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/AUT2016/teMPCms

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

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

Location Tracking

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! Accurate Low-cost Easy-to-deploy Ubiquitous Application needs determine technology

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

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

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

Some outdoor applications Bus view Car Navigation Child tracking

Some indoor applications Elder care

Outline Defining location Methods for determining location Systems 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

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

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

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

Angulation Angle of the signals Directional antennas are usually needed

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

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

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

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

Reporting Error Precision vs. Accuracy

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

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

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

Active Badge IR-based Proximity

Active Bat Ultrasonic Time of flight of ultrasonic pings 3cm resolution

Cricket Similar to Active Bat Decentralized compared to Active Bat

Cricket vs Active Bat Privacy preserving Scaling Client costs Active Bat Cricket

Ubisense Ultra-wideband (UWB) 6-8 GHz Time Difference Of Arrival (TDOA) and Angle Of Arrival (AOA) 15-30 cm

RADAR WiFi-based localization Reduce need for new infrastructure Fingerprinting http://research.microsoft.com/en-us/projects/radar/

Place Lab “Beacons in the wild” Community authored databases 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 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.

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. http://gigaom.com/2010/03/01/rosum-tries-to-tune-into-location-via-tv-signals/

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)

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

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)

Beacon-based localization

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

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

PowerLine Positioning https://ubicomplab.cs.washington.edu/ Indoor localization using standard household power lines

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

Signal Map 1st Floor 2nd Floor

Example

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 Instrument floor with load sensors Footsteps and gait detection

Motion Detectors Low-cost Low-resolution

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

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

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

Questions???

References Special thanks to Alex Varshavsky and Gaetano Borriello for their contribution to this content http://abstract.cs.washington.edu/~shwetak/?Research

Assignment #3 Write Short Notes on any 5 of the ubiquitous computing projects at https://ubicomplab.cs.washington. edu/projects