1. Wireless sensor networks Murat Demirbas

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 (people per computer)‏ streaming information to/from physical world Number Crunching Data Storage productivity interactive Mainframe Minicomputer WorkstationPCLaptop 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9. 9 2003, unpublished Bottom Top 36m 34m 30m 20m 10m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-programmingSelf-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: 134G 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 softwareis 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 RadioTiming SecDedEncode The Complete Application RadioCRCPacket UART UARTnoCRCPacket ADC phototemp AMStandard ClockC bit byte packet 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 bit byte packet 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

38. Comparison to Internet architecture:

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...