1 / 48

Location in Pervasive Computing

Location in Pervasive Computing. Shwetak N. Patel University of Washington More info: shwetak.com Special thanks to Alex Varshavsky and Gaetano Borriello for their contribution to this content. design:. use:. ubi comp lab. build:. university of washington. university of washington.

sylvie
Download Presentation

Location in Pervasive Computing

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Location in Pervasive Computing Shwetak N. PatelUniversity of Washington More info: shwetak.com Special thanks to Alex Varshavsky and Gaetano Borriello for their contribution to this content design: use: ubicomp lab build: university of washington university of washington Computer Science & Engineering Electrical Engineering

  2. Location • A form of contextual information • Person’s physical position • Location of a device • Device is a proxy of a person’s location • Used to help derive activity information

  3. Location • Well studied topic (3,000+ PhD theses??) • Application dependent • Research areas • Technology • Algorithms and data analysis • Visualization • Evaluation

  4. Location Tracking

  5. Representing Location Information • Absolute • Geographic coordinates (Lat: 33.98333, Long: -86.22444) • Relative • 1 block north of the main building • Symbolic • High-level description • Home, bedroom, work

  6. No one size fits all! • Accurate • Low-cost • Easy-to-deploy • Ubiquitous • Application needs determine technology

  7. Consider for example… • Motion capture • Car navigation system • Finding a lost object • Weather information • Printing a document

  8. Others aspects of location information • Indoor vs. outdoor • Absolute vs. relative • Representation of uncertainty • Privacy model

  9. WiFi Beacons Ad hoc signal strength GPS Physical contact VHF Omni Ranging Ultrasonic time of flight Laser range-finding Array microphone Infrared proximity Stereo camera E-911 Lots of technologies! Ultrasound Floor pressure

  10. Some outdoor applications E-911 Bus view Car Navigation Child tracking

  11. Some indoor applications Elder care

  12. Outline • Defining location • Methods for determining location • Ex. Triangulation, trilateration, etc. • Systems • Challenges and Design Decisions • Considerations

  13. Approaches for determining location • Localization algorithms • Proximity • Lateration • Hyperbolic Lateration • Angulation • Fingerprinting • Distance estimates • Time of Flight • Signal Strength Attenuation

  14. Proximity • Simplest positioning technique • Closeness to a reference point • Based on loudness, physical contact, etc

  15. Lateration • Measure distance between device and reference points • 3 reference points needed for 2D and 4 for 3D

  16. Hyperbolic Lateration • Time difference of arrival (TDOA) • Signal restricted to a hyperbola

  17. Angulation • Angle of the signals • Directional antennas are usually needed

  18. Determining Distance • Time of flight • Speed of light or sound • Signal strength • Known drop off characteristics 1/r^2-1/r^6 • Problems: Multipath

  19. Fingerprinting • Mapping solution • Address problems with multipath • Better than modeling complex RF propagation pattern

  20. Fingerprinting

  21. Fingerprinting • Easier than modeling • Requires a dense site survey • Usually better for symbolic localization • Spatial differentiability • Temporal stability

  22. Reporting Error • Precision vs. Accuracy

  23. Reporting Error • Cumulative distribution function (CDF) • Absolute location tracking systems • Accuracy value and/or confusion matrix • Symbolic systems

  24. Location Systems • Distinguished by their underlying signaling system • IR, RF, Ultrasonic, Vision, Audio, etc

  25. GPS • Use 24 satellites • TDOA • Hyperbolic lateration • Civilian GPS • L1 (1575 MHZ) • 10 meter acc.

  26. Active Badge • IR-based • Proximity

  27. Active Bat • Ultrasonic • Time of flight of ultrasonic pings • 3cm resolution

  28. Cricket • Similar to Active Bat • Decentralized compared to Active Bat

  29. Cricket vs Active Bat • Privacy preserving • Scaling • Client costs Active Bat Cricket

  30. Ubisense • Ultra-wideband (UWB) 6-8 GHz • Time difference of arrival (TDOA) and Angle of arrival (AOA) • 15-30 cm

  31. RADAR • WiFi-based localization • Reduce need for new infrastructure • Fingerprinting

  32. Place Lab • “Beacons in the wild” • WiFi, Bluetooth, GSM, etc • Community authored databases • API for a variety of platforms • RightSPOT (MSR) – FM towers

  33. ROSUM • Digital TV signals • Much stronger signals, well-placed cell towers, coverage over large range • Requires TV signal receiver in each device • Trilateration, 10-20m (worse where there are fewer transmitters)

  34. Comparing Approaches • Many types of solutions (both research and commercial) • Install custom beacons in the environment • Ultra-wideband (Ubisense), Ultrasonic (MIT Cricket, Active Bat), Bluetooth • Use existing infrastructure • GSM (Intel, Toronto), WiFi (RADAR, Ekahau, Place Lab), FM (MSR)

  35. Limitations • Beacon-based solutions • Requires the deployment of many devices (typically at least one per room) • Maintenance • Using existing infrastructure • WiFi and GSM • Not always dense near some residential areas • Little control over infrastructure (especially GSM)

  36. Beacon-based localization

  37. Wifi localization (ex. Ekahau)

  38. Tower IDs and signals change over time! • GSM localization Coverage?

  39. PowerLine Positioning • Indoor localization using standard household power lines

  40. Signal Detection • A tag detects these signals radiating from the electrical wiring at a given location

  41. Signal Map 1st Floor 2nd Floor

  42. Example

  43. Passive location tracking • No need to carry a tag or device • Hard to determine the identity of the person • Requires more infrastructure (potentially)

  44. Active Floor • Instrument floor with load sensors • Footsteps and gait detection

  45. Motion Detectors • Low-cost • Low-resolution

  46. Computer Vision • Leverage existing infrastructure • Requires significant communication and computational resources • CCTV

  47. Other systems? • Inertial sensing • HVACs • Ambient RF • etc.

  48. Considerations • Location type • Resolution/Accuracy • Infrastructure requirements • Data storage (local or central) • System type (active, passive) • Signaling system

More Related