Wireless Sensor Networks

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Wireless Sensor Networks

• Presenter Xiaodong Zhou
• Thayer School of Engineering
• Dartmouth College
• Hanover,NH,03755

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Outline

• 1. Introduction
• 2. Sensor networks applications
  (Military,Environmental,Health,Home,other
  commercial applications)
• 3.Factors influencing sensor network design
• (fault tolerance,scalability,production
  cost,hardware constraints,environment,transmission
  media,power consumption)
• 4.Sensor networks communication architecture
  (application,transport,network,data link,physical
  layers)
• 5.Conclusion

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Introduction

• A sensor network is composed of a large number of
  sensor nodes, which are densely deployed either
  inside the phenomenon or very close to it.
• Applications
• Military applications
• Environmental applications
• Health applications
• Home applications
• Other commercial applications
  

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Factors influencing sensor network design (1)

• Fault tolerance
• Fault tolerance is the ability to sustain sensor
  network functionalities without any interruption
  due to sensor node failures.
• Protocols and algorithms may be designed to
  address the level of fault tolerance required by
  the Sensor Networks.
• Little interference the protocols can be more
  relaxed (home application)
• High interference the fault tolerance has to be
  high (battlefield)

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Factors influencing sensor network design (2)

• Scalability
• The ability to work with large number of sensor
  nodes, and to utilize the high density nature of
  the sensor networks.
• Production Cost
• Blue-tooth radio system lt10
• Pico Node lt1 (target price)
• Sensor node ltlt1 (target price) (sensing and
  processing unit, location finding sys, mobilizer,
  power generator)
• very challenging issue given the amount of the
  functionalities with a price much less than 1

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Factors influencing sensor network design (3)

• Hardware constraints
• Four basic components
• sensing unit, processing unit, transceiver
  unit, power unit
• Application dependent additional component
• location finding sys, power generator,
  mobilizer
• Stringent constraints for sensor nodes
• (1) Matchbox-size module, maybe smaller that 1cm3
  
• (2) Consume extremely low power
• (3) Operate in high volumetric densities
• (4) Have low production cost and be dispensable
• (5) Be autonomous and operate unattended
• (6) Be adaptive to the environment

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Factors influencing sensor network design (4)

• Sensor network topology
• 1. Pre-deployment and deployment phase
• thrown in mass or placed one by one in the
  sensor filed, the schemes for initial deployment
  must
• a. reduce the installation cost
• b. eliminate the need for any
  pre-organization and pre-planning
• c. increase the flexibility of arrangement
• d. promote self-organization and fault
  tolerance
• 2. Post deployment phase
• The sensor nodes may be statically deployed.
• Topology changes are due to change in sensor
  nodes position, reachability, available energy,
  malfunctioning and task details.
• 3. Re-deployment of additional nodes phase
• Additional nodes can be re-deployed to
  replace the malfunctioning nodes.
• Need to re-organize the network

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Factors influencing sensor network design (5)

• Environment
• Conditions sensor nodes are expected to work
  under
• In busy intersections
• In the interior of a large machinery
• At the bottom of the ocean
• Inside a twister
• In a biologically or chemically contaminated
  field
• In the battlefield beyond enemy lines
• In a home or large building
• Attached to animals
• Attached to fast moving vehicles
• In a drain or river moving with current

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Factors influencing sensor network design (6)

• Wireless transmission media
• Radio, infrared or optical media (must be
  available worldwide)
• (1) Industrial scientific and medical band (ISM)
• Advantage free radio, huge spectrum allocation
  and global availability, and not bound to a
  particular standard, giving more freedom for the
  implementation of power saving strategies in
  sensor networks
• (2) Infrared communication
• Advantage License-free and robust to
  interference from electrical devices. They are
  cheaper and easier to build
• Drawback require a line of sight between sender
  and receiver.
• (3) Optical medium (two transmission schemes)
• Passive communication corner-cube
  retroreflector (CCR)
• Active communication laser diode and steerable
  mirrors

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Factors influencing sensor network design (7)

• Power consumption
• Limited power source (lt0.5Ah, 1.2 V)
• In a multihop ad hoc sensor network, each nodes
  plays a dual role of data originator and data
  router. The disfunctioning of few nodes can cause
  significant topological changes and might require
  re-routing of packets and re-organization of the
  network.
• So the consideration of the power conservation
  and power management is of importance.
• Since the main task of a sensor node in a sensor
  field is to detect events, perform quick local
  data processing and then transmit the data, Power
  consumption can be divided into 3 domains(
  sensing, communication and data processing)

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Factors influencing sensor network design (8)

• Sensing
• Since the sensor nodes are often inaccessible,
  the lifetime of a sensor network depends on the
  lifetime of the power resources of the nodes.
• Smart dust mote on the order of 1J
• Wireless integrated network sensors (WINS) 30µA
  , lithium coin cells
• Need to consider extend the lifetime of the
  sensor networks by energy scavenging, which means
  extracting energy from the environment. Solar
  cells.

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Factors influencing sensor network design (9)

• Communication (Data transmission and reception)
• Have maximum energy usage
• Mixer, frequency synthesizers, voltage control
  oscillators, phase locked loops (PLL) and power
  amplifiers all consume valuable power
• Active power consumption, start-up power
  consumption
• Insufficient in turning the transceiver ON and
  OFF, cause a large amount of power is spent in
  turning the transceiver back ON each time.

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Sensor network communication architecture
The sensor nodes are usually scattered in a
sensor field. Each of these scattered sensor
nodes has the capabilities to collect data and
route data back to the sink and the end users.
Data are routed back to the end user by a
multihop infrastructureless architecture through
the sink . The sink may communicate with the task
manager node via internet or satellite
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• The protocol stack used by the sink and all
  sensor nodes combines power and routing
  awareness, integrates data with network
  protocols, communicates power efficiently through
  the wireless medium, and promotes cooperative
  efforts of sensor nodes.

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• Application Layer ( 3 possible application layer
  protocols)
• 1. Sensor Management Protocol (SMP)
• SMP is a management protocol that provides the
  software operations needed to perform the
  following administrative tasks
• (1) Introducing the rules related to data
  aggregation, attribute-based naming and
  clustering to the sensor nodes
• (2) Exchange data related to the location finding
  algorithms
• (3) Time synchronization of the sensor nodes
• (4) Moving sensor nodes
• (5) Turning sensor nodes on and off
• (6) Querying the sensor network configuration and
  the status of nodes, and re-configuring the
  sensor network
• (7) Authentication, key distribution and security
  in data communication

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• Application Layer ( 3 possible application layer
  protocols)
• 2. Task assignment and data advertisement
  protocol (TADAP)
• Interest dissemination is another important
  operation in the sensor network
• Users send their interest to a sensor node, this
  interest may be about a certain attribute of the
  phenomenon or a triggering event.
• An application layer protocol that provides the
  users software with efficient interfaces for
  interest dissemination is useful for lower layer
  operations.

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• Application Layer ( 3 possible application layer
  protocols)
• 3. Sensor query and data dissemination protocol
  (SQDDP)
• SQDDP provides user applications with interfaces
  to issue queries, respond to queries and collect
  incoming replies.
• These queries are generally not issued to
  particular nodes, instead attribute-based or
  location-based naming is preferred.

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• Transport layer
• This layer is especially needed when the system
  is planned to be accessed through internet or
  other external networks.
• TCP splitting
• TCP connections are ended at sink nodes, and a
  special transport layer protocol can handle the
  communications between sink node and the sensor
  nodes. As a result, the communication between the
  user and the sink node is by UDP or TCP via the
  internet or satellite on the other hand, the
  communication between the sink and sensor nodes
  may be purely by UDP type protocols, because each
  node has limited memory.

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• Network layer
• The networking layer of sensor networks is
  usually designed according to the following
  principles
• 1. Power efficiency
• 2. Sensor networks are mostly data centric
• 3. Data aggregation is useful only when it does
  not hinder the collaborative effort of the sensor
  nodes
• 4. An ideal sensor network has attribute-based
  addressing and location awareness
• Energy efficient route finding
• Maximum available power (PA) route
• Minimum energy (ME) route
• Minimum hop (MH) route
• Maximum minimum PA node route

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• Maximum available power (PA) route
• The route that has maximum total available power
  is preferred. The total PA is calculated by
  summing the PAs of each node along the route.
  (route 2)
• Minimum energy (ME) route
• The route that consumes ME to transmit the data
  packets between the sink and the sensor node.
  (route 1)
• Minimum hop (MH) route
• The route that makes the MH to reach the sink .
  (route 3)
• Maximum minimum PA node route
• The route along which the minimum PA is larger
  than the minimum PAs of the other routes. (route
  3)

Route 1 sink-A-B-T PA4, a3 Route 2
sink-A-B-C-T PA6, a6 Route 3 sink-D-T PA3
a4 Route 4 sink-E-F-T PA5, a 6 PA
available power a energy required to transmit a
data packet through the related link
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Current research on network layer 1. Small
minimum energy communication network (SMECN)
V. Rodoplu, etc, Minimum energy mobile wireless
networks, IEEE Journal of selected areas in
communications 17(8) 1999 ,1333-1334 2. Flooding
W.R.Heinzelman, etc, Adaptive protocols for
information dissemination in wireless sensor
networks, proceeding of ACM MobiCom99, Seattle,
Washington, 1999, 174-185 3. Gossiping S.
Hedetniemi, etc, A survey of gossiping and
broadcasting in communication networks, networks
18 (4) 1998, 319-349 4. Sensor protocols for
information via negotiation (SPIN)
W.R.Heinzelman, etc, Adaptive protocols for
information dissemination in wireless sensor
networks, proceeding of ACM MobiCom99, Seattle,
Washington, 1999, 174-185 5. Sequential
assignment routing (SAR) K.Sohrabi, etc,
Protocols for self-organization of a wireless
sensor network, IEEE Personal Communications,
2000, 16-27
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Current research on network layer
(continued) 6. Low-energy adaptive clustering
hierarchy (LEACH) W.R.Heinzelman, etc,
Energy-efficient communication protocol for
wireless micro sensor networks, IEEE proceeding
of the Hawaii international conference on system
sciences, 2000, 1-10 7. Direct diffusion
C.Intanagonwiwat, Directed diffusion a scalable
and robust communication paradigm for sensor
networks, proceeding of ACM Mobil00, Boston,
2000, 56-67
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An overview of network layer schemes
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• Data link layer
• Data link layer is responsible for the
  multiplexing of data streams, data frame
  detection, medium access and error control.
• 1. Medium access control
• Two goals of MAC protocol in a wireless
  multihop self-organizing sensor network
• A. the creation of the network infrastructure
• B. fairly and efficiently share communication
  resources between sensor nodes
• The MAC protocol for sensor networks must
  have built-in power conservation, mobility
  management and failure recovery strategies.
• Some of the proposed MAC protocols
• SMACS and the EAR algorithm
• CSMA based medium access
• Hybrid TDMA/FDMA based

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An overview of MAC protocols for sensor networks
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• Data link layer
• 2. Power saving modes of operation
• Regardless of which type of medium access scheme
  is used for sensor networks, it certainly must
  support the operation of power saving modes for
  the sensor node.
• Dynamic power management in wireless sensor
  networks IEEE Design and test of Computers,
  2001, by A.Sinha, etc
• A dynamic power management scheme for wireless
  sensor network is discussed. And five power
  saving modes are proposed and intermode
  transition policies are investigated.

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• Data link layer
• 3. Error control
• The error control of transmission data is another
  important function of data link layer.
• Two important modes of error control in
  communication network are
• Forward error correction (FEC)
• Automatic repeat request (ARQ)
• But they are unexplored in the regime of sensor
  networks.
• The feasibility of other error schemes in sensor
  networks needs to be explored.

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• Physical layer
• The physical layer is responsible for frequency
  selection, carrier frequency generation, signal
  detection, modulation and data encryption.
• What are the problems while designing the
  physical layer for sensor networks?
• energy minimization, decay, scattering ,
  shadowing, reflection, diffraction, multipath and
  fading effects
• Although some of these topics have been addressed
  in the literature, it still remains a vastly
  unexplored domain of the wireless sensor
  networks.

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Conclusions

• The flexibility, fault tolerance, high sensing
  fidelity, low cost and rapid deployment
  characteristics of sensor networks create many
  new and exciting application areas for remote
  sensing.
• However, realization of sensor networks needs to
  satisfy the constraints introduced by factors
  such as fault tolerance, scalability, cost,
  hardware, topology change, environment and power
  consumption.
• New wireless ad hoc networking techniques are
  required..

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• Current sensor network research projects

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Questions?????