1. Mobile and Pervasive Computing - 4 Location in Pervasive Computing
Shwetak N. Patel, University of Washington
Mobile and Pervasive Computing - 4 Location in Pervasive Computing
Presented by: Dr. Adeel Akram
University of Engineering and Technology, Taxila,Pakistan

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

10. Some outdoor applications
Bus view
Car Navigation
Child tracking

11. Some indoor applications
Elder care

12. Outline Defining location Methods for determining location Systems
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 Signal strength
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. Signal Strength (RSSI)
Fingerprinting
SSID (Name)
BSSID (MAC address)
Signal Strength (RSSI)
linksys
00:0F:66:2A:61:00 18
starbucks
00:0F:C8:00:15:13 15
newark wifi
00:06:25:98:7A:0C 23

21. Fingerprinting Easier than modeling Requires a dense site survey
Usually better for symbolic localization

22. Reporting Error
Precision vs. Accuracy

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

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

25. GPS Uses 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” Community authored databases
“Beacons in the wild”
WiFi, Bluetooth, GSM, etc
Community authored databases
API for a variety of platforms
RightSPOT (MSR) – FM towers
us/um/people/jckrumm/Publications%202003/rightSPOT%20publish.pdf
RightSPOT uses a vector of radio signal strengths taken from different frequencies to identify location. Each time a location is to be inferred, the device scans through a set of FM frequencies and records the signal strength of each one.
A standard SPOT device must be able to scan FM radio stations and measure signal strength in order to find a sufficiently powerful one transmitting SPOT data.

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)
Devices equipped with Rosum positioning technology will be able to access a host of location-based applications that can only be made possible with reliable, accurate positioning in areas where most mobile device users spend most of their time -- indoors and in urban areas. Instead of using GPS satellites as beacon platforms, Rosum uses existing, land-based broadcast television antennas.
However the downside is, Rosum doesn't work where there's absolutely no TV signal, like in a mountain valley or the middle of an ocean.

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

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

36. Challenges and Design Considerations
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)

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

40. PowerLine Positioning
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 nd 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. Outline Defining location Methods for determining location
Ex. Triangulation, trilateration, etc.
Location Systems
Challenges and Design Decisions
Considerations

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

50. Questions???

51. References
Special thanks to Alex Varshavsky and Gaetano Borriello for their contribution to this content

52. Assignment #3
Write Short Notes on any 5 of the ubiquitous computing projects at edu/projects