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Chapter 2

Chapter 2 . Wireless Sensor Networks. Smart Environments---. Huge challenge Detect, monitor, collect data Asses & evaluate data Formulate displays; make decisions Need information –internal, external Wireless Sensor Nets provide a possible solution. Wireless Sensor Nets.

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Chapter 2

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  1. Chapter 2 Wireless Sensor Networks

  2. Smart Environments--- • Huge challenge • Detect, monitor, collect data • Asses & evaluate data • Formulate displays; make decisions • Need information –internal, external • Wireless Sensor Nets provide a possible solution

  3. Wireless Sensor Nets • Chapter includes large amount of networking information • Communication NW • Wireless Sensor nets • Smart Sensors • More….. • We will do an overview

  4. Network Communication • Quantity & Quality of Service (QoS) • Thruput & delays, time, loss, errors, power consumption • Topologies • Star, ring, bus • Mesh, tree • Fully connected

  5. Communication Protocols & Routing • Message header • Source, destination, etc. • Switching • Store--&--forward - buffer • Virtual cut through – header goes on • Worm hole – split message • Multiple access protocols – multiple nodes • Avoid collisions & lost data • Network Layers – 7 - OSI/RM • Open Systems Interconnection Reference Model

  6. Routing • Path from source to destination • Performance: QoS • throughput; average packet delay • Routing methods • Fixed • Adaptive • Minimum cost -- shortest path

  7. Routing • Deadlock: all nodes waiting, buffer full • Live lock: message continuously transmitted & never teaches destination • Flow control • Queues & buffers • To protect network from overload & speed mismatches; maintain QoS; freedom from deadlock

  8. Power Management • How do we power remote networks? • How do you “replace batteries”? • What is lifetime of a nw? • How can we conserve power? • MEMS (microelectromechanical systems) are under development

  9. Power Management • RFID -- radio frequency identification • Passive: no power source • Active: battery • Example: toll collection • Distance • RFID – ~25 feet • Power required for transmission increases as square of distance • Short hops vs. long distance

  10. History of Network Standards • Ethernet: mid 1970's, standardized 1979 • IEEE 802.3 • Official IEEE Ethernet standard--1983 • Fast Ethernet (10x) -- 1995 • Token Ring -- 1984 • IEEE standard -- 802.5 • High cost • ANSI Fiber optic standard--mid 1980's • Higher speed

  11. History of Network Standards 3. Gigabit Ethernet -- 1996 • GE standards -- 1999 • Supports (development of) • Client-server networks • Peer-to-Peer networks • All have equal authority • Peer-to-Peer computing (P2P) • Tasks are divided

  12. History of Network Standards 4. Wireless LAN (WLAN) -- 1997 • IEEE 802.11 standard • WiFi 802.11b • Bluetooth -- WPAN -- IEEE 802.15 • Short range RF

  13. Wireless Sensor Network • Key to gathering information for smart environments • Easy & fast installation • IEEE 1451 standards (1993) • Compatibility among manufacturers

  14. Sensors • Sensor: responds to signal (passive) • Smart Sensor: provides extra functions beyond those necessary for generating accurate representation of the sensed quantity • Virtual Sensor: physical sensor/transducer plus the associated signal conditionery & DSP required to obtain reliable estimates of the required sensory information (component of Smart Sensor) Omit section 2.3.2

  15. Self-Organization • Deployment: by ships or aircraft • Communication: wake-up, detect each, form communication network • Positioning • Relative: distributed signal processing • Absolute: reporting data related to detected target

  16. Relative Positioningaka Localization • For internode communication • Measure distances • Relatively Calibrated • Relative positions of all nodes in network are known

  17. Absolute Geographic Positioning • (Fully) Calibrated • Absolute (actual) position of each node is known • How? GPS, landmarks, beacons, etc. • At least 3 nodes in nw must know their location

  18. Ultra Wideband Radio -- WWB • Good for distributed sensor nets • Short range • Penetrates walls • Time-of-flight properties (distance) • Down to 1 cm • Range 40 meters • Very small

  19. Signal Processing/Decision Making Issues • SC -- Signal Conditioning • Noise, low amplitude, biased due to other factors such as temperature • Solutions: temperature, compensation, low-pass filtering

  20. Digital Signal Processing --DSP Sensor fusion: combining readings from many different types of sensors (e.g. seismic, acoustic, temperature) Kalman Filter: a DSP tool used to combine information from multiple sensors • Example: space program -- moon, distant probes • Reconstructs (estimates) full internal state of a system from a few measured outputs

  21. LabView • A software product from National Instruments • Popular, powerful, easy to use • Provides • Advanced DSP • Intelligent user interfaces (pg. 43) • Decision assistance • Alarm function

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