Wireless Sensor Networks

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Wireless Sensor Networks

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• PC??????????????????
• Pocket PC????,??????????
• WSN???????????????

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Outline

• General Comments
• Wireless Sensor Network Applications
• Architecture of WSN
• Overview of Sensor Hardware
• Characteristic of WSN
• Our Work

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Outline

• General Comments
• Wireless Sensor Network Applications
• Architecture of WSN
• Overview of Sensor Hardware
• Characteristic of WSN
• Hot Issues
• Our Work

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Sensor network A new research hotspot
August 2003 Business Week projects "Sensors and
Sensor Networks". to be one of 4 Key Technology
Waves of the Future
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Faster, Smaller, Numerous

• Moores Law
• Stuff (transistors, etc) doubling every 1-2
  years

• Bells Law
• New computing class every 10 years

Streaming Data to/from the Physical World
log (people per computer)
year
Source The Mote RevolutionLow Power Wireless
Sensor Network Devices
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Whats are Wireless Sensor Networks

• Wireless networks are usually composed of small,
  low-cost devices that communicate wirelessly and
  have the capabilities of Processing, Sensing and
  Storing
• The purpose is to measure different physical
  parameters in a given environment, in order to
  characterize its properties, or to take decisions
  depending on these measurements.

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Enabling Technologies
Embed numerous distributed devices to monitor and
interact with physical world
Network devices to coordinate and perform
higher-level tasks
Networked
Embedded
Exploitcollaborative Sensing, action
Control system w/ Small form factor Untethered
nodes
Sensing
Tightly coupled to physical world
Exploit spatially and temporally dense, in situ,
sensing and actuation
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Outline

• General Comments
• Wireless Sensor Network Applications
• Architecture of WSN
• Overview of Sensor Hardware
• Characteristic of WSN
• Hot Issues
• OUR WORK

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Wireless Sensor Network Applications

• Military Applications
• Environmental Applications
• Health Applications
• Home Applications
• Industrial Applications
• Other Commercial Applications

Application ltgt WSN
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Military Applications

• enemy tracking, battlefield surveillance
• target detection and classification

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An ExampleCounter Sniper System
Using the arrival times of the acoustic events
at different sensor locations, the shooter
position can be accurately calculated using the
speed of sound and the location of the sensors.
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• sensors and vehicles are deployed to perform
  collaborative monitoring tasks over a given area
  under ocean.
• Large number of sensor nodes collect data from
  the ocean and forward to a master node.

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Industrial Applications
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From talk of Yunhao Luo
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Outline

• General Comments
• Wireless Sensor Network Applications
• Architecture of WSN
• Overview of Sensor Hardware
• Characteristic of WSN
• Hot Issues
• OUR WORK

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Architecture of WSN

• Sensor nodes are scattered in a sensor
  field(object field)
• Sensor nodes can self organize to form a sensor
  network
• Data are collected by these scattered nodes and
  routed back to the sink in a multi-hop way
• The user communicate with the sink via Internet

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Architecture of WSN(cont'd)

• nodes are still stationary.
• multiple, mobile sinks defined as users.
• sinks may collect data at any time, any place.

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Architecture of WSN(cont'd)
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From Talk of YunHao Luo
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A general work process of WSN
Deploy
Organize into network
Sensing and monitoring
Data collection and dissemination
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Outline

• General Comments
• Wireless Sensor Network Applications
• Architecture of WSN
• Overview of Sensor Hardware
• Characteristic of WSN
• Hot Issues
• OUR WORK

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Sensor Hardware

• Fundamental Components
• Various Sensing,Processing,Storing,
  Transceiver,Power
• Application dependent components
• Locating, Mobilizer, Power generator

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Sensor Node Samples
AWAIRS I UCLA/RSC 1998 Geophone, DS/SS Radio,
strongARM, Multi-hop networks
LWIM III UCLA, 1996 Geophone, RFM radio, PIC,
star network
Sensor Mote UCB, 2000 RFM radio, Atmel
Medusa, MK-2 UCLA NESL 2002
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Mote Evolution
Source The Mote RevolutionLow Power Wireless
Sensor Network Devices
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Outline

• General Comments
• Wireless Sensor Network Applications
• Architecture of WSN
• Overview of Sensor Hardware
• Characteristic of WSN
• Hot Issues
• OUR WORK

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Characteristic of WSN

• Resource Constraints
• battery equipped,recharging the batteries is
  impossible or unfeasible
• Radio and embedded CPU
• Self configuring
• Randomly deployed, unattended.
• Dynamic Topology
• Data centric
• Different from traditional network
• Unique traffic model
• Application specific

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Power Consumption

• Power is of most important and directly
  influencing the lifetime of WSN
• Consumption in three domains
• Sensing, communication and data processing
• Energy consumed by Comm. is dominating
• The energy cost of transmitting 1Kb a distance of
  100 m is approximately the same as that for
  executing 3 million instructions by a 100 million
  instructions per second (MIPS)/W processor.

k
S
D
Tx/Rc electronics
Tx amplifier
d
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MANET vs WSN Differences

• Low density vs. high density
• Address centric (IP) vs. content centric (no IP)
• Resource (constraint vs critical)
• Mobile vs stationary
• First criterion of performance (QoS vs. Power)

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Outline

• General Comments
• Wireless Sensor Network Applications
• Architecture of WSN
• Overview of Sensor Hardware
• Characteristic of WSN
• Hot Issues
• OUR WORK

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Communication Protocols
A sensor field

• MAC Protocol
• Fairness vs. Energy
• Routing Protocol
• Energy-aware routing
• Geo-routing
• Transport Control Protocol
• Congestion Control
• Reliability
• End-to-end vs. Hop-by-hop

Event
Sensor sources
Sensor sink
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Coverage Control
Communicating radius

• Problem
• Given a set of sensors deployed in a target area,
  we want to determine if the area is sufficiently
  k-covered, in the sense that every point in the
  target area is covered by at least k sensors,
  where k is a predefined constant.
• Two Motivations
• One of the measurements of the QoS
• Energy efficient
• Two conflicting objectives
• minimizing the number of active sensors to
  minimize the energy consumption.
• maintaining the coverage.
• Two metrics
• Connectivity and Coverage

Sensing radius
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Data and Query Dissemination

• Problem
• The sensor network is a distributed database.
• How to collect or query the interested data
  detected by some nodes in a energy-efficient way?
• Application-specific
• Area-based
• Attribute-based
• Pull vs. Push

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Outline

• General Comments
• Wireless Sensor Network Applications
• Architecture of WSN
• Overview of Sensor Hardware
• Characteristic of WSN
• Hot Issues
• OUR WORK

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802.11b/g
Zigbee
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Geographic Routing for Sensor Networks
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Motivation

• A sensor net consists of hundreds or thousands of
  nodes
• Scalability is the issue
• Existing ad hoc net protocols, e.g., DSR, AODV,
  ZRP, require nodes to cache e2e route information
• Dynamic topology changes
• Mobility
• Reduce caching overhead
• Hierarchical routing is usually based on well
  defined, rarely changing administrative
  boundaries
• Geographic routing
• Use location for routing
• Assumptions
• Every node knows its location
• Positioning devices like GPS
• Localization
• A source can get the location of the destination

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Geographic Routing Greedy Routing
S
D

• Find neighbors who are the closer to the
  destination
• Forward the packet to the neighbor closest to
  the destination

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Greedy Forwarding does NOT always work
GF fails

• If the network is dense enough that each
  interior node has a neighbor in every 2?/3
  angular sector, GF will always succeed

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Dealing with Void

• Apply the right-hand rule to traverse the edges
  of a void
• Pick the next anticlockwise edge
• Traditionally used to get out of a maze

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Impact of Sensing Coverage on Greedy Geographic
Routing Algorithms
Guoliang Xing, Chenyang Lu, Robert Pless,
Qingfeng Huang
IEEE Trans. Parallel Distributed System
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Theorem.

• Definition A network is sensing-covered if any
  point in the deployment region of the network is
  covered by at least one node.

Rc / Rs gt 2

• In a sensing-covered network, GF can always find
  a routing path between any two nodes.
  Furthermore, in each step (other than the last
  step arriving at the destination), a node can
  always find a next-hop node that is more than
  Rc-2Rs closer (in terms of both Euclidean and
  projected distance) to the destination than
  itself.

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GF always finds a next-hop node

• Since Rc gtgt 2Rs, point a must be outside of the
  sensing circle of si.
• Since a is covered, there must be at least one
  node, say w, inside the circle C(a, Rs).

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Theorem

• In a sensing-covered network, GF can always find
  a routing path between source u and destination v
  no longer than hops.