensor nodes
• Actuator nodes
• Collector
• Gateway
• Wireless link

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Wireless Sensor Networks
sensor node (snode)
actuator (anode)
collector (cnode)
wireless link
Internet, Satellite, etc
Users
Task Manager
Proxy Server
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Sensor Network Topology

• Topology change
• Pre-deployment and deployment phase
• Post deployment phase
• Re-deployment of additional nodes

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Sensor Network Topology

• Sensor networks can be deployed by
• dropping from a plane
• delivering in an artillery shell, rocket or
  missile
• throwing by a catapult (from a ship board, etc.)
• placing in factory
• being placed one by one by a human or a robot

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Sensor Network Topology

• Initial deployment scheme must
• reduce installation cost
• eliminate the need for any pre-organization and
  pre-planning
• increase the flexibility of arrangement, and
• promote self organization and fault tolerance

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Sensor Network Topology

• After deployment topology changes are due to
  change in sensor nodes
• position
• reachability (due to jamming, noise, moving
  obstacles, etc.)
• available energy
• malfunctioning
• task details

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Illustration of A Sensor Network and Backbone
Infrastructure
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Sensor Network Applications For Wetland Monitoring
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Sensor Nodes
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Sensor Nodes
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Sensor Node Hardware

• Small
• Low power
• Low bit rate
• High density
• Low cost (dispensable)
• Autonomous
• Adaptive

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Sensor Nodes Characteristics
1980s-1990s 2000-2003 2010 Manufacturer cust
om contractors Crossbow, Sensoria, Dust, Inc,
and Ember, etc others Size large shoe
box small shoe box dust particle Weight kilogra
ms grams negligible Architecture separate
sensing, proc., integrated integrated comm.
units Topology point-to-point, star client
server, peer-to-peer peer-to-peer Power
supply large batteries AA batteries solar hour
s, days, longer days-to-weeks months-to-years De
ployment vehicle placed or air hand-emplaced embe
dded, drop single sensors sprinkled left
behind Reference C. Chong, S.P.
Kumar, Sensor Networks Evolution,
Opportunities, and Challenges, Proceedings of
IEEE, Vol. 91, No. 8, August 2003.
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Environment for Sensor Networks

• Sensor networks may work
• in busy intersections
• in the interior of a large machinery
• at the bottom of an ocean
• inside a twister
• at the surface of an ocean
• in a biologically or chemically contaminated
  field

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Environment for Sensor Networks

• Sensor networks may work (Contd)
• in a battlefield beyond the enemy lines
• in a house or a large building
• in a large warehouse
• attached to animals
• attached to fast moving vehicles, and
• in a drain or river moving with current

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Important Design Factors

• Fault tolerance ( of failures)
• Scalability ( of sensor nodes)
• Production Costs
• Operating Environment
• Sensor Network Topology
• Hardware Constraints
• Transmission Media, and
• Power Consumption

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Scalability

• May reach millions of sensor nodes in studying
  a phenomenon or stimuli
• Density of sensor nodes is high
• Schemes tend to form clusters
• Each cluster has a coverage area of less than 10
  meter
• Each cluster may have several to hundred sensor
  nodes

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Production Cost

• Volume must be high to achieve economy of scale
• PicoNode less than a dollar
• Bluetooth system more than five dollars
• COTS ranges from 25 to 200

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Power Consumption

• In existing wireless networks, QoS is more
  important than power efficiency.
• In sensor networks, power conservation is of
  utmost importance. Hence, novel power-aware
  protocols and algorithms are needed
• Network lifetime depends on battery lifetime
• Limited power resources (1 V)
• Generally irreplaceable

Power Consumption
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Power Consumption

• Power consumption in a sensor network can be
  divided into three domains
• Communication
• Transmission and reception energy costs are
  nearly the same
• Transceiver circuitry has both active and
  start-up power consumption
• Data Processing
• Sensing

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Networks Architecture
Sensor Node
A
Sensor Field
B
Sink
E
C
F
Internet, Satellite, etc
D
Look at a scheme how to transmit wirelessly the
collected sensor data efficiently by routing
data back to the sink in consideration of power,
delay minimization whilst maximizing the radio
resource utilization
Task Manager
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Networks Model

• Used by sink and all sensor nodes,
• Combines power and routing awareness,
• Integrates data with networking protocols,
• Communicates power efficiently through
• wireless medium, and
• Promotes cooperative efforts.

Application Layer
Transport Layer
Task Management Plane
Mobility Management Plane
Network Layer
Power Management Plane
Data Link Layer
Physical Layer