WIRELESS SENSOR NETWORKS

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WIRELESS SENSOR NETWORKS

• BY
• VENKAT KANCHERLA
• VIJAY CHAND UYYURU

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Introduction

• A sensor network consists of a large number
  densely populated sensors acting as nodes in the
  network.
• 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.
• Sensor data is shared between the sensors and
  used as input to a distributed estimation system
  which aims to extract as much relevant
  information from the available sensor data
• The fundamental objectives for sensor networks
  are reliability, accuracy, flexibility, cost
  effectiveness and ease of deployment.

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Introduction (contd)

• A sensor network is made up of individual
  multifunctional sensor nodes
• The sensor node itself may be composed of various
  elements such as various multi-mode sensing
  hardware (acoustic, seismic, infrared, magnetic,
  chemical, imagers, microradars), embedded
  processor, memory, power-supply, communications
  device (wireless and/or wired) and location
  determination capabilities (through local or
  global techniques).

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Wireless sensor network devicedesigned to be
the approximate size of a quarter.
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Adhoc networks

• Ad hoc networks are a new paradigm of wireless
  communication for mobile hosts (which we call
  nodes).
• In an ad hoc network, there is no fixed
  infrastructure such as base stations or mobile
  switching centers.
• Mobile nodes that are within each others radio
  range communicate directly via wireless links,
  while those that are far apart rely on other
  nodes to relay messages as routers. Node mobility
  in an ad hoc network causes frequent changes of
  the network topology.
• Figure 1 shows such an example initially, nodes
  A and D have a
• direct link between them. When D moves out
  of As radio range, the link is broken. However,
  the network is still connected, because A can
  reach D through C, E, and F.

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Figure1
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Sensor networks VS ad hoc networks

• The number of nodes in a sensor network can be
  several orders of magnitude higher than the 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
• Sensor nodes mainly use broadcast, most ad hoc
  networks are based on p2p.
• Sensor nodes are limited in power, computational
  capacities and memory.
• Sensor nodes may not have global ID.

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Wireless sensor have many application areas
including

• Military,
• Environmental,
• Health,
• Home,
• Disaster relief, 
• Space exploration,
• Chemical processing,
• Other commercial

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Military Applications

• An integrated part of C4ISRT (command, control,
  communications, computer, surveillance,
  reconnaissance, targeting) systems
• Enhanced logistics systems to monitor friendly
  forces, equipment and ammunition.
• Enhanced surveillance systems to detect
  intruders, chemical or biological attacks,
  underwater targets, firing guns and their
  locations.
• Enhanced reconnaissance systems that can run in
  inaccessible or contaminated terrains and beyond
  the enemy lines.
• Enhanced targeting and target tracking systems.
• Battle damage assessment systems.
• Enhanced guidance and navigation systems.

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Civilian Applications

• Habitat monitoring.
• Environmental monitoring.
• Patient and elderly monitoring.
• Flood and forest fire detection.
• Disaster relief operations management.
• Traffic management.
• Smart office, home and car systems.
• Space exploration.
• Collaborative systems.

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Health applications

• Telemonitoring of human physiological data
• Tracking and monitoring patients and doctors
  inside a hospital
• Drug administration in hospitals

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Factors influencing sensor network design

• Fault tolerance
• Some sensor nodes may fail or be blocked due to
  lack of power, or have physical damage or
  environmental interference. The failure of sensor
  nodes should not affect the overall task of the
  sensor network. This is the reliability or fault
  tolerance issue.
• Fault tolerance is the ability to sustain sensor
  network functionalities without any interruption
  due to sensor node failures.
• The reliability Rk(t) or fault tolerance of a
  sensor node is modeled in using the Poisson
  distribution to capture the probability of not
  having a failure within the time interval (0,t)
• Rk(t) e ?k t
• where ?k is the failure rate of sensor node
  k and t is the time period.

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Factors influencing sensor network design

• Production costs
• The cost of a single node is very important to
  justify the overall cost of the networks.
• The cost of a sensor node is a very challenging
  issue given the amount of functionalities with a
  price of much less than a dollar.

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Factors influencing sensor network design

• Scalability
• The number of sensor nodes deployed in studying a
  phenomenon may be on the order of hundreds or
  thousands.
• Some times depending on the application we may
  increase the number of nodes, New schemes must be
  able to work with this number of nodes. They must
  also utilize the high density of the sensor
  networks.
• Scalability measures the density of the sensor
  nodes.
• Density µ(R) (N p R2)/A
• where N is the number of scattered sensor
  nodes in region A, and R is the radio
  transmission range. Basically, µ(R) gives the
  number of nodes within the transmission radius of
  each node in
• region A.

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Factors influencing sensor network design

• Hardware constraints

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Hardware components

• A sensor node is made up of four basic
  components, a sensing unit, a processing unit, a
  transceiver unit, and a power unit.
• additional application-dependent components such
  as a location finding system, power generator,
  and mobilizer.
• sensors and analog-to-digital converters (ADCs)
  The analog signals produced by the sensors based
  on the observed phenomenon are converted to
  digital signals by the ADC, and
• then fed into the processing unit.
• The processing unit, which is generally
  associated with a small
• storage unit, manages the procedures that
  make the sensor node collaborate with the other
  nodes to carry out the assigned sensing tasks.

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Hardware components

• A transceiver unit connects the node to the
  network.
• Power units may be supported by power scavenging
  units such as solar cells.
• Most of the sensor network routing techniques and
  sensing tasks require knowledge of location with
  high accuracy. Thus, it is common that a sensor
  node has a location finding system.
• A mobilizer may sometimes be needed to move
  sensor nodes when it is required to carry out the
  assigned tasks.

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Hardware constraints

• All of these subunits may need to fit into a
  matchbox-sized module.
• These nodes must consume extremely low power.
• Operate in high volumetric densities have low
  production cost, be dispensable and autonomous,
  operate unattended, and be adaptive to the
  environment.

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Factors influencing sensor network design

• Sensor network topology
• Deploying a high number of nodes densely requires
  careful handling of topology maintenance
• Pre-deployment and deployment phase Sensor
  nodes can be either thrown in as a mass or placed
  one by one in the sensor field. They can be
  deployed by dropping from a plane, delivered in
  an artillery shell, rocket, or missile, and
  placed one by one by either a human or a robot.
• Post-deployment phase After deployment,
  topology changes are due to change in sensor
  nodes position, reachability (due to jamming,
  noise, moving obstacles, etc.), available energy,
  malfunctioning, and task details.
• Re-deployment of additional nodes phase
  Additional sensor nodes can be redeployed at any
  time to replace malfunctioning nodes or due to
  changes in task dynamics.

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Factors influencing sensor network design

• Environment
• Sensor nodes are densely deployed either very
  close or directly inside the phenomenon to be
  observed. They usually work unattended in remote
  geographic areas
• Interior of a large machinery
• Bottom of an ocean
• Inside a twister
• Surface of an ocean during a tornado
• Biologically or chemically contaminated field
• Battlefield beyond the enemy lines
• Home or a large building
• Large warehouse
• Fast moving vehicles
• Drain or river moving with current.

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Factors influencing sensor network design

• Transmission media
• In a multihop sensor network, communicating
  nodes are linked by a wireless medium. To enable
  global operation, the chosen transmission medium
  must be available worldwide.
• Radio The Wireless Integrated Network Sensors
  (WINS) architecture uses radio links for
  communication.
• infrared Infrared communication is license-free
  and robust to interference from electrical
  devices. Infrared-based transceivers are cheaper
  and easier to build
• optical media Another interesting development
  is that of the Smart Dust mote, which is an
  autonomous sensing, computing, and communication
  system that uses the optical medium for
  transmission.

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Factors influencing sensor network design

• Power consumption
• The wireless sensor node, being a microelectronic
  device, can only be equipped with a limited power
  source (lt 0.5 Ah, 1.2 V)
• In a multihop ad hoc sensor network, each node
  plays the dual role of data originator and data
  router.
• 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 hence be divided into three
  domains
• Sensing
• Communication
• Data processing

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Environmental monitoring

• Redwood trees are so large that entire ecosystems
  exist within their physical envelope.
• Climatic factors determine the rate of
  photosynthesis, water and nutrient transport, and
  growth patterns.
• microclimatic structure varies over regions of
  the forest.
• water transport rates and the scale of
  respiration may influence the microclimate around
  a tree, effectively creating its own weather
• All these factors influence the habitat dynamics
  of species existing in and on the tree.

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Wireless sensor node for environment monitoring
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Wireless sensor node for environment monitoring

• On top, two incident-light sensors measure total
  solar radiation, specifically light and
  photosynthetically active radiation, the bands at
  which chlorophyll are sensitive.
• An identical pair of sensors on the bottom, to
  monitor relative humidity, barometric pressure,
  and temperature
• Contains a small computer, data storage, battery,
  and
• low-power radio to collect data, process it,
  and route information among the nodes and to the
  outside world

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WSN climate data
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Results

• The measurements show that within the expected
  daily cycle, the top of the tree experiences much
  wider climatic variation than the forest floor.
• These weather fronts create powerful temperature
  and moisture gradients that could be instrumental
  in understanding growth dynamics, water intake,
  and nutrient transport over such large
  structures, yet they cannot be observed with
  sparse instrumentation.

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Communication architecture of sensor networks

• The sensor nodes are usually scattered in a
  sensor field as shown below

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Sensor communication

• Each of these scattered sensor nodes has the
  capabilities to collect data and route data back
  to the sink.
• Data are routed back to the sink by a multi-hop
  infra-structure less architecture through the
  sink.
• The sink may communicate with the task manager
  node via Internet or satellite.
• The design of the sensor network is influenced by
  many factors, including fault tolerance,
  scalability, production costs, operating
  environment, sensor network topology, hardware
  constraints, transmission media, and power
  consumption.

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Data in sensor networks

• Sensor networks are predominantly data-centric
  rather than address-centric.
• Given the similarity in the data obtained by
  sensors in a dense cluster, aggregation of the
  data is performed locally. Summary or analysis is
  done by aggregator node to reduce the bandwidth
  requirement.
• A network hierarchy and clustering of sensor
  nodes allows for network scalability, robustness,
  efficient resource utilization and lower power
  consumption.

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Data in sensor networks (contd..)

• Dissemination of sensor data in an efficient
  manner requires the dedicated routing protocols
  to identify shortest paths.
• Redundancy must be accounted for to avoid
  congestion resulting from different nodes sending
  and receiving the same information.
• We need redundancy to ensure reliability.
• Data dissemination may be either query driven or
  based on continuous updates.
• The operation of a sensor network includes a
  variety of information processing techniques for
  the manipulation and analysis of sensor data,
  extraction of significant features, along with
  the efficient storage and transmission of the
  important information.

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Communication architecture of sensor networks

• The protocol stack used by sink and all sensor
  nodes is as shown below

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Communication architecture of sensor networks

• Application layer
• An application layer management protocol
  makes the hardware and software of the lower
  layers transparent to the sensor network
  management applications.
• Sensor management protocol (SMP)
• Task assignment and data advertisement protocol
  (TADAP)
• Sensor query and data dissemination protocol
  (SQDDP)

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Communication architecture of sensor networks

• Transport layer
• This layer is especially needed when the system
  is planned to be accessed through Internet or
  other external networks.
• No attempt thus far to propose a scheme or to
  discuss the issues related to the transport layer
  of a sensor network in literature.
• The communication between user and sink is
  TCP/UDP via the Internet or Satellite.
• The communication between the sink and sensor
  nodes may be purely by UDP protocols.

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Communication architecture of sensor networks

• Network layer
• Power efficiency is always an important
  consideration.
• Sensor networks are mostly data centric.
• Data aggregation is useful only when it does not
  hinder the collaborative effort of the sensor
  nodes.
• An ideal sensor network has attribute-based
  addressing and location awareness.

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Communication architecture of sensor networks

• Maximum available power (PA) route
• Minimum energy (ME) route
• Minimum hop (MH) route
• Maximum minimum PA node route

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Communication architecture of sensor networks

• Maximum available power (PA) route The route
  that has maximum total available power is
  preferred. (route 4)
• Minimum energy (ME) route The route that
  consumes ME to transmit the data packets between
  the sink and the sensor node is the ME route.
  (route 1)
• Minimum hop (MH) route The route that makes the
  MH to reach the sink is preferred. (route 3)
• Maximum minimum PA node route The route along
  which the minimum PA of the other routes is
  preferred. (route 3)

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Communication architecture of sensor networks

• Data Aggregation It can be perceived as a set of
  automated methods of combining the data that
  comes from many sensor nodes into a set of
  meaningful information. It is also known as Data
  Fusion.
• It is a technique used to solve the implosion and
  overlap problems in data-centric routing.
• In this technique, a sensor network is usually
  perceived as a reverse multicast tree as shown in
  the fig. where the sink asks the sensor nodes to
  report the ambient condition of the phenomena.

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Communication architecture of sensor networks

• Data aggregation

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Communication architecture of sensor networks

• Data link layer
• The data link layer is responsible for the
  medium access and error control. It ensures
  reliable point-to-point and point-to-multipoint
  connections in a communication network.

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Communication architecture of sensor networks

• Medium access control
• Creation of the network infrastructure
• Fairly and efficiently share communication
  resources between sensor nodes

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Communication architecture of sensor networks

• Power saving modes of operation
• Operation in a power saving mode is energy
  efficient only if the time spent in that mode is
  greater than a certain threshold.

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Communication architecture of sensor networks

• Error control
• Forward Error Correction (FEC)
• Automatic Repeat Request (ARQ).
• Simple error control codes with low-complexity
  encoding and decoding might present the best
  solutions for sensor networks.

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Communication architecture of sensor networks

• Physical layer
• The physical layer is responsible for
  frequency selection, frequency generation, signal
  detection, modulation and data encryption.

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Communication architecture of sensor networks

• Power management This plane manages how a sensor
  node uses its power.
• Mobility management This plane detects and
  registers the movement of sensor nodes, so a
  route back to the user is always maintained and
  the sensor nodes can keep track of who are their
  neighbor sensor nodes.
• Task management This plane is needed, so that
  sensor network nodes can work together in a
  power efficient way , route data in a mobile
  sensor network, and share resources between
  sensor nodes.

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Conclusion

• 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.
• In the future, this wide range of application
  areas will make sensor networks an integral part
  of our lives.

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Questions?

• What are factors influencing sensor network
  design?
• What are different components of a sensor node?
• What is data aggregation?

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• THANK YOU