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Wireless Sensor Networks


Wireless Sensor Networks WSN Telecommunication EE-400 Presented By: Abdullah AL-Tuwairgi Mohammad Al-Saleh Outline Introduction-Definition A wireless sensor ... – PowerPoint PPT presentation

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Title: Wireless Sensor Networks

Wireless Sensor Networks WSN
  • Telecommunication
  • EE-400

Presented By Abdullah AL-Tuwairgi Mohammad
  • Introduction
  • Sensor network topology
  • Applications
  • Generic Node Architecture
  • Constraints for Sensor Nodes
  • Hardware Overview
  • Protocols Stack
  • Conclusion

Sensor ? measures a physical phenomenon
(motion, heat, light ) and converts it into
an electrical signal.
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

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

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

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.

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.

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

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

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

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.

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

Physical Layer (1/3)
  • Responsible of
  • Frequency selection 916 MHz, 2.4 GHz
  • carrier frequency generation,
  • signal detection,
  • modulation and data encryption.

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.

Physical Layer (3/3)-Modulation Scheme
  • M-ary scheme ? increased radio power consumption.
  • Binary modulation scheme is more energy efficient
    ?BFSK used.

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

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.

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.

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

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.

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
  • Once transmission starts, it does not stop until

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

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
Data Link Layer/S-MAC
  • Collision avoidance
  • Perform virtual and physical carrier sense before
  • 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

Data Link Layer/S-MAC
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.

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.

Network Layer (3/6)
  • Protocols Used
  • Flooding
  • SPIN
  • Directed Diffusion

Network Layer (4/6)
  • Flooding is an old technique for routing.
  • Duplicate messages.
  • Overlap.
  • Resource blindness.
  • Sensor Protocols for Information via Negotiations
  • Send sensor data instead of all the data.
  • 3 types of messages Advertise, Request Data.

Network Layer (5/6)
  • The Directed diffusion
  • Sink send out interest.
  • Each S-node stores the interest entry in its
  • 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
  • Based on data-centric routing.

Network Layer (6/6) (Low-Energy Adaptive
Clustering Hierarchy) LEACH
  • The characteristics of LEACH
  • Randomly rotating the cluster-head among
  • Low energy consumption.

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)

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

  • 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.

Thank You
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