Transcript PED - Microsoft Research
Location in Pervasive Computing
Shwetak N. Patel
University of Washington
More info: shwetak.com
design: use: build: university of washington
Special thanks to Alex Varshavsky and Gaetano Borriello for their contribution to this content ubi comp
lab university of washington Computer Science & Engineering Electrical Engineering
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 2
Location Well studied topic (3,000+ PhD theses??) Application dependent Research areas Technology Algorithms and data analysis Visualization Evaluation 3
Location Tracking 4
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 5
No one size fits all!
Accurate Low-cost Easy-to-deploy Ubiquitous Application needs determine technology 6
Consider for example… Motion capture Car navigation system Finding a lost object Weather information Printing a document 7
Others aspects of location information
Indoor vs. outdoor Absolute vs. relative Representation of uncertainty Privacy model 8
Lots of technologies!
GPS WiFi Beacons Ultrasound Floor pressure VHF Omni Ranging Ad hoc signal strength Laser range-finding Stereo camera Ultrasonic time of flight Array microphone Infrared proximity E-911 Physical contact
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Some outdoor applications
E-911 Bus view Car Navigation Child tracking
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Some indoor applications
Elder care
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Outline
Defining location Methods for determining location Ex. Triangulation, trilateration, etc.
Systems Challenges and Design Decisions Considerations
Approaches for determining location Localization algorithms Proximity Lateration Hyperbolic Lateration Angulation Fingerprinting Distance estimates Time of Flight Signal Strength Attenuation 13
Proximity Simplest positioning technique Closeness to a reference point Based on loudness, physical contact, etc 14
Lateration Measure distance between device and reference points 3 reference points needed for 2D and 4 for 3D 15
Hyperbolic Lateration Time difference of arrival (TDOA) Signal restricted to a hyperbola 16
Angulation Angle of the signals Directional antennas are usually needed 17
Determining Distance Time of flight Speed of light or sound Signal strength Known drop off characteristics 1/r^2-1/r^6 Problems: Multipath 18
Fingerprinting Mapping solution Address problems with multipath Better than modeling complex RF propagation pattern 19
Fingerprinting
SSID (Name)
linksys starbucks newark wifi
BSSID (MAC address)
00:0F:66:2A:61:00 00:0F:C8:00:15:13 00:06:25:98:7A:0C 18 15 23
Signal Strength (RSSI)
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Fingerprinting Easier than modeling Requires a dense site survey Usually better for symbolic localization Spatial differentiability Temporal stability 21
Reporting Error Precision vs. Accuracy 22
Reporting Error Cumulative distribution function (CDF) Absolute location tracking systems
CDF of Localization error 1 0.9
0.8
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1 1.5
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Error (m) 3 3.5
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Accuracy value and/or confusion matrix Symbolic systems 23
Location Systems Distinguished by their underlying signaling system IR, RF, Ultrasonic, Vision, Audio, etc 24
GPS Use 24 satellites TDOA Hyperbolic lateration Civilian GPS L1 (1575 MHZ) 10 meter acc.
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Active Badge IR-based Proximity 26
Active Bat Ultrasonic Time of flight of ultrasonic pings 3cm resolution 27
Cricket Similar to Active Bat Decentralized compared to Active Bat 28
Cricket vs Active Bat Privacy preserving Scaling Client costs
Active Bat Cricket
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Ubisense Ultra-wideband (UWB) 6-8 GHz Time difference of arrival (TDOA) and Angle of arrival (AOA) 15-30 cm 30
RADAR WiFi-based localization Reduce need for new infrastructure Fingerprinting 31
Place Lab “Beacons in the wild” WiFi, Bluetooth, GSM, etc Community authored databases API for a variety of platforms RightSPOT (MSR) – FM towers 32
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) 33
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) 34
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) 35
Beacon-based localization 36
Wifi localization (ex. Ekahau) 37
GSM localization
Tower IDs and signals change over time!
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PowerLine Positioning
Indoor localization using standard household power lines 39
Signal Detection
A tag detects these signals radiating from the electrical wiring at a given location 40
Signal Map
1 st Floor 2 nd Floor
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Example
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Passive location tracking
No need to carry a tag or device Hard to determine the identity of the person Requires more infrastructure (potentially) 43
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Active Floor
Instrument floor with load sensors Footsteps and gait detection 44
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Motion Detectors
Low-cost Low-resolution 45
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Computer Vision
Leverage existing infrastructure Requires significant communication and computational resources CCTV 46
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Other systems?
Inertial sensing HVACs Ambient RF etc.
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Considerations
Location type Resolution/Accuracy Infrastructure requirements Data storage (local or central) System type (active, passive) Signaling system 48