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Lect-4 Basics_of_Wireless_Sensor_Networks.ppt
- 1. Introduction to Wireless Sensor Networks
- 2. Sensing and Sensors Sensing: technique to gather information about physical objects or areas Sensor (transducer): object performing a sensing task; converting one form of energy in the physical world into electrical energy Examples of sensors from biology: the human body eyes: capture optical information (light) ears: capture acoustic information (sound) nose: captures olfactory information (smell) skin: captures tactile information (shape, texture)
- 3. Sensing (Data Acquisition) Sensors capture phenomena in the physical world (process, system, plant) Signal conditioning prepare captured signals for further use (amplification, attenuation, filtering of unwanted frequencies, etc.) Analog-to-digital conversion (ADC) translates analog signal into digital signal Digital signal is processed and output is often given (via digital-analog converter and signal conditioner) to an actuator (device able to control the physical world)
- 4. Sensor Classifications • Physical property to be monitored determines type of required sensor
- 5. 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
- 6. History of Wireless Sensor Networks
- 8. History of Wireless Sensor Networks Recent commercial efforts Crossbow (www.xbow.com) Sensoria (www.sensoria.com) Worldsens (worldsens.citi.insa-lyon.fr) Dust Networks (www.dustnetworks.com) Ember Corporation (www.ember.com)
- 9. WSN Communication • Characteristics of typical WSN: • low data rates (comparable to dial-up modems) • energy-constrained sensors • IEEE 802.11 family of standards • most widely used WLAN protocols for wireless communications in general • can be found in early sensor networks or sensors networks without stringent energy constraints • IEEE 802.15.4 is an example for a protocol that has been designed specifically for short-range communications in WSNs • low data rates • low power consumption • widely used in academic and commercial WSN solutions
- 10. Single-Hop versus Multi-Hop • Star topology: • every sensor communicates directly (single-hop) with the base station • may require large transmit powers and may be infeasible in large geographic areas • Mesh topology • sensors serve as relays (forwarders) for other sensor nodes (multi-hop) • may reduce power consumption and allows for larger coverage • introduces the problem of routing
- 11. Challenges in WSNs: Energy • Sensors typically powered through batteries • replace battery when depleted • recharge battery, e.g., using solar power • discard sensor node when battery depleted • For batteries that cannot be recharged, sensor node should be able to operate during its entire mission time or until battery can be replaced • Energy efficiency is affected by various aspects of sensor node/network design • Physical layer: • switching and leakage energy of CMOS-based processors ECPU Eswitch Eleakage Ctotal *Vdd 2 Vdd * Ileak * t
- 12. • Medium access control layer: • contention-based strategies lead to energy-costly collisions • problem of idle listening • Network layer: • responsible for finding energy-efficient routes • Operating system: • small memory footprint and efficient task switching • Security: • fast and simple algorithms for encryption, authentication, etc. • Middleware: • in-network processing of sensor data can eliminate redundant data or aggregate sensor readings
- 13. Challenges in WSNs: Self-Management • Ad-hoc deployment • many sensor networks are deployed “without design” • sensors dropped from airplanes (battlefield assessment) • sensors placed wherever currently needed (tracking patients in disaster zone) • moving sensors (robot teams exploring unknown terrain) • sensor node must have some or all of the following abilities • determine its location • determine identity of neighboring nodes • configure node parameters • discover route(s) to base station • initiate sensing responsibility
- 14. Challenges in WSNs: Self-Management • Unattended operation • once deployed, WSN must operate without human intervention • device adapts to changes in topology, density, and traffic load • device adapts in response to failures • Other terminology • self-organization is the ability to adapt configuration parameters based on system and environmental state • self-optimization is the ability to monitor and optimize the use of the limited system resources • self-protection is the ability recognize and protect from intrusions and attacks • self-healing is the ability to discover, identify, and react to network disruptions
- 15. Challenges in WSNs: Wireless Networks •Wireless communication faces a variety of challenges •Attenuation: • limits radio range •Multi-hop communication: • increased latency • increased failure/error probability • complicated by use of duty cycles
- 16. Challenges in WSNs: Decentralization • Centralized management (e.g., at the base station) of the network often not feasible to due large scale of network and energy constraints • Therefore, decentralized (or distributed) solutions often preferred, though they may perform worse than their centralized counterparts • Example: routing • Centralized: • BS collects information from all sensor nodes • BS establishes “optimal” routes (e.g., in terms of energy) • BS informs all sensor nodes of routes • can be expensive, especially when the topology changes frequently • Decentralized: • each sensors makes routing decisions based on limited local information • routes may be non optimal, but route establishment/management can be much cheaper
- 17. Challenges in WSNs: Design Constraints • Many hardware and software limitations affect the overall system design • Examples include: • Low processing speeds (to save energy) • Low storage capacities (to allow for small form factor and to save energy) • Lack of I/O components such as GPS receivers (reduce cost, size, energy) • Lack of software features such as multi-threading (reduce software complexity)
- 18. Challenges in WSNs: Security • Sensor networks often monitor critical infrastructure or carry sensitive information, making them desirable targets for attacks • Attacks may be facilitated by: • remote and unattended operation • wireless communication • lack of advanced security features due to cost, form factor, or energy • Conventional security techniques often not feasible due to their computational, communication, and storage requirements • As a consequence, sensor networks require new solutions for intrusion detection, encryption, key establishment and distribution, node authentication, and secrecy
- 19. Comparison 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
- 20. Sensor networks VS ad hoc networks: •The number of nodes in a sensor network can be several orders of magnitude higher than the nodes in an ad hoc network. •Sensor nodes are densely deployed. •Sensor nodes are limited in power, computational capacities and memory. •Sensor nodes are prone to failures. •The topology of a sensor network changes frequently. •Sensor nodes mainly use broadcast, most ad hoc networks are based on p2p. •Sensor nodes may not have global ID.
- 21. Military applications Monitoring friendly forces, equipment and ammunition Reconnaissance of opposing forces and terrain Battlefield surveillance Battle damage assessment Nuclear, biological and chemical attack detection
- 23. Health applications • Tele-monitoring of human physiological data • Tracking and monitoring patients and doctors inside a hospital • Drug administration in hospitals • Intel deployed a 130-node network to monitor the activity of residents in an elder care facility. • Patient data is acquired with wearable sensing nodes (the “watch”) • Vital sign monitoring • Accident recognition • Monitoring the elderly
- 24. Environmental applications •Forest fire detection •Biocomplexity mapping of the environment •Flood detection •Precision agriculture Great Duck Island • 150 sensing nodes deployed throughout the island relay data temperature, pressure, and humidity to a central device. • Data was made available on the Internet through a satellite link.
- 25. Zebranet: a WSN to study the behavior of zebras • Special GPS-equipped collars were attached to zebras • Data exchanged with peer-to-peer info swaps • Coming across a few zebras gives access to the data
- 26. Interface electronics, radio and microcontroller Soil moisture probe Mote Antenna Gateway Server Internet Communications barrier Sensor field
- 28. Home and other commercial applications •Home automation and Smart environment •Interactive museums •Managing inventory control •Vehicle tracking and detection •Detecting and monitoring car thefts
- 31. Detecting and monitoring car thefts
- 32. 32 Traffic Management & Monitoring Future cars could use wireless sensors to: – Handle Accidents – Handle Thefts Sensors embedded in the roads to: –Monitor traffic flows –Provide real-time route updates
- 33. 33 Smart Home / Smart Office • Sensors controlling appliances and electrical devices in the house. • Better lighting and heating in office buildings. • The Pentagon building has used sensors extensively.
- 34. 34 Industrial & Commercial • Numerous industrial and commercial applications: • Agricultural Crop Conditions • Inventory Tracking • In-Process Parts Tracking • Automated Problem Reporting • RFID – Theft Deterrent and Customer Tracing • Plant Equipment Maintenance Monitoring
- 35. Usage of Sensor Networks Healthcare: Sensors can be used in biomedical applications to improve the quality of the provided care. Sensors are implanted in the human body to monitor medical problems like cancer and help patients maintain their health.
- 36. Mercury: A Wearable Sensor Network Platform for High-Fidelity Motion Analysis
- 37. SHIMMER wearable mote • developed by the Digital Health Group at Intel • TI MSP430 processor, • CC2420 IEEE 802.15.4 radio, • triaxial accelerometer, • rechargeable Li-polymer battery • MicroSD slot supporting up to 2 GBytes of Flash memory