WUSTL CSE 574S - Wireless Sensor Network - D79006

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WUSTL CSE 574S - Wireless Sensor Network

School name Washington University in St. Louis

Course Cse 574s- Wireless and Mobile Networking

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Wireless Sensor NetworksOverviewSensor ApplicationsSensor (vs. Ad-Hoc)Sensor Network ArchitectureData DisseminationDirected DiffusionGeographic Hash tableData GatheringMAC Protocols for Sensor NetworksLocation DiscoveryGlobal Positioning System (GPS)Quality of a Sensor NetworkSensor StandardsTime SynchronizationTransport Layer IssuesSensor Network SecurityReal-Time CommunicationSummaryReading AssignmentHomework17-1©2006 Raj JainCSE574sWashington University in St. LouisWireless Sensor Wireless Sensor NetworksNetworksRaj Jain Washington University in Saint LouisSaint Louis, MO [email protected] slides are available on-line at:http://www.cse.wustl.edu/~jain/cse574-06/17-2©2006 Raj JainCSE574sWashington University in St. LouisOverviewOverviewSensor ApplicationsSensor Network ArchitectureData DisseminationMAC Protocols for Sensor NetworksLocation DiscoveryQuality of a Sensor NetworkTime SynchronizationTransport Layer IssuesSensor Network SecurityReal-Time Communication17-3©2006 Raj JainCSE574sWashington University in St. LouisSensor ApplicationsSensor ApplicationsBattlefield Surveillance Chemical, Biological WeaponsHabitat exploration of animalsPatient heart rate, blood pressureCrops and AgricultureForest Fires and Flood Detection17-4©2006 Raj JainCSE574sWashington University in St. LouisSensor (vs. Ad-Hoc)Sensor (vs. Ad-Hoc)Large scaleBatteries may not be replaceableMay not have global identifiersQueries may be data centric rather than address centric:Who's temperature is more than 95 degree vs. What is your temperature? Geographical routing, Data fusion, Data aggregation17-5©2006 Raj JainCSE574sWashington University in St. LouisSensor Network ArchitectureSensor Network Architecture1. Layered: Base station, one-hop layer, 2-hop layer, ...2. Clustered: Nodes elect and communicate through cluster heads17-6©2006 Raj JainCSE574sWashington University in St. LouisData DisseminationData DisseminationSources, Sinks , and Eve nt sData Gathering: Sources send periodically to central collection points (base station) Data Diffusion: Sinks propagate their interests (type of data or event) Nodes cache interests and report events when detectedFlooding: Implosion (duplicate messages), overlap (multiple sources), blind (no consideration of energy or resources)Gossiping: Randomly select a neighborSinksSources17-7©2006 Raj JainCSE574sWashington University in St. LouisDirected DiffusionDirected DiffusionSensor nodes generate queries. Flooded to entire network.Intermediate node cache the queries and the previous neighbor A gradient (= rate) is applied at each hop to the queryData is propagated along the reverse path proportional to the gradientSink can reinforce a path by requesting higher rates along that pathACDFEBEventSinkACDFEBEventSinkSourceACDFEBSinkSourceACDFEBSinkSource17-8©2006 Raj JainCSE574sWashington University in St. LouisGeographic Hash tableGeographic Hash tableQuery (key) is hashed in a (x,y) coordinate and is sent to a node nearest to that coordinate  Home Location (k)The data is hashed and sent to its home location from where it is propagated to the sinks  Uniform Storage loadRedundancy can be used for home locationSinkSourceHomeLocation17-9©2006 Raj JainCSE574sWashington University in St. LouisData GatheringData GatheringGathering  From all sensor nodes to the BSMinimize delay × energyPEGASIS: Power-Efficient Gathering for Sensor Information SystemsEach nodes combines its data in the message and sends to its nearest neighbor not visited beforeStarting from the farthest nodeEnding at the leader which passes it to the baseA Token is passed backwards from the leader17-10©2006 Raj JainCSE574sWashington University in St. LouisMAC Protocols for Sensor NetworksMAC Protocols for Sensor NetworksThree types:1. Fixed Allocation: Predetermined assignment2. Demand Based: Based on need3. Contention based: No delay guaranteeSelf-Organizing MAC for Sensors (SMACS):Capacity >> Data rateNeighbors synchronize and agree on times for transmissionOnly neighbors synchronize  Synch energy savedSleep when not transmitting  Further energy savingsTDMA, FDMA, TDMA/FDMA, CSMA are also possibleBluetooth, 802.11, and ZigBee are MACs used in practice17-11©2006 Raj JainCSE574sWashington University in St. LouisLocation DiscoveryLocation DiscoveryLocation Stamp on dataIndoor Localization: Reference nodes in each locationAtomic Multi-Lateration: Need 3 referencesIterative Multi-Lateration: Nodes with known location become references for othersCollaborative Multi-Lateration: Use quadratic equations17-12©2006 Raj JainCSE574sWashington University in St. LouisGlobal Positioning System (GPS)Global Positioning System (GPS)US Department of Defense $12BMan made stars24 Satellites and their ground stationsTriangulationMeasures travel time of radio signal  DistanceSatellites broadcast current time and their location using a Direct Sequence Code1023 chips per bit3 satellites give (x, y, z)4 satellites give (x, y, z, t)Correct for any delays experienced through the atmospherehttp://www.edu-observatory.org/gps/tutorials.html17-13©2006 Raj JainCSE574sWashington University in St. LouisQuality of a Sensor NetworkQuality of a Sensor NetworkQuality = Coverage + ExposureExposure: Ability to observe a target.Ability decreases with the distance from the targetCoverage: How well is the region covered with sensorsFind the least covered path that could be followed by enemyVoronoi Diagram: Cost = Distance from nearest sensorFind the maximum cost path. Opposite Problem: Find the best covered path17-14©2006 Raj JainCSE574sWashington University in St. LouisSensor StandardsSensor Standards802.11, Bluetooth, ZigBeeIEEE 1451: Smart Transducer Interface for Sensors and ActuatorsSeven parts 1451.0 through 1451.6 dealing with different issues1451.5 is wireless interface - specifies 802.11, bluetooth and ZigBee17-15©2006 Raj JainCSE574sWashington University in St. LouisTime SynchronizationTime SynchronizationGPS not accessible inside buildings, under water.Send a time stamp to neighborOne-way Delay = Send Time (Preparing the message) + Access Time (media access) + propagation time + receive time (processing at receiver)Best to timestamp the message at the PHY layer of the receiverPost Facto

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