1 CSE 466 - Winter 2008 Wireless Sensor Networks 1 Wireless Sensor Networks Important trend in embedded computing Connecting the physical world to the world of information Sensing (e.g., sensors) Actuation (e.g., robotics) Wireless sensor networks are enabled by three trends: Cheaper computation (Moore’s Law) Compact sensing (MEMS sensors) Wireless networking (low-power radios) CSE 466 - Winter 2008 Wireless Sensor Networks 2 What is embedded networked sensing? Embedded Networked Sensing Control system w/ small-form factor untethered nodes Exploit collaborative sensing and action Tightly coupled to physical world Embed numerous distributed devices to monitor and interact with physical world Networked devices that coordinate and perform higher-level tasks Exploit spatially and temporally dense, in situ, sensing and actuation
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CSE 466 - Winter 2008 Wireless Sensor Networks 1 · 1 CSE 466 - Winter 2008 Wireless Sensor Networks 1 Wireless Sensor Networks Important trend in embedded computing Connecting the
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CSE 466 - Winter 2008 Wireless Sensor Networks 1
Wireless Sensor Networks
Important trend in embedded computingConnecting the physical world to the world of information
Sensing (e.g., sensors)Actuation (e.g., robotics)
Wireless sensor networks are enabled by three trends:Cheaper computation (Moore’s Law)Compact sensing (MEMS sensors)Wireless networking (low-power radios)
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What is embedded networked sensing?
Embedded Networked
Sensing
Control system w/small-form factoruntethered nodes
Exploitcollaborativesensing and action
Tightly coupled to physical world
Embed numerous distributed devices to monitor and interact with physical world
Networked devices that coordinate and
perform higher-level tasks
Exploit spatially and temporally dense, in situ, sensing and actuation
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Wireless sensor networks
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Low resolution Sensor, Test4, Increasing frequency
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The Basic Idea
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Applications
Untethered micro sensors will go anywhere and measure anything – traffic flow, water level, number of people walking by, temperature. This is developing into something like a nervous system for the earth.
Horst Stormer in Business Week, 8/23-30, 1999.Applications
Environmental sensingHabitat monitoringPrecision agricultureMilitary operationsCondition-based maintenanceHealth care
Range and connectivityLocalization and synchronizationRouting protocolsPower managementComputation
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Range and Connectivity
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Range and Connectivity (cont’d)
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Range and Connectivity
How do sensor nodes discover their neighbors?Transitively, who can their neighbors talk to?
What radio range to use?Smaller, less power, more bandwidth (less interference)Larger, more power, more interference
What to do when nodes are really close together?Let one handle region and others sleep?
What happens when there are isolated islands?Use mobile nodes?Add more nodes?
Vary transmit power?Adjust to situation?
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Localization and Synchronization
Node location is important knowledgeMake decisions about which are active and which sleep
Need synchronized clocksKnow the time an event is observed at each of multiple nodes
Spatial signal processingDetermine location of sensed phenomenaNeed to know relative locations for triangulationNeed to know time for time-of-arrival calculations
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Routing Protocols
Getting data from one point to anotherReliability of communicationBest effort or acknowledgements with retransmit
Which nodes forward dataIf all, then may saturate available bandwidthIf not enough, may not get to where it needs to go
Adjust as nodes are added/removedNumber of hops per packet
Loss at each hopPower for each hop
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Routing Protocols
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Power Management
Maximize lifetime of nodeIndependent power managementRendezvous for communication
make sure both awake at same time
Maximize lifetime of networkJudiciously choose which nodes sleepWakeup to fill in for others that run out of power
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Computation
How is data processed?In network – more computationAt edges, after it is gathered – more communication
How much aggregation is done?Summary data vs. raw data
Pushing new computation into networkSecurity concerns
Collaborative signal processingMultiple nodes working together
Where is data stored?Can I “google” the real world?
What is the programming model?
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Application: Environmental Sensing
Tracking a chemical cloudEmergency responseSprinkle sensors overaffected area and vicinityTrack movement of cloud and warn affected communities
F. Zhao
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Application: Habitat Monitoring
Great Duck Island, MEMonitoring burrow nest and environment of petrelsData previously unavailable
Much too expensive to gather
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Application: Precision Agriculture
Monitor micro-climates throughout vineyardAdd water, heat, and fertilizer where neededCost-savings, maximum yield, customize grape
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Application: Military Operations
Sniper detectionVehicle tracking
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Application: Condition-based Maintenance
Monitor structural stressesData collection from vehicle driving byEarly warning of problems
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Application: Health Care
Monitor all aspects of human activityMechanics/chemistry of bodyTrends over timeDetect problems earlyMonitor effects of medicationElder care
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Sensor networks are the next IT revolution
year
log
(peo
ple
per c
ompu
ter)
Streaming informationto/from physical world
Number crunchingData storage
Personalproductivityinteractive
Ultimately used in many ways not previously imagined!
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A Popular Sensor Network Platform
UC Berkeley sensor “mote”ATmega 8-bit microcontroller40Kb/sec radio (433MHz)128K code, 4KB data
Mainstay platform for the sensor network researchcommunityUsed in CSE466 in the past(2003-2006)Three main form factors
Mica2DotTelos
Now distributed by Crossbow (xbow.com)
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Platform details
ATmega microcontroller (103L, 128) or TI MSP430 (Telos)32Khz crystal and 4Mhz crystal
10 bit ADC2 UARTsSPI busI2C busRadio (RFM or Chipcon 1000)
External serial flash memory (512K byte)Connectors for interfacing to sensor and programming boards3 programmable leds (1 for dot) JTAG programming port
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Key Design Elements
Efficient wireless protocol primitivesFlexible sensor interfaceUltra-low power standbyVery fast wakeupWatchdog and monitoringData SRAM is critical limiting resource
proc
DataSRAM pgm
EPROM
timersSensor Interface digital sensors
analog sensorsADC
Wireless NetInterface
Wired NetInterface
RFtransceiver
antenna
serial linkUSB,RS-232
Low-powerStandby & Wakeup
Flash Storage
pgm images
data logs
WD
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Mote Platform Evolution
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Sensors
Add-on boards from Crossbow
Add-on boards by researchersUltrasound (MIT), RFID reader (UW), etc. dot
mag ultrasound
acoustic
ProtoypingMica2DotMDA300CA
Weatherboards Mica2DotNot released:
GPS weatherboardMica2MTS400/420
On board humidity/temp. External sensors.Mica2MDA300CA
PrototypingMica2DotMTS500CA
Light, Temperature, Acoustic, Sounder, 2-Axis Accelerometer (ADXL202), and 2-Axis Magnetometer
Mica2MTS300CA
Light (photo resistor)Temperature (Thermistor)Prototyping area
Mica2MTS101CA
SensorsMote SupportPart #
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MTS101CA
Light photo resistor-Clairex CL94L Thermistor - YSI 44006Both sensor are highly non-linearGood prototyping area
Real time control of vehicle dynamics3 bridge accelerometers (500g-1000g) mounted in tireSensor board has 3 channels of amplifiers, filters, programmable D/As for bridge balancingMonitor and analyzed acceleration forces when tire is in contact with groundTransmit results every revolution3 motes, 1 master, 2 slaves
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COTS-BOTS (UCB)
5” x 2.5” x 3” size<$250 total2-axis accelerometer
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Robomote (USC)Less than 0.000047m3
$150 eachPlatform to test algorithms for adaptive wireless networks with autonomous robots
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Enclosures for Environmental Monitoring
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A newer platform – the Intel iMote2
Developed by Intel Research- 13-416MHz 32-bit PXA271 - 64MB memory (half Flash, half RAM)- IEEE 802.15.4 radio- 250 kbits/sec (2.4GHz)New for CSE466 since last yearRecently available commercially- again from Crossbow (xbox.com)
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Platform details
Intel PXA271 XScale® at 13 – 416MHzIntel Wireless MMX DSP Coprocessor256kB SRAM, 32MB FLASH, 32MB SDRAMIntegrated 802.15.4 Radio and 2.4GHz Antenna,Multi-color Status Indicator LEDUSB Client With On-board mini-BConnector and Host AdaptersRich Set of Standard I/O: 3xUART, 2xSPI, I2C, SDIO, GPIOsApplication Specific I/O: I2S, AC97, Camera Chip Interface, JTAGCompact Size: 36mm x 48mm x 9mm, 12g (w/o battery)
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iMote2 Connectors
UARTs, SPI, I2CUSBHigh-speeddata transfer(up to 192Mbps)JTAGSDIOCameraPower
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Other iMote2 elements
Battery board (51g – 3 AAA)4x weight and 2x volume of main board
Interface boardExpands USB ports and provides JTAG interface (up to 1MB/sec per port)
Basic sensor board5 sensors for basic applications
Other boardsIntel, UW, UCLA, Yale
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More detail
In CSE466, we’ll use the iMote2 base board and basicsensor board
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iMote2 Basic Sensor Board
ST Micro LIS3L02DQ 3D 12-bit 2g accelerometerHigh Accuracy, +/-.3°C Sensirion SHT15 temperature/humidity sensorTAOS TSL2651 light sensorTI Tmp175 digital temperaturesensor with two-wire interfaceMaxim MAX1363 4-channel general-purpose A/D