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Introduction to Distributed Networks
Wireless Sensor Networks
Rabie A. Ramadan, PhDCairo University
http://rabieramadan.org
1
Class Format Presentations by myself and others Assignments Survey on one of the following topics :
• Topics
• Survey Format
• Prepare a presentation for your topic – some will be publically presented and others will be in private
• 4 persons per survey (effort should be equivalent to the number of persons)
• Not less than 6 pages 3
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 his/her home to work,..
Disasters may be a drive force for such networks
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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)
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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 “TransducerTransducer” converts energy from one form to another.
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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, texture)
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An example of a sensor: Passive infrared
PIR is a differential sensor: detects target as it crosses the
“beams” produced by the optic
Communication Unit
Sensing Unit
Sensors
ADC
Processing Unit
Processor
Storage
Power Unit
Mobility Support Unit Location Finding Unit
What is a Smart Sensor Node?
Sensors Classification
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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
Physical property to be monitored determines type of required sensor
Other Classifications Power supply: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 .
Electrical phenomenon:Electrical phenomenon:
• resistive sensors use changes in electrical resistivity (ρ) based on physical properties such as temperature
• capacitive sensors use changes in capacitor dimensions or permittivity (ε) based on physical properties
• 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
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 Wireless Sensor Networks
DARPA:
• Distributed Sensor Nets Workshop (1978)
• Distributed Sensor Networks (DSN) program (early 1980s)
• Sensor Information Technology (SensIT) program UCLA and Rockwell Science Center
• Wireless Integrated Network Sensors (WINS)
• Low Power Wireless Integrated Microsensor (LWIM) (1996) 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)
Commercial Effort
Crossbow (www.xbow.com), Sensoria (www.sensoria.com), Worldsens (http://worldsens.citi.insa-lyon.fr), Dust Networks
(http://www.dustnetworks.com ), and Ember Corporation (http://www.ember.com ).
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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)
• Node’s layers must be designed carefully.
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Wireless Range Controls the Network Topology
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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
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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-hopmulti-hop communication and try to avoid it.
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Operating System Operating System
Energy affects the O.S. design : Energy affects the O.S. design : • Small memory footprint,
• Efficient switching between tasks
• security mechanisms
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Challenges and Constraints
Self-Management• Sensors usually deployed in harsh environment.
• There is no pre-infrastructure setup.
• Once deployed, must operate without human intervention
• Sensor nodes must be self-managing in that • They configure themselves,
• Operate and collaborate with other nodes,
• Adapt to failures, changes in the environment,
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A A self-managing Network self-managing Network Self-organization
• A network’s ability to adapt configuration parameters based on system and Environmental state.
Self-optimization
• A device’s 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.
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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
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Challenges and ConstraintsChallenges and Constraints
Wireless Networking• Communication range
• Communication ranges are always short
• It is required for the network to be highly connected
• Routing paths will be long
• What about critical applications where delay is not acceptable ?
• QoS will be an issue
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Challenges and Constraints
Wireless Networking
• Sensing Range
• Very small
• Nodes might be close to each other
• Data Redundancy
• Coverage Problem
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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 attack36
Network Characteristics Dense Node Deployment Battery-Powered Sensors Sever Energy , Computation , and Storage Constraints 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
39
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. < temp > 35, location = area A>
Design issues Location Awareness
• Nodes’ data reporting is associated with location
Priority Based Reporting
• Nodes should adapt to the drastic changes in the environment
Query Handling • The sink node / user should be able to query the network
• The response should be routed to the originator
• We might have multiple sinks in the network
Traditional networks Vs. wireless sensor networks
42
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