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Mobile and Pervasive Computing - 4 Location in Pervasive Computing

Shwetak N. Patel, University of Washington http://shwetak.com. Mobile and Pervasive Computing - 4 Location in Pervasive Computing. Presented by: Dr. Adeel Akram University of Engineering and Technology, Taxila,Pakistan http://web.uettaxila.edu.pk/CMS/SP2014/teMPCms. Outline.

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Mobile and Pervasive Computing - 4 Location in Pervasive Computing

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  1. Shwetak N. Patel, University of Washington http://shwetak.com Mobile and Pervasive Computing - 4Location in Pervasive Computing Presented by: Dr. Adeel Akram University of Engineering and Technology, Taxila,Pakistan http://web.uettaxila.edu.pk/CMS/SP2014/teMPCms

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

  3. 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

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

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

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

  27. Active Badge • IR-based • Proximity

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

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

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

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

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

  33. Place Lab http://research.microsoft.com/apps/pubs/default.aspx?id=64611 • “Beacons in the wild” • WiFi, Bluetooth, GSM, etc • Community authored databases • API for a variety of platforms • RightSPOT (MSR) – FM towers • http://msr-waypoint.com/en-us/um/people/jckrumm/Publications%202003/rightSPOT%20publish.pdf

  34. 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)

  35. 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, AT&T), WiFi (RADAR, Ekahau, Place Lab), FM (MSR)

  36. 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)

  37. Beacon-based localization

  38. Wifi localization (ex. Ekahau) http://www.ekahau.com/

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

  40. PowerLine Positioning http://ubicomplab.cs.washington.edu/wiki/PLP • Indoor localization using standard household power lines

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

  42. Signal Map 1st Floor 2nd Floor

  43. Example

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

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

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

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

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

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

  50. Questions???

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