Location in pervasive computing
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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.

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Location in pervasive computing l.jpg

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



ubicomp lab


university of washington

university of washington

Computer Science & Engineering

Electrical Engineering

Location l.jpg

  • 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

Location3 l.jpg

  • Well studied topic (3,000+ PhD theses??)

  • Application dependent

  • Research areas

    • Technology

    • Algorithms and data analysis

    • Visualization

    • Evaluation

Representing location information l.jpg
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

No one size fits all l.jpg
No one size fits all!

  • Accurate

  • Low-cost

  • Easy-to-deploy

  • Ubiquitous

  • Application needs determine technology

Consider for example l.jpg
Consider for example…

  • Motion capture

  • Car navigation system

  • Finding a lost object

  • Weather information

  • Printing a document

Others aspects of location information l.jpg
Others aspects of location information

  • Indoor vs. outdoor

  • Absolute vs. relative

  • Representation of uncertainty

  • Privacy model

Lots of technologies l.jpg

WiFi Beacons

Ad hoc signal strength


Physical contact

VHF Omni Ranging

Ultrasonic time of flight

Laser range-finding

Array microphone

Infrared proximity

Stereo camera


Lots of technologies!


Floor pressure

Some outdoor applications l.jpg
Some outdoor applications


Bus view

Car Navigation

Child tracking

Outline l.jpg

  • Defining location

  • Methods for determining location

    • Ex. Triangulation, trilateration, etc.

  • Systems

  • Challenges and Design Decisions

  • Considerations

Approaches for determining location l.jpg
Approaches for determining location

  • Localization algorithms

    • Proximity

    • Lateration

    • Hyperbolic Lateration

    • Angulation

    • Fingerprinting

  • Distance estimates

    • Time of Flight

    • Signal Strength Attenuation

Proximity l.jpg

  • Simplest positioning technique

  • Closeness to a reference point

  • Based on loudness, physical contact, etc

Lateration l.jpg

  • Measure distance between device and reference points

  • 3 reference points needed for 2D and 4 for 3D

Hyperbolic lateration l.jpg
Hyperbolic Lateration

  • Time difference of arrival (TDOA)

  • Signal restricted to a hyperbola

Angulation l.jpg

  • Angle of the signals

  • Directional antennas are usually needed

Determining distance l.jpg
Determining Distance

  • Time of flight

    • Speed of light or sound

  • Signal strength

    • Known drop off characteristics 1/r^2-1/r^6

  • Problems: Multipath

Fingerprinting l.jpg

  • Mapping solution

  • Address problems with multipath

  • Better than modeling complex RF propagation pattern

Fingerprinting21 l.jpg

  • Easier than modeling

  • Requires a dense site survey

  • Usually better for symbolic localization

  • Spatial differentiability

  • Temporal stability

Reporting error l.jpg
Reporting Error

  • Precision vs. Accuracy

Reporting error23 l.jpg
Reporting Error

  • Cumulative distribution function (CDF)

    • Absolute location tracking systems

  • Accuracy value and/or confusion matrix

    • Symbolic systems

Location systems l.jpg
Location Systems

  • Distinguished by their underlying signaling system

    • IR, RF, Ultrasonic, Vision, Audio, etc

Slide25 l.jpg

  • Use 24 satellites

  • TDOA

  • Hyperbolic lateration

  • Civilian GPS

    • L1 (1575 MHZ)

      • 10 meter acc.

Active badge l.jpg
Active Badge

  • IR-based

  • Proximity

Active bat l.jpg
Active Bat

  • Ultrasonic

  • Time of flight of ultrasonic pings

  • 3cm resolution

Cricket l.jpg

  • Similar to Active Bat

  • Decentralized compared to Active Bat

Cricket vs active bat l.jpg
Cricket vs Active Bat

  • Privacy preserving

  • Scaling

  • Client costs

Active Bat Cricket

Ubisense l.jpg

  • Ultra-wideband (UWB) 6-8 GHz

  • Time difference of arrival (TDOA) and Angle of arrival (AOA)

  • 15-30 cm

Radar l.jpg

  • WiFi-based localization

  • Reduce need for new infrastructure

  • Fingerprinting

Place lab l.jpg
Place Lab

  • “Beacons in the wild”

    • WiFi, Bluetooth, GSM, etc

  • Community authored databases

  • API for a variety of platforms

  • RightSPOT (MSR) – FM towers

Rosum l.jpg

  • 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)

Comparing approaches l.jpg
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)

Limitations l.jpg

  • 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)

Slide38 l.jpg

Tower IDs and signals change over time!

  • GSM localization


Powerline positioning l.jpg
PowerLine Positioning

  • Indoor localization using standard household power lines

Signal detection l.jpg
Signal Detection

  • A tag detects these signals radiating from the electrical wiring at a given location

Signal map l.jpg
Signal Map

1st Floor 2nd Floor

Passive location tracking l.jpg
Passive location tracking

  • No need to carry a tag or device

    • Hard to determine the identity of the person

  • Requires more infrastructure (potentially)

Active floor l.jpg
Active Floor

  • Instrument floor with load sensors

  • Footsteps and gait detection

Motion detectors l.jpg
Motion Detectors

  • Low-cost

  • Low-resolution

Computer vision l.jpg
Computer Vision

  • Leverage existing infrastructure

  • Requires significant communication and computational resources

  • CCTV

Other systems l.jpg
Other systems?

  • Inertial sensing

  • HVACs

  • Ambient RF

  • etc.

Considerations l.jpg

  • Location type

  • Resolution/Accuracy

  • Infrastructure requirements

  • Data storage (local or central)

  • System type (active, passive)

  • Signaling system