1CS 525 Advanced Topics in Distributed SystemsSpring 08Indranil GuptaLecture 4Introduction to Sensor NetworksJanuary 24, 2008A Gram of Gold=How Many Processors?• Smallest state-of-the-art transistor today is made of a single Gold atom– Still in research, not yet in industry.• Pentium P4 contains 42 M transistors• Gold atomic weight is 196 ~ 200. • 1 g of Au contains 3 X 10^21 atoms => 7.5 X 10^18 P4 processors from a gram of Au => 1 billion P4’s per personSensor Networks Hype, But do we really need this technology?• Coal mines have always had CO/CO2 sensors• Industry has used sensors for a long timeToday…• Excessive Information– Environmentalists collecting data on an island– Army needs to know about enemy troop deployments– Humans in society face information overload• Sensor Networking technology can help filter and process this information (And then perhaps respond automatically?)Growth of a technology requiresI. HardwareII. Operating Systems and ProtocolsIII. Killer applications– Military and CivilianSensor Nodes• Motivating factors for emergence: applications, Moore’s Law, wireless comm., MEMS (micro electro mechanical sensors)• Canonical Sensor Node contains1. Sensor(s) to convert a different energy form to an electrical impulse e.g., to measure temperature2. Microprocessor3. Communications link e.g., wireless4. Power source e.g., batteryLaser diodeIII-V processPassive CCR comm.MEMS/polysiliconSensorMEMS/bulk, surface, ...Analog I/O, DSP, ControlCOTS CMOSSolar cellCMOS or III-VThick film batterySol/gel V2O5Power capacitorMulti-layer ceramic1-2 mmExample: Berkeley “Motes” or “Smart Dust”Can you identify the 4 components here?2Example Hardware• Size– Golem Dust: 11.7 cu. mm– MICA motes: Few inches• Everything on one chip: micro-everything– processor, transceiver, battery, sensors, memory, bus– MICA: 4 MHz, 40 Kbps, 4 KB SRAM / 512 KB Serial Flash, lasts 7 days at full blast on 2 x AA batteriesExamplesSpec, 3/03• 4 KB RAM• 4 MHz clock• 19.2 Kbps, 40 feet• Supposedly $0.30MICA: Current State of the Art (xbow)Similar i-motes by IntelTypes of Sensors• Micro-sensors (MEMS, Materials, Circuits)– acceleration, vibration, gyroscope, tilt, magnetic, heat, motion, pressure, temp, light, moisture, humidity, barometric, sound• Chemical– CO, CO2, radon• Biological– pathogen detectors• [Actuators too (mirrors, motors, smart surfaces, micro-robots) ]I2C bus – simple technology• Inter-IC connect– e.g., connect sensor to microprocessor• Simple features– Has only 2 wires – Bi-directional– serial data (SDA) and serial clock (SCL) bus • Up to 3.4 Mbps• Developed By PhilipsTransmission Medium• Spec, MICA: Radio Frequency (RF)– Broadcast medium, routing is “store and forward”, links are bidirectional• Smart Dust : smaller size but RF needs high frequency => higher power consumptionOptical transmission: simpler hardware, lower power– Directional antennas only, broadcast costly– Line of sight required– Switching links costly : mechanical antenna movements– Passive transmission (reflectors) => wormhole routing– Unidirectional linksBerkeley Family of Motes3Summary: Sensor Node• Small Size : few mm to a few inches• Limited processing and communication– MhZ clock, MB flash, KB RAM, 100’s Kbps (wireless) bandwidth• Limited power (MICA: 7-10 days at full blast)• Failure prone nodes and links (due to deployment, fab, wireless medium, etc.)• But easy to manufacture and deploy in large numbers• Need to offset this with scalable and fault-tolerant OS’s and protocolsSensor-node Operating SystemIssues– Size of code and run-time memory footprint• Embedded System OS’s inapplicable: need hundreds of KB ROM– Workload characteristics• Continuous ? Bursty ?– Application diversity• Want to reuse sensor nodes– Tasks and processes• Scheduling• Hard and soft real-time– Power consumption– Communication TinyOS design point– Bursty dataflow-driven computations– Multiple data streams => concurrency-intensive– Real-time computations (hard and soft)– Power conservation– Size– Accommodate diverse set of applications TinyOS: – Event-driven execution (reactive mote)– Modular structure (components) and clean interfacesProgramming TinyOS• Use a variant of C called NesC• NesC defines components• A component is either – A module specifying a set of methods and internal storage (~like a Java static class)A module corresponds to either a hardware element on the chip (e.g., the clock or the LED), or to a user-defined software moduleModules implement and use interfaces– Or a configuration , a set of other components wired together by specifying the unimplemented methods invocation mappings• A complete NesC application then consists of one top level configurationA Complete TinyOS ApplicationRFMRadio byteRadio Packeti2cTempphotoMessaging LayerclocksbitbytepacketRouting Layersensing applicationapplicationHWSWADCmessagingroutingTinyOS component model• Component specifies:• Component invocation is event driven, arising from hardware events• Static allocation only avoids run-time overhead• Scheduling: dynamic, hard (or soft) real-time• Explicit interfaces accommodate different applicationsInternal StateInternal TasksCommands Events4Steps in writing and installing your NesC app(applies to MICA Mote)• On your PC– Write NesC program – Compile to an executable for the mote– Plug the mote into the parallel port through a connector board– Install the program• On the mote– Turn the mote on, and it’s already running your application TinyOS Facts• Software Footprint 3.4 KB • Power Consumption on Rene PlatformTransmission Cost: 1 µJ/bitInactive State: 5 µAPeak Load: 20 mA• Concurrency support: at peak load CPU is asleep 50% of time• Events propagate through stack <40 µSEnergy – a critical resource• Power saving modes:– MICA: active, idle, sleep• Tremendous variance in energy supply and demand– Sources: batteries, solar, vibration, AC– Requirements: long term deployment v. short term deployment, bandwidth intensiveness– 1 year on 2xAA batteries => 200 uA average current Energy – a critical resource0.126 mA10 ms2000 HzThermistor0.170 mA200 ms2000 HzThermopile0.775 mA500 ms500 HzHumidity0.010 mA500 ms10 HzPress Temp0.010 mA500 ms10 HzPressure0.150 mA500 ms2 HzI2C Temp1.235 mA10 ms2000 HzPhoto3.6 mA30 ms40 kHzRadio
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