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Wireless Sensor Networks

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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


1
Wireless Sensor Networks WSN
  • Telecommunication
  • EE-400

Presented By Abdullah AL-Tuwairgi Mohammad
Al-Saleh
2
Outline
  • Introduction
  • Sensor network topology
  • Applications
  • Generic Node Architecture
  • Constraints for Sensor Nodes
  • Hardware Overview
  • Protocols Stack
  • Conclusion

3
Introduction-Definition
Sensor ? measures a physical phenomenon
(motion, heat, light ) and converts it into
an electrical signal.
4
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.

5
Introduction
Smart Sensor Processor Sensors Wireless
Interface
6
Ad Hoc Wireless Networks
In many applications, the nodes are deployed in
Ad Hoc fashion.
7
Introduction
8
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.

9
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
10
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.

11
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.

12
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.

13
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

14
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

15
Examples of nodes
Hardware Overview Node (1/2)
16
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.

17
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.

18
Protocol Stack
  • The power, mobility, and task management planes
    monitor the power, mobility, and task
    distribution among the sensor nodes.

19
Physical Layer (1/3)
  • Responsible of
  • Frequency selection 916 MHz, 2.4 GHz
  • carrier frequency generation,
  • signal detection,
  • modulation and data encryption.

20
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.

21
Physical Layer (3/3)-Modulation Scheme
  • M-ary scheme ? increased radio power consumption.
  • Binary modulation scheme is more energy efficient
    ?BFSK used.

22
Data Link Layer
  • Responsible for
  • the multiplexing of data streams,
  • data frame detection,
  • medium access and error control.

23
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.

24
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.

25
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

26
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.

27
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.

28
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.

29
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
30
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.

31
Data Link Layer/S-MAC
32
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.

33
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.

34
Network Layer (3/6)
  • Protocols Used
  • Flooding
  • SPIN
  • Directed Diffusion
  • LEACH

35
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.

36
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.

37
Network Layer (6/6) (Low-Energy Adaptive
Clustering Hierarchy) LEACH
  • The characteristics of LEACH
  • Randomly rotating the cluster-head among
    sensors.
  • Low energy consumption.

38
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)

39
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.

40
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.

41
Thank You
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