Wsn handbook
- 1. Wireless sensor networks Dr. Narmada Alaparthi
- 2. 2 Wireless sensor networks A sensor node (mote) 8K RAM, 4Mhz processor magnetism, heat, sound, vibration, infrared wireless (radio broadcast) communication up to 100 feet costs ~$10 (right now costs $200)
- 3. 3 New Class of Computing year log(peoplepercomputer) streaming information to/from physical world Number Crunching Data Storage productivity interactive Mainframe Minicomputer Workstation PC Laptop PDA
- 4. 4 Why use a WSN? • Ease of deployment Wireless communication means no need for a communication infrastructure setup Drop and play • Low-cost of deployment Nodes are built using off-the-shelf cheap components • Fine grain monitoring Feasible to deploy nodes densely for fine grain monitoring
- 5. 5 Challenges in sensor networks • Energy constraint • Unreliable communication • Unreliable sensors • Ad hoc deployment • Large scale networks • Limited computation power • Distributed execution : Nodes are battery powered : Radio broadcast, limited bandwidth, bursty traffic : False positives : Pre-configuration inapplicable : Algorithms should scale well : Centralized algorithms inapplicable : Difficult to debug & get it right
- 6. 6 Outline • Applications • Platforms (hw&sw) • WSN services (layers? what layers?) • Comparison with the Internet architecture
- 7. 7 • Monitoring nesting behavior of birds Great Ducks experiment • Detecting forest fires • Detecting chemical or biological attacks • Monitoring Redwood trees Ecology monitoring
- 8. 8 Dense Self-Organized Multihop Network
- 9. 9R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R 8 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 Temperature vs. Time Temperature(C) Humidity vs. Time 35 45 55 65 75 85 95 RelHumidity(%) 101 104 109 110 111 2003, unpublished Bottom Top 36m 34m 30m 20m 10m
- 10. 10 Precision agriculture • Wireless sensor networks can be placed on farm lands to monitor temperature, humidity, fertilizer and pesticide levels • Pesticide and fertilizer can only be applied when and where required Pesticide and fertilizer per one acre costs $20 Considering 100,000 acres savings of $2 million possible Vineyards BC
- 11. 11 Equipment Health Monitoring in Semiconductor Fab Fab Equipment Mote + Vibration Sensors Ad Hoc Mote Network Intranet 802.11 Mesh Intranet isolation Root Node • Equipment failures in production fabs is very costly Predict and perform preemptive maintenance • Typical fab has ~5,000 vibration sensors Pumps, scrubbers, … Electricians collect data by hand few times a year Sample: 10’s kilohertz, high precision, few seconds
- 12. 12 Put tripwires anywhere—in deserts, other areas where physical terrain does not constrain troop or vehicle movement—to detect, classify & track intruders Project ExScal: Concept of operation
- 13. 13 Envisioned ExScal customer application Gas pipeline Border control Canopy precludes aerial techniques Rain forest – mountains – water environmental challenges Convoy protection IED Hide Site Detect anomalous activity along roadside
- 14. 14 ExScal summary • Application has tight constraints of event detection scenarios: long life but still low latency, high accuracy over large perimeter area • Demonstrated in December 2004 in Florida • Deployment area: 1,260m x 288m • ~1000 XSMs, the largest WSN • ~200 XSSs, the largest 802.11b ad hoc network
- 15. 15 Line in the sand project • Thick line allows detection & classification as intruders enter the protected region; also allows fine grain intruder localization • Grid of thin lines allows bounded uncertainty tracking Thick Entry Line A S S E T 1 km 250 m
- 16. 16 ExScal sample scenarios Intruding person walks through thick line • (pir) detection, classification, and fine-grain localization Intruding vehicle enters perimeter and crosses thick line • (acoustic) detection, classification, and fine-grain localization Person/ATV traverses through the lines • coarse-grain tracking Management operations to control signal chains, change parameters, and programs dynamically; query status and execute commands
- 17. WSN Platforms: Hardware & Software
- 18. 18 Types of sensor platforms 1. RFID equipped sensors 1. Smart-dust tags typically act as data-collectors or “trip-wires” limited processing and communications • Mote/Stargate-scale nodes • more flexible processing and communications 1. More powerful gateway nodes, potentially using wall power
- 19. 19 Grain-sized nodes Powered by inductive coupling to a transmission from a reader device to transmit a message back Available commercially at very low prices × Computation power is severely limited × Can only trasmit stored unique id and variable × Hard to add any interesting sensing capability
- 20. 20 Matchbox-sized nodes • Mica series, XSM node, Telos • 8-bit microprocessor, 4MHz CPU ATMEGA 128, ATMEL 8535, or Motorola HCS08 • ~4Kb RAM holds run-time state (values of the variables) of the program • ~128Kb programmable Flash memory holds the application program Downloaded via a programmer-board or wirelessly • Additional Flash memory storage space up to 512Kb.
- 21. 21 Mica2 and Mica2Dot • ATmega128 CPU – Self-programming • Chipcon CC1000 – FSK – Manchester encoding – Tunable frequency • Low power consumption – 2 AA battery = 3V 1 inch
- 22. 22 Basic Sensor Board • Light (Photo) • Temperature • Prototyping space for new hardware designs
- 23. 23 Mica Sensor Board • Light (Photo) • Temperature • Acceleration – 2 axis – Resolution: ±2mg • Magnetometer – Resolution: 134µG • Microphone • Tone Detector • Sounder – 4.5kHz
- 24. 24 Telos Platform • Low Power Minimal port leakage Hardware isolation and buffering • Robust Hardware flash write protection Integrated antenna (50m-125m) Standard IDC connectors • Standards Based USB IEEE 802.15.4 (CC2420 radio) • High Performance 10kB RAM, 16-bit core, extensive double buffering 12-bit ADC and DAC (200ksamples/sec) DMA transfers while CPU off
- 25. 25 Brick-sized node: Stargate • Mini Linux computers communicating via 802.11 radios Computationally powerful High bandwidth Requires more energy (AA infeasible) • Used as a gateway between the Internet and WSN
- 26. 26 Stargate
- 27. 27 Outline • Hardware RFID, Spec Mica2, XSM, Telos Stargate • Software TinyOS
- 28. 28 TinyOS • most popular operating system for WSN developed by UC Berkeley • features a component-based architecture software is written in modular pieces called components Each component denotes the interfaces that it provides An interface declares a set of functions called commands that the interface provider implements and another set of functions called events that the interface user should be ready to handle • Easy to link components together by “wiring” their interfaces to form larger components similar to using Lego blocks
- 29. 29 TinyOS • provides a component library that includes network protocols, services, and sensor drivers • An application consists of a component written by the application developer and the library components that are used by the components in (1) • An application developer writes only the application component that describes the sensors used in the application, the middleware services configured with the appropriate parameters based on the needs of the application
- 30. 30 Benefits of using TinyOS • Separation of concerns TinyOS provides a proper networking stack for wireless communication that abstracts away the underlying problems and complexity of message transfer from the application developer E.g., MAC layer • Concurrency control TinyOS provides a scheduler that achieves efficient concurrency control An interrupt-driven execution model is needed to achieve a quick response time for the events and capture the data For example, a message transmission may take up to 100msec, and without an interrupt-driven approach the node would miss sensing and processing of interesting data in this period Scheduler takes care of the intricacies of interrupt-driven execution and provides concurrency in a safe manner by scheduling the execution in small threads.
- 31. 31 Benefits of TinyOS • Modularity TinyOS’s component model facilitates reuse and reconfigurability since software is written in small functional modules. Several middleware services are available as well-documented components Over 500 research groups and companies are using TinyOS and numerous groups are actively contributing code to the public domain
- 32. 32 RadioTimingSecDedEncode The Complete Application RadioCRCPacket UART UARTnoCRCPacket ADC phototemp AMStandard ClockC bitbytepacket SenseToRfm HW SW IntToRfm MicaHighSpeedRadioM RandomLFSRSPIByteFIFO SlavePin noCRCPacket Timer photo ChannelMon generic comm CRCfilter
- 33. 33 TOS Execution Model • commands request action ack/nack at every boundary call command or post task • events notify occurrence HW interrupt at lowest level may signal events call commands post tasks • tasks provide logical concurrency preempted by events RFM Radio byte Radio Packet bitbytepacket event-driven bit-pump event-driven byte-pump event-driven packet-pump message-event driven active message application comp encode/decode crc data processing
- 34. 34 Event-Driven Sensor Access Pattern • clock event handler initiates data collection • sensor signals data ready event • data event handler calls output command • device sleeps or handles other activity while waiting • conservative send/ack at component boundary command result_t StdControl.start() { return call Timer.start(TIMER_REPEAT, 200); } event result_t Timer.fired() { return call sensor.getData(); } event result_t sensor.dataReady(uint16_t data) { display(data) return SUCCESS; } SENSE Timer Photo LED
- 35. 35 Programming Syntax • TinyOS 2.0 is written in an extension of C, called nesC • Applications are too just additional components composed with OS components • Provides syntax for TinyOS concurrency and storage model commands, events, tasks local frame variable • Compositional support separation of definition and linkage robustness through narrow interfaces and reuse Interpositioning • Whole system analysis and optimization
- 36. WSN Services:
- 37. 37 WSN services • MAC protocols (BMAC, SMAC, TMAC, etc.) • Topology control (GAF, SPAN, CEC, etc.) • Clustering (Leach, FLOC, etc.) • Time synchronization (Flooding time sync, reference broadcast) • Localization (cricket, range-free techniques...) • Routing (convergecast tree, geographic routing, hierarchical...) • Querying (DSIB, DQT, directed diffusion, etc.) • Tracking (Stalk, Trail, etc.) • Network reprogramming
- 39. 39 Compared to Internet • No clear layering; cross layer design is norm • No separation between edge vs core of the network all nodes are both routers and hosts • End-to-end principle fails unreliable channels, multihop latency • Ad hoc deployment timesync, localization, topology control, clustering etc services needed • Routing needs are different...
Editor's Notes
- #14: (no notes)