Wireless Sensor Networks

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Wireless Sensor Networks WSN

• Telecommunication
• EE-400

Presented By Abdullah AL-Tuwairgi Mohammad
Al-Saleh
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Outline

• Introduction
• Sensor network topology
• Applications
• Generic Node Architecture
• Constraints for Sensor Nodes
• Hardware Overview
• Protocols Stack
• Conclusion

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Introduction-Definition
Sensor ? measures a physical phenomenon
(motion, heat, light ) and converts it into
an electrical signal.
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Introduction-Definition
Wireless Sensor Networks (WSN)

• A wireless sensor network is a special network
  with large numbers of nodes.
• The nodes are equipped with embedded
  processors, sensors and radios.
• These nodes collaborate to accomplish a common
  task such as environment monitoring or asset
  tracking.

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Introduction
Smart Sensor Processor Sensors Wireless
Interface
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Ad Hoc Wireless Networks
In many applications, the nodes are deployed in
Ad Hoc fashion.
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Introduction
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Sensor network topology

• The sensor nodes are usually scattered in a
  sensor field.
• Nodes collect data and route data back to the end
  users by a multi-hop infrastructure-less
  architecture through the sink.
• The sink may communicate with the task manager
  node via Internet or Satellite.

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Applications
Smart Buildings to improve living conditions and
reduce energy consumption
Inventory Management

• Environmental monitoring
• Seismic activity detection
• Industrial monitoring and control
• High-precision agriculture
• Structural health monitoring
• healthcare and medical research
• Homeland security.
• military applications.

Fire Monitoring
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Generic Node Architecture

• A sensor node is made up of four basic
  components
• Sensing Unit. 2) Processing Unit.
• 3) Transceiver Unit 4) Power Unit.
• Additional units ? location finding system--power
  generator--mobilizer.

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Constraints for Sensor Nodes

• Required small size
• Can be placed in more locations and used in more
  scenarios (applications) ? more flexibility.
• Collect more data ? deployed densely.

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Constraints for Sensor Nodes

• Consume extremely low power (µAmps.)
• use low-power hardware components .
• Transmit and receive only if necessary.
• Power consumption in each node
• sensing, data processing and communication.
• Radio communication will consume a significant
  fraction of total energy.

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Constraints for Sensor Nodes

• Strategies to reduce the average supply current
  of the radio
• Reduce the amount of data transmitted through
  data compression and reduction.
• Reduce the frame overhead.
• Implement strict power management mechanisms
  (power-down and sleep modes).
• only transmit data when a sensor event occurs

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Constraints for Sensor Nodes

• Have low production cost.
• In some application response time is a critical
  (security system) ? quick response time is
  required.
• WSN need privacy also be able to authenticate
  data communication.
• Scalability
• Some nodes may die or new nodes may join

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Examples of nodes
Hardware Overview Node (1/2)
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Hardware Overview Node (2/2)

• (( Mica Z Mote ))
• Sensors light, temperature, pressure,
  acceleration, acoustic, magnetic
• Characteristics
• Microcontroller (ATMega128L) 7.4 MHz, 8 bit.
• Memory 4KB data, 128 KB program.
• Radio lt 40 Kbps, 2.4GHz,
• DS-SS (ZigBee).
• Special connector for Crossbow sensor boards.
• Special Operating System TinyOS.
• Power
• Alkaline/Lithium batteries.
• Lifetime of 450 days requires 1 duty cycle.

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Protocol Stack

• The protocol stack used by the sink and all
  sensor nodes
• Combines power and routing awareness,
• integrates data with networking protocols,
• communicates power efficiently through the
  wireless medium.
• promotes cooperative efforts of nodes.

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Protocol Stack

• The power, mobility, and task management planes
  monitor the power, mobility, and task
  distribution among the sensor nodes.

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Physical Layer (1/3)

• Responsible of
• Frequency selection 916 MHz, 2.4 GHz
• carrier frequency generation,
• signal detection,
• modulation and data encryption.

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Physical Layer (2/3)-Propagation Aspects

• Energy minimization has significant importance
  more than
• scattering, shadowing, reflection, diffraction,
  multi-path and fading effects.
• Multi-hop communication can effectively overcome
  shadowing and path-loss effects, if the node
  density is high enough.

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Physical Layer (3/3)-Modulation Scheme

• M-ary scheme ? increased radio power consumption.
  
• Binary modulation scheme is more energy efficient
  ?BFSK used.

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Data Link Layer

• Responsible for
• the multiplexing of data streams,
• data frame detection,
• medium access and error control.

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Data Link Layer-MAC Protocol

• Sources of energy inefficiency
• Collision.
• Overhearing.
• Control packet overhead.
• Idle listening.
• ? So, there is a need for a MAC protocol that
  solve these problems.

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Data Link Layer-MAC Protocol

• Several Protocols used in the Link Layer
• Self-Organizing Medium Access Control for Sensor
  Networks (S-MACS)
• CSMA.
• Hybrid TDMA/FDMA based.

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Data Link Layer/S-MAC

• S-MAC
• MAC protocol specifically designed for WSN.
• Building on random access - based protocols.
• S-MAC solve the problem of all the major sources
  of energy waste
• idle listening, collision, overhearing and
  control overhead.
• Not suitable for time-critical applications ?
  because latency in end-to-end communication.
• Design goals
• Reduce energy consumption
• Support good scalability
• Self-configurable

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Data Link Layer/S-MAC

• Uses a sleep/wakeup cycle to allow nodes to spend
  most of their time sleep
• Listen period
• for nodes that have data to send to coordinate.
• A sleep period
• nodes sleep if they have no data to send or
  receive, and nodes remain awake and exchange data
  if they are involved in communication.
• In a sleep mode when the radio is switched off,
  the node sets a timer to awake later.
• When the timer expires, it wakes up.
• Selection of sleep and listen duration is based
  on the application scenarios.

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Data Link Layer/S-MAC

• Each node maintains a schedule table.
• Nodes exchange schedules by broadcast.
• Multiple neighbors contend for the medium
• A communication link
• a pair of time slots operating at a randomly
  chosen but fixed frequency (or frequency hopping
  sequence).
• Once transmission starts, it does not stop until
  completed.

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Data Link Layer/S-MAC

• Nodes a and b follow different schedules.
• If a wants to send to b, it just wait until b is
  listening.

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Data Link Layer/S-MAC

• Neighboring nodes are synchronized together.
• Maintaining Synchronization
• Needed to prevent clock drift
• Periodic updating using a SYNC packet
• Receivers adjust their timer counters

Sender Node ID
Next-Sleep Time
SYNC Packet
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Data Link Layer/S-MAC

• Collision avoidance
• Perform virtual and physical carrier sense before
  transmission.
• RTS/CTS solves the hidden terminal problem.
• Interfering nodes go to sleep after they hear the
  RTS or CTS packet
• Overhearing Avoidance
• NAV. indicates how long the remaining
  transmission will be.
• The medium is busy when the NAV value is not zero
  
• All immediate neighbors of sender and receiver
  should go to sleep ? avoiding energy waste on
  overhearing.

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Data Link Layer/S-MAC
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Network Layer (1/6)

• Special multi-hop wireless routing protocols
  between sink node and sensors are needed.
• Traditional ad hoc routing techniques do not
  usually fit.
• When we design network layer protocols for sensor
  networks, we need to consider
• Power efficiency.
• Sensor networks are data-centric.
• addressing and location awareness.

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Network Layer (2/6)

• Routing Techniques
• Maximum PA route
• Max. total PA without including routes that
• add extra hops.
• Minimum Energy route
• Route that consumes min. energy.
• Energy-efficient routes
• can be found based on the available
• power (PA) and the energy required a
• for transmission in the links.
• Minimum hop route
• Min. hop to reach the sink.
• Maximum minimum PA node route
• Use the route in which the min. PA is larger
• than the min. PAs of the other routes.
• This scheme prevents the risk of using up a
  sensor node with low PA much earlier than the
  others just because it is on the route with nodes
  that have very high PAs.

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Network Layer (3/6)

• Protocols Used
• Flooding
• SPIN
• Directed Diffusion
• LEACH

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Network Layer (4/6)

• Flooding is an old technique for routing.
• Duplicate messages.
• Overlap.
• Resource blindness.
• Sensor Protocols for Information via Negotiations
  (SPIN)
• Send sensor data instead of all the data.
• 3 types of messages Advertise, Request Data.

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Network Layer (5/6)

• The Directed diffusion
• Sink send out interest.
• Each S-node stores the interest entry in its
  cache.
• Interest entry contains a timestamp and several
  gradient fields.
• As the interest propagates, the gradients back to
  sink are set up.
• When the source has data for the interest, the
  source sends data along the interests gradient
  path.
• Based on data-centric routing.

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Network Layer (6/6) (Low-Energy Adaptive
Clustering Hierarchy) LEACH

• The characteristics of LEACH
• Randomly rotating the cluster-head among
  sensors.
• Low energy consumption.

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Transport Layer

• Transport layer is especially needed when the
  system is planned to be accessed through the
  Internet or other external networks.
• TCP transmission window mechanisms is not
  suitable, TCP splitting will be used
• Between User Sink (TCP or UDP)
• Between Sink nodes (UDP)

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Application Layer

• Sensor Management protocol
• Exchanging the data.
• Time synchronization
• Moving the nodes, turning them on and off etc.
• Sensor Query and Data distribution protocol.
• User applications with interfaces to issue
  queries, respond to queries and collect incoming
  replies.

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Conclusion

• The Protocols used are not well defined and they
  are open research issues.
• The advantages of WSNs create many new and
  exciting application areas for remote sensing, so
  they will be an integral part of our lives.

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Thank You