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Introduction to Sensor Networks


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Title: Introduction to Sensor Networks

Introduction to Sensor Networks
  • Rabie A. Ramadan, PhD
  • Cairo University
  • http//
  • 1

  • Website
  • http//

Class Format
  • Presentations by myself
  • Assignments
  • Survey on one of the following topics
  • Topics
  • Survey Format

  • Some other materials will be provided

  • Introduction and Basic Concepts

Wireless Networks
  • Most of the traditional wireless networks occur
    over fixed infrastructure
  • Access points
  • Many wireless protocols (heterogeneity problem)
  • Bluetooth, WiFi, WiMax
  • We need Seamless network
  • Connects everyone from their home to work,..
  • Disasters may be a drive force for such networks

Katrina hurricane, 2006
General Types of Wireless Networks
  • Wireless Cellular Networks
  • First , Second, 2.5 , third, and 4th generations
  • Wireless Ad Hoc Networks
  • Nodes function as host and router
  • Dynamic topology
  • Nodes may departure
  • Requires efficient routing protocols
  • Mobile Ad Hoc Networks (MANET)
  • Wireless Sensor Networks (WSN)

Wireless Sensor Networks
Definitions and Background
  • Sensing
  • Is a technique used to gather information about
    a physical object or process, including the
    occurrence of events (i.e., changes in state such
    as a drop in temperature or pressure).
  • Sensor
  • An object performing such a sensing task
  • Converts energy of the physical worlds into
    electrical signal.
  • Sometimes named Transducer ? converts energy
    from one form to another.

Definitions and Background
  • Examples on remote sensors
  • eyes capture optical information (light)
  • ears capture acoustic information (sound)
  • nose captures olfactory information (smell)
  • skin captures tactile information (shape,

Sensing Task
e.g. amplification, filtering, ..etc
An example of a sensor Passive infrared
  • PIR is a differential sensor detects target as
    it crosses the beams produced by the optic

PIR signal Amplitude
Car 20-25 mph _at_ 25m
Human 3 mph _at_ 10m
What is a Smart Sensor Node?
Nodes Responsibilities
  • Data Collection
  • In-Network Analysis
  • Data Fusion
  • Decision Making

Sensors Classification
Physical property to be monitored determines type
of required sensor
Type Examples
Temperature Thermistors, thermocouples
Pressure Pressure gauges, barometers, ionization gauges
Optical Photodiodes, phototransistors, infrared sensors, CCD sensors
Acoustic Piezoelectric resonators, microphones
Mechanical Strain gauges, tactile sensors, capacitive diaphragms, piezoresistive cells
Motion, vibration Accelerometers, mass air flow sensors
Position GPS, ultrasound-based sensors, infrared-based sensors, inclinometers
Electromagnetic Hall-effect sensors, magnetometers
Chemical pH sensors, electrochemical sensors, infrared gas sensors
Humidity Capacitive and resistive sensors, hygrometers, MEMS-based humidity sensors
Radiation Ionization detectors, Geiger-Mueller counters
Other Classifications
  • Power supply
  • active sensors require external power, i.e., they
    emit energy (microwaves, light, sound) to trigger
    response or detect change in energy of
    transmitted signal (e.g., electromagnetic
    proximity sensor)
  • passive sensors detect energy in the environment
    and derive their power from this energy input
    (e.g., passive infrared sensor)
  • Electrical phenomenon
  • resistive sensors use changes in electrical
    resistivity (?) based on physical properties such
    as temperature (resistance R ?l/A)
  • capacitive sensors use changes in capacitor
    dimensions or permittivity (e) based on physical
    properties (capacitance C eA/d)
  • inductive sensors rely on the principle of
    inductance (electromagnetic force is induced by
    fluctuating current)
  • piezoelectric sensors rely on materials
    (crystals, ceramics) that generate a displacement
    of charges in response to mechanical deformation

What is a sensor Network?
Wireless Sensor Network (WSN)
  • Multiple sensors (often hundreds or thousands)
    form a network to cooperatively monitor large or
    complex physical environments
  • Acquired information is wirelessly communicated
    to a base station (BS), which propagates the
    information to remote devices for storage,
    analysis, and processing

History of WSN
History of Wireless Sensor Networks
  • Distributed Sensor Nets Workshop (1978)
  • Distributed Sensor Networks (DSN) program (early
  • Sensor Information Technology (SensIT) program
  • UCLA and Rockwell Science Center
  • Wireless Integrated Network Sensors (WINS)
  • Low Power Wireless Integrated Microsensor (LWIM)
  • UC-Berkeley
  • Smart Dust project (1999)
  • concept of motes extremely small sensor nodes
  • Berkeley Wireless Research Center (BWRC)
  • PicoRadio project (2000)
  • MIT
  • µAMPS (micro-Adaptive Multidomain Power-aware
    Sensors) (2005)

Sample Sensor Hardware Berkeley motes
(No Transcript)
Commercial Effort
  • Crossbow (,
  • Sensoria (,
  • Worldsens (http//,
  • Dust Networks (http// ),
  • Ember Corporation (http// ).

Challenges and Constraints
  • Energy
  • Sensors powered through batteries? sometimes
    impossible to do.
  • Mission time may depend on the type of
    application (e.g. battlefield monitoring hours
    or days)
  • Nodes layers must be designed carefully.

Wireless Range Controls the Network Topology
Routing in multihop network is a challenge Relay
node may aggregate the data
Medium Access Control layer (MAC)
  • Responsible for providing sensor nodes with
    access to the wireless channel.
  • Responsible of Contention free Transmission .
  • MAC protocols have to be contention free as well
    as energy efficient.
  • Contention free requires listening to the
    wireless channel all the time
  • Energy efficient requires turning off the radio

Network Layer
  • Responsible for finding routes from a sensor node
    to the base station
  • Route characteristics such as length (e.g., in
    terms of number of hops), required transmission
    power, and available energy on relay nodes
  • Determine the energy overheads of multi-hop
    communication and try to avoid it.

Operating System
  • Energy affects the O.S. design
  • Small memory footprint,
  • Efficient switching between tasks
  • security mechanisms

Challenges and Constraints
  • Self-Management
  • Sensors usually deployed in harsh environment.
  • There is no pre-infrastructure setup.
  • Once deployed, must operate without human
  • Sensor nodes must be self-managing in that
  • They configure themselves,
  • Operate and collaborate with other nodes,
  • Adapt to failures, changes in the environment,

A self-managing Network
  • Self-organization
  • A networks ability to adapt configuration
    parameters based on system and Environmental
  • Self-optimization
  • A devices ability to monitor and optimize the
    use of its own system resources
  • Self-protection
  • Allows a device to recognize and protect itself
    from intrusions and attacks
  • Self-healing
  • Allows sensor nodes to discover, identify, and
    react to network disruptions.

Ad Hoc Deployment
  • Deterministic Vs. Ad Hoc Deployment

Challenges and Constraints
  • Wireless Networking
  • Transmission Media
  • Sensors use wireless medium
  • Suffer from the same problems that wireless
    networks suffer from
  • Fading
  • High error rate

Challenges and Constraints
  • Wireless Networking
  • Communication range
  • Communication ranges are always short
  • It is required for the network to be highly
  • Routing paths will be long
  • What about critical applications where delay is
    not acceptable ?
  • QoS will be an issue

Challenges and Constraints
  • Wireless Networking
  • Sensing Range
  • Very small
  • Nodes might be close to each other
  • Data Redundancy
  • Coverage Problem

Challenges and Constraints
  • Decentralized Management
  • Requires Distributed Algorithms
  • Overhead might be imposed
  • Security
  • Exposed to malicious intrusions and attacks due
    to unattendance characteristics.
  • denial-of-service
  • jamming attack

In Network Processing
Enable Data Base Like Operations
Network Characteristics
  • Dense Node Deployment
  • Battery-Powered Sensors
  • Sever Energy , Computation , and Storage
  • Self Configurable
  • Application Specific
  • Unreliable Sensor Nodes
  • Frequent Topology Change
  • No Global Identifications
  • Many-to-One Traffic pattern ( multiple sources
    to a single Sink node)
  • Data Redundancy

Design Issues
  • Fault Tolerance
  • Large number of nodes already deployed or
  • Nodes do the same job. If one fails , the network
    still working because its neighbor monitors the
    same phenomenon .
  • Mobility
  • Helps nodes to reorganize themselves in case of a
    failure of any of the nodes
  • Attribute-Based Addressing
  • Addresses are composed of group of
    attribute-value pairs
  • Ex. lt temp gt 35, location area Agt

Design issues
  • Location Awareness
  • Nodes data reporting is associated with location
  • Priority Based Reporting
  • Nodes should adapt to the drastic changes in the
  • Query Handling
  • The sink node / user should be able to query the
  • The response should be routed to the originator
  • We might have multiple sinks in the network

Traditional networks Vs. wireless sensor networks
Traditional Networks Wireless Sensor Networks
General-purpose design serving many applications Single-purpose design serving one specific application
Typical primary design concerns are network performance and latencies energy is not a primary concern Energy is the main constraint in the design of all node and network components
Networks are designed and engineered according to plans Deployment, network structure, and resource use are often ad-hoc (without planning)
Devices and networks operate in controlled and mild environments Sensor networks often operate in environments with harsh conditions
Maintenance and repair are common and networks are typically easy to access Physical access to sensor nodes is often difficult or even impossible
Component failure is addressed through maintenance and repair Component failure is expected and addressed in the design of the network
Obtaining global network knowledge is typically feasible and centralized management is possible Most decisions are made localized without the support of a central manager