Shwetak N Patel University of Washington http shwetak

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/SP 2014/te. MPCms

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 3 Device is a proxy of a person’s location Used to help derive activity information

Location Tracking 4

Representing Location Information Absolute Relative Geographic coordinates (Lat: 33. 98333, Long: -86. 22444) 1 block north of the main building Symbolic 5 High-level description Home, bedroom, work

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 Wi. Fi Beacons VHF Omni Ranging Ultrasound Ad hoc signal strength Floor pressure Laser range-finding Stereo camera Array microphone Ultrasonic time of flight 9 Infrared proximity E-911 Physical contact

Some outdoor applications E-911 Bus view Car Navigation Child tracking 10

Some indoor applications Elder care 11

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

Approaches for determining location 13 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. 14

Lateration Measure distance between device and reference points 3 reference points needed for 2 D and 4 for 3 D 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 Signal strength 18 Speed of light or sound 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 19

Fingerprinting SSID (Name) 20 BSSID (MAC address) Signal Strength (RSSI) linksys 00: 0 F: 66: 2 A: 61: 00 18 starbucks 00: 0 F: C 8: 00: 15: 13 15 newark wifi 00: 06: 25: 98: 7 A: 0 C 23

Fingerprinting Easier than modeling Requires a dense site survey Usually better for symbolic localization Spatial differentiability Temporal stability 21

Reporting Error 22 Precision vs. Accuracy

Reporting Error Cumulative distribution function (CDF) Accuracy value and/or confusion matrix 23 Absolute location tracking systems Symbolic systems

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 25 IR, RF, Ultrasonic, Vision, Audio, etc

GPS Use 24 satellites TDOA Hyperbolic lateration Civilian GPS L 1 (1575 MHZ) 10 26 meter acc.

Active Badge IR-based Proximity 27

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

Cricket Similar to Active Bat Decentralized compared to Active Bat 29

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

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

RADAR Wi. Fi-based localization Reduce need for new infrastructure Fingerprinting 32

Place Lab http: //research. microsoft. com/apps/pubs/default. aspx? id=64611 “Beacons in the wild” Wi. Fi, Bluetooth, GSM, etc Community authored databases API for a variety of platforms Right. SPOT (MSR) – FM towers http: //msr-waypoint. com/enus/um/people/jckrumm/Publications%202003/right. SPOT%20 publish. pdf 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 -20 m (worse where there are fewer transmitters) 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), Wi. Fi (RADAR, Ekahau, Place Lab), FM (MSR) 35

Limitations Beacon-based solutions Requires the deployment of many devices (typically at least one per room) Maintenance Using existing infrastructure Wi. Fi and GSM Not always dense near some residential areas Little control over infrastructure (especially GSM) 36

n 37 Beacon-based localization

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

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

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

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

Signal Map 42 1 st Floor 2 nd Floor

Example 43

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

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

Motion Detectors Low-cost Low-resolution 46

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

Other systems? Inertial sensing HVACs Ambient RF etc. 48

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

Questions? ? ?

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