wireless sensor networksjain/cse574-10/ftp/j_mssr.pdf20-1 washington university in st. louis cse574s...
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20-1©2010 Raj JainCSE574sWashington University in St. Louis
Wireless Sensor NetworksWireless Sensor Networks
Raj Jain Washington University in Saint Louis
Saint Louis, MO [email protected]
Audio/Video recordings of this lecture are available at:http://www.cse.wustl.edu/~jain/cse574-10/
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20-2©2010 Raj JainCSE574sWashington University in St. Louis
OverviewOverview
Sensor Applications
IEEE 802.15.4-2006
6LowPAN
WirelessHART
Research Issues
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20-3©2010 Raj JainCSE574sWashington University in St. Louis
Sensor ApplicationsSensor ApplicationsBattlefield Surveillance Chemical, Biological Weapons
Habitat exploration of animals Patient heart rate, blood pressure
Crops and AgricultureForest Fires and Flood Detection
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20-4©2010 Raj JainCSE574sWashington University in St. Louis
Sensor (vs. AdSensor (vs. Ad--Hoc)Hoc)
Large scaleBatteries may not be replaceableMay not have global identifiersQueries 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 aggregation
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20-5©2010 Raj JainCSE574sWashington University in St. Louis
IEEE 802.15.4IEEE 802.15.4--20062006Low-Rate Wireless Personal Area NetworkPhysical layer used in ZigBee, WirelessHART, MiWi which add upper layers10 m reach at 250 kbps (20/40/100 kbps versions)Three Frequency Bands:
868.0-868.6 MHz in Europe902-928 Mhz in North America2400-2383.5 MHs worldwide
Uses Direct Sequence Spread Spectrum (DSS)BPSK or QPSK modulationIEEE 802.15.4a-2007 added ultra-wideband, and chirp spread spectrumIEEE 802.15.4c-2009, IEEE 802.15.4d-2009 adde more PHYsand modulations
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20-6©2010 Raj JainCSE574sWashington University in St. Louis
IEEE 802.15.4 TopologiesIEEE 802.15.4 TopologiesStar, Peer-to-peer, Structured starFull function and reduced function devices
Two modes:With Beacon: Coordinator sends start beacon and stop beacon to indicate active time.
The time is slotted. Slotted CSMA/CA. Transmissions end at second beacon.
Without Beacon: Unslotted CSMA/CA protcol with random exponential backoff
Ref: http://en.wikipedia.org/wiki/802.15.4
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20-7©2010 Raj JainCSE574sWashington University in St. Louis
6LowPAN6LowPANIETF Working Group: IPv6 over Lower Power Wireless Personal Area Networks (IPv6 over IEEE 802.15.4)IEEE 802.15.4 allows 127 byte packets minus 25 byte framing overhead minus 21 bytes for AES security = 81 byte IP packetIPv6 requires a min transmission unit (MTU) of 1280 bytes.
Need to compress IPv6 headers. 64-bit Extended IEEE 802 addresses or 16-bit local IDs are used
6LowPAN defined an adoption layer that compresses IPv6 headers and allows PANs to be connected to regular IPv6 networks.REF: RFC 4944, Transmission of IPv6 Packets over IEEE 802.15.4 NetworksRFC 4919: IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):Overview, Assumptions, Problem Statement, and Goals
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20-8©2010 Raj JainCSE574sWashington University in St. Louis
WirelessHARTWirelessHART
A commonly used sensor network protocol stack
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20-9©2010 Raj JainCSE574sWashington University in St. Louis
HARTHARTHighway Addressable Remote TransducerCommunication between smart devices and monitoring systems4-20 mA current loop is a commonly used analog measurement techniqueLow level frequency shift keying (FSK) over 4-20 mA analog signal. 1200 bps.
Master/slave protocol with two masters (primary, secondary)Point-to-point or multi-drop configuration
Full 7 layer stackRef:http://www.hartcomm.org/protocol/about/aboutprotocol_how.html
TimeSignal
I/O Subsystem
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20-10©2010 Raj JainCSE574sWashington University in St. Louis
HART ProtocolsHART ProtocolsFull stack: Layer 1, 2, 3, 4, and 7Layer 1: FSKLayer 2: Master-Slave. Upto 15 devices in a multi-drop lineLayer 3: Routing, securityLayer 4: end-to-endlayer 7: Commands, response, data types, and statusDevice Description: Like a MIB
Specifies the functions and features of a deviceDevice description languageAllows manufacturer specific featuresCan be compiled to create management screens for devices
Ref:http://www.hartcomm.org/protocol/about/aboutprotocol_specs.htmlhttp://www.hartcomm.org/hcf/documents/documents_spec_list.html
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20-11©2010 Raj JainCSE574sWashington University in St. Louis
WirelessHARTWirelessHART
Extension of HART to WirelessSupports star and mesh topologiesSelf-organizing and self-healingUses IEEE 802.15.4-2006 radios in 2.4GHzFrequency hopping with blacklisting to avoid used channels128-bit AES encryptionUses multi-path routing. Messages alternate paths to ensure secondary paths are up.
Ref: http://www.hartcomm.org/protocol/wihart/wireless_how_it_works.htmlhttp://www.hartcomm.org/protocol/training/training_resources_wihart.html
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20-12©2010 Raj JainCSE574sWashington University in St. Louis
WirelessHART WirelessHART Field DevicesField DevicesWirelessHART adapter or builtinGateways: Connect to the backbone networkNetwork Manager: Manages routes, monitors health (can be integrated in to gateways or hosts)Security Manager: Contains list of authorized devices. Distributes security keys.Repeater: Extends the range.Adapter: Attaches to devices without wirelessHART
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20-13©2010 Raj JainCSE574sWashington University in St. Louis
Sensor NodeSensor Node
A device with sensors, networking hardware, and powerSmall size ⇒ Dust or MotesDARPA funded Smart Dust project (Dust Network, Inc. is a Silicon valley startup for Motes)TinyOS is a public domain operating system designed for sensor nodes
Transceiver Sensor 1
Sensor 2
A/D Converter
Memory
Power Microcontroller
Ref: http://en.wikipedia.org/wiki/Moteshttp://en.wikipedia.org/wiki/Smartdust
http://en.wikipedia.org/wiki/TinyOShttp://en.wikipedia.org/wiki/Dust_Networks
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20-14©2010 Raj JainCSE574sWashington University in St. Louis
Research IssuesResearch Issues
1. Location Discovery2. Quality of a Sensor Network3. Time Synchronization4. Transport Layer Issues5. Real-Time Communication
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20-15©2010 Raj JainCSE574sWashington University in St. Louis
Location DiscoveryLocation DiscoveryLocation Stamp on dataIndoor Localization: Reference nodes in each locationAtomic Multi-Lateration: Need 3 referencesIterative Multi-Lateration: Nodes with known location become references for othersCollaborative Multi-Lateration: Use quadratic equations
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20-16©2010 Raj JainCSE574sWashington University in St. Louis
Global Positioning System (GPS)Global Positioning System (GPS)US Department of Defense $12BMan made stars24 Satellites and their ground stationsTriangulationMeasures travel time of radio signal ⇒ DistanceSatellites broadcast current time and their location using a Direct Sequence Code1023 chips per bit3 satellites give (x, y, z)4 satellites give (x, y, z, t)Correct for any delays experienced through the atmospherehttp://www.edu-observatory.org/gps/tutorials.html
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20-17©2010 Raj JainCSE574sWashington University in St. Louis
Quality of a Sensor NetworkQuality of a Sensor NetworkQuality = Coverage + ExposureExposure: Ability to observe a target.Ability decreases with the distance from the targetCoverage: How well is the region covered with sensorsFind the least covered path that could be followed by enemyVoronoi Diagram: Cost = Distance from nearest sensorFind the maximum cost path. Opposite Problem: Find the best covered path
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20-18©2010 Raj JainCSE574sWashington University in St. Louis
Time SynchronizationTime SynchronizationGPS not accessible inside buildings, under water.Send a time stamp to neighborOne-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 receiverPost Facto Synchronization:
Announce time along with the event. Everyone else synchronizes to itLeader periodically sends sync messages, which are floodedDistributed election of the leader based on a random number
Resynchronization: Upon merger of partitions. Better to advance the clock
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20-19©2010 Raj JainCSE574sWashington University in St. Louis
Transport Layer IssuesTransport Layer IssuesReliable transmission of data from sources to sinks
PSFQ:
Ask previous hop to retransmit if error ⇒ Fetch
Forward to next hops ⇒ PumpPump slowly and fetch quickly (PSFQ) ⇒ Minimize storage, maximize reliabilityFarthest node sends a report of delivery status to the source. Intermediate nodes append their status to the same message.
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20-20©2010 Raj JainCSE574sWashington University in St. Louis
RealReal--Time CommunicationTime CommunicationSPEED: Geographical routing ⇒ Send packets to neighbors in the direction of the destinationNodes send delay feedback backwards as packets are forwardedNodes can also send a backpressure message if delay too highSelect the neighbor with least delayIf no neighbor can meet the delay constraint, the packet is droppedNo node close to the destination ⇒ VoidVoid avoidance ⇒ Issue a back-pressure with infinite delay ⇒ Search for alternate paths
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20-21©2010 Raj JainCSE574sWashington University in St. Louis
SummarySummary
IEEE 802.15.4 PHY layer is designed for sensor networksZigBEE and WirelessHART are two common protocol stacksLocation Discovery is by triangulation or multi-laterationQuality of a Sensor Net is measured by coverage and exposureTime Synchronization by exchanging timestampsTransport: Pump slowly and fetch quickly increases reliabilityReal-Time Communication using deadline based forwarding
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20-22©2010 Raj JainCSE574sWashington University in St. Louis
Related Wikipedia ArticlesRelated Wikipedia Articleshttp://en.wikipedia.org/wiki/Category:Wireless_sensor_networkhttp://en.wikipedia.org/wiki/Wireless_sensor_networkhttp://en.wikipedia.org/wiki/Body_sensor_networkhttp://en.wikipedia.org/wiki/Intelligent_sensorhttp://en.wikipedia.org/wiki/Key_distribution_in_wireless_sensor_networkshttp://en.wikipedia.org/wiki/Location_estimation_in_sensor_networkshttp://en.wikipedia.org/wiki/Semantic_Sensor_Webhttp://en.wikipedia.org/wiki/SensorMLhttp://en.wikipedia.org/wiki/Sensor_Web
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20-23©2010 Raj JainCSE574sWashington University in St. Louis
Related Wikipedia Articles (Cont)Related Wikipedia Articles (Cont)http://en.wikipedia.org/wiki/Sensor_gridhttp://en.wikipedia.org/wiki/Sensor_nodehttp://en.wikipedia.org/wiki/Smartdusthttp://en.wikipedia.org/wiki/TinyOShttp://en.wikipedia.org/wiki/Virtual_Sensor_Networkshttp://en.wikipedia.org/wiki/Visual_sensor_networkhttp://en.wikipedia.org/wiki/WirelessHARThttp://en.wikipedia.org/wiki/Secure_Data_Aggregation_in_WSNhttp://en.wikipedia.org/wiki/ZigBeehttp://en.wikipedia.org/wiki/Dust_Networks
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20-24©2010 Raj JainCSE574sWashington University in St. Louis
Reading AssignmentReading Assignment
Read Chapter 12 of Murthy and Manoj
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20-25©2010 Raj JainCSE574sWashington University in St. Louis
HomeworkHomework
A node X receives three beacons from nodes A, B, and C at (0, 0, 0), (2, 6, 0), and (3, 4, 0), respectively. From the received signal strengths, it determines the distances to A, B, and C to be √26, √6, and √11, respectively. Find the coordinates of X.
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20-26©2010 Raj JainCSE574sWashington University in St. Louis
List of AcronymsList of AcronymsBS Base StationGPS Global Positioning SystemID IdentifierLEAP Localized Encryption and Authentication ProtocolMAC Media Access ControlPEGASIS Power-Efficient Gathering for Sensor Information SystemsPHY Physical LayerPSFQ Pump slowly and fetch quicklySPEED Speed (Not an acronym)TDMA Time Division Multiple Access