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Overview of Wireless Sensor Networks

This lecture provides an overview of wireless sensor networks, including architecture, hardware, applications, and design issues. It also discusses key technologies and concepts related to sensor networks.

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Overview of Wireless Sensor Networks

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  1. ECE/CSC 575 – Section 1 Introduction to Wireless Networking Lecture 23Dr. Xinbing Wang

  2. Overview of the Course • Part 1: Wireless communication systems (Chapter 1) • Flexibility to support roaming • Limitations: Geographical coverage, transmission rate, and transmission errors • Part 2: Wireless communication technology • Radio propagation (Chapter 5) • Spread spectrum (Chapter 7) • Part 3: Current wireless systems • Cellular network architecture (Chapter 10) • Mobile IP (Chapter 12) • Wireless LAN (Chapter 11/13/14) • Part 4: Other wireless networks • Ad hoc networks (Reading materials) • Sensor networks (Reading materials) • Wireless PAN (Chapter 15) • Satellite systems (Chapter 9) • Part 5: Wireless Security Dr. Xinbing Wang

  3. Wireless Sensor Networks • Architecture • Hardware and examples • Applications • Design issues: hardware, fault tolerance, energy conservation and so on. Dr. Xinbing Wang

  4. Several thousand nodes Nodes are tens of feet of each other Densities as high as 20 nodes/m3 Sink Internet, Satellite, etc Sink Task Manager Architecture • I.F.Akyildiz, W.Su, Y. Sankarasubramaniam, E. Cayirci, “Wireless Sensor Networks: A Survey”, Computer Networks (Elsevier) Journal, March 2002. Dr. Xinbing Wang

  5. Key technologies that enable sensor networks: • Micro electro-mechanical systems (MEMS) • Wireless communications • Digital electronics Dr. Xinbing Wang

  6. Sensor Network Concepts • Sensors nodes are very close to each other • Sensor nodes have local processing capability • Sensor nodes can be randomly and rapidly deployed even in places inaccessible for humans • Sensor nodes can organize themselves to communicate with an access point • Sensor nodes can collaboratively work Dr. Xinbing Wang

  7. Location Finding System Mobilizer Transceiver Sensor ADC Processor Memory Power Generator Power Unit Sensor Node Hardware • Small • Low power • Low bit rate • High density • Low cost (dispensable) • Autonomous • Adaptive SENSING UNIT PROCESSING UNIT Dr. Xinbing Wang

  8. Berkeley Motes Dr. Xinbing Wang

  9. Specifications of the Mote Dr. Xinbing Wang

  10. UC Berkeley: Smart Dust UCLA: WINS UC Berkeley: COTS Dust JPL: Sensor Webs Rockwell: WINS Examples of Sensors Dr. Xinbing Wang

  11. Sensor Networks Applications Sensors can monitor ambient conditions including: • Temperature • Humidity • Vehicular movement • Lightning condition • Pressure • Soil makeup • Noise levels • The presence or absence of certain kinds of objects • Mechanical stress levels on attached objects, and • Current characteristics (speed, direction, size) of an object Dr. Xinbing Wang

  12. Sensor Networks Applications (2) Sensors can also be used for : • Sensing • Event detection • Event identification • Location sensing • Local control of actuators Dr. Xinbing Wang

  13. Sensor Networks Military Applications Command, control, communications, computing, intelligence, surveillance, reconnaissance, targeting (C4SRT) • Monitoring friendly forces, equipment and ammunition • Battlefield surveillance • Reconnaissance of opposing forces and terrain • Targeting • Battle damage assessment • Nuclear, biological and chemical (NBC) attack detection and reconnaissance Dr. Xinbing Wang

  14. Sensor Networks Applications (2) Sensors can also be used for : • Sensing • Event detection • Event identification • Location sensing • Local control of actuators Dr. Xinbing Wang

  15. Factors Influencing Sensor Network Design A. Fault Tolerance (Reliability) B. Scalability C. Production Costs D. Hardware Constraints E. Sensor Network Topology F. Operating Environment G. Transmission Media H. Power Consumption Dr. Xinbing Wang

  16. A. Fault Tolerance (Reliability) • Sensor nodes may fail or be blocked due to lack of power have physical damage, or environmental interference. • The failure of sensor nodes should not affect the overall task of the sensor network. • This is called RELIABILITY or FAULT TOLERANCE, i.e., ability to sustain sensor network functionality without any interruption Dr. Xinbing Wang

  17. Fault Tolerance (2) • Reliability (Fault Tolerance) of a sensor node is modeled: i.e., by Poisson distribution, to capture the probability of not having a failure within the time interval (0,t) with lambda_k is the failure rate of the sensor node k and t is the time period. G. Hoblos, M. Staroswiecki, and A. Aitouche, “Optimal Design of Fault Tolerant Sensor Networks,” IEEE International Conference on Control Applications, pp. 467-472, Anchorage, AK, September 2000. Dr. Xinbing Wang

  18. Fault Tolerance (3) • Reliability (Fault Tolerance) of a broadcast range with N sensor nodes is calculated from: Dr. Xinbing Wang

  19. Fault Tolerance (4) • EXAMPLE: How many sensor nodes are needed within a broadcast radius (range) to have 99% fault tolerated network? • Assuming all sensors within the radio range have same reliability, prev. equation becomes Drop t and substitute f = (1 – R). o.99 = 1 – fN  N = 2 Dr. Xinbing Wang

  20. Fault Tolerance (5) REMARK: 1. Protocols and algorithms may be designed to address the level of fault tolerance required by sensor networks. 2. If the environment has little interference, then the requirements can be more relaxed. Dr. Xinbing Wang

  21. Factors Influencing Sensor Network Design  A. Fault Tolerance (Reliability) B. Scalability C. Production Costs D. Hardware Constraints E. Sensor Network Topology F. Operating Environment G. Transmission Media H. Power Consumption  Dr. Xinbing Wang

  22. B. Scalability • The number of sensor nodes may reach millions in studying a field/application • The density of sensor nodes can range from few to several hundreds in a region (cluster) which can be less than 10m in diameter. Dr. Xinbing Wang

  23. Scalability (2) • The Sensor Node Density: i.e., the number of expected nodes within the radio range R where N is the number of scattered sensor nodes in region A and R is the radio transmission range. Basically:  is the number of sensor nodes within the transmission radius of each sensor node in region A. The number of sensor nodes in a region is used to indicate the node density depends on the application. Dr. Xinbing Wang

  24. Scalability (3) EXAMPLE: Assume sensor nodes are evenly distributed in the sensor field, determine the node density if 200 sensor nodes are deployed in a 50x50 m2 region where each sensor node has a broadcast radius of 5 m. Use the eq. on the previous slide  (R) = (200 * * 52 )/(50*50) = 2 *  Dr. Xinbing Wang

  25. Example -- Node Distribution Dr. Xinbing Wang

  26. Scalability (4) -- Network Configuration dnei Expected distance to the nearest neighbor, may or may not be communicating neighbor. dhop  Expected distance to the next hop, i.e., distance to communicating neighbor. dhop>=dnei Assuming that connection establishment is equally likely with any node within the radio range R of the given node, the expectedhop distance is: Sink node dhop = 2R/3 Radio Range R e.g., R=20m  13.33m dnei dhop Sensor nodes Dr. Xinbing Wang

  27. Scalability (5) -- Examples • Machine Diagnosis Application: less than 300 sensor nodes in a 5 m x 5 m region. • Vehicle Tracking Application:Around 10 sensor nodes per cluster/region. • Home Application:2 dozens or more. • Habitat Monitoring Application: Range from 25 to 100 nodes/cluster • Personal Applications:Ranges from 100s to 1000s, e.g., clothing, eye glasses, shoes, watch, jewelry. Dr. Xinbing Wang

  28. Factors Influencing Sensor Network Design  A. Fault Tolerance (Reliability) B. Scalability C. Production Costs D. Hardware Constraints E. Sensor Network Topology F. Operating Environment G. Transmission Media H. Power Consumption   Dr. Xinbing Wang

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