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Location in Ubiquitous Computing
13.04.2023
Fatih ÖzlüBilgehan Kürşad Öz
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OUTLINE
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1.LOCATION TECHNOLOGIES• Introduction• Location Representation • Infrastructure&Client-Based
Location Systems • Approaches to Determining
Location• Error Sources in Location
Systems
2.LOCATION SYSTEMS• Global Positioning System,
Active Badge, Active Bat, Cricket, UbiSense, RADAR, Place Lab, PowerLine Positioning, ActiveFloor, Airbus, Tracking with Cameras
• Comparisons of Location Systems
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IntroductionDetermining location
• Specific location
• Context
information
• Context aware
applications
ExamplesEntertainment,
Navigation,Asset tracking,
Healthcare monitoring,Emergency responseTrade-offs: accuracy, range and cost
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Location Representation
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FORMS:• Absolute• Relative• Symbolic
• Indoor Location
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Infrastructure&Client-Based Location
SystemsTHREE CLASSES of LS
• client-based
Gps
• network-based
Active Badge
• network-assisted
aGps
• LOCATION PRIVACY
X• Battery Life• Processing
and Store Capability
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Approaches to Determining Location
• Proximity• Trilateration• Time of Flight• Signal Strength Attenuation
• Hyperbolic Lateration• Triangulation• Dead Reckoning
reference points>1GPS satelliteWiFi access
pointCellular Tower
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Proximity
examples
• NFC in cms
• Bluetooth
10ms
• WiFi 100ms
• Cellular phone
kms
• device vs reference
point
• closeness of a device
• more RP -> more
accuracy
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Trilateration
• distance between a
device and a
number of
reference points
• intersections of
reference point
circles
• types:
time of flight of
signal
attenuation of
the strength of
the signal
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Trilateration /Time of FlightKNOWN
• Speed of Sound :344 meters per second in
21° C
• Speed of Light :299,792,458 meters per
second
EASY TO CALCULATE!
X = V.t
NEEDS
• precise clock
synchronization
• instead round trip
delay
EXAMPLES:radio or light signal
for light,
ultrasonic pulse for sound
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-decrease of the
signal’s strength by
factor of 1/r²
-r:distance from
source
Challenges-signal propagation medium-reflaction, diffraction,changing direction
Trilateration /Signal Strength
Attenuation
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Hyperbolic Lateration
CALCULATION
• time difference
between signal
arrival times to
more 3 rp.
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Triangulation
the angle of arrival (AOA) of signals to
reference points
!angle measurement
errors.
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Dead Reckoning
USES
• previously known
location
• elapsed time
• direction
• average speed
DEPENDS ONaccuracy of speed
and direction,use of accelemators
for acceleration, odometers for
distance, gyroscope for direction
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Error Sources
AIM
• produce
accurate
location
estimates
Sources of Errors•Incorrect reference point coordinates•Delay in signal•Clock synchronization•Multipath•Geometry
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LOCATION SYSTEMS
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• Based on the general concepts discussed• Commercial & research systems• Historically important and current systems• Differing characteristics among the solutions
http://www.toasystems.com/
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Characteristics
13.04.2023
Metrics for Evaluation• Scalability• Resolution• Active vs. Passive• Centralization• Infrastructure
http://www.army-technology.com/features/feature121877/feature121877-1.html
http://www.pixavi.com/systems-wireless-telemetry.html
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Characteristics (cont’d)
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Properties
• Scalability• Resolution• Active vs. Passive• Centralization• Infrastructure
Concerns
• Indoor/Outdoor, Pervasiveness• Accuracy, Performance• Initiating, Tag Carrying• Privacy Concerns• Multiple Deployment, Cost
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Global Positioning System
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GPS• Most popular outdoor location tracking system
• Indoor tracking problematic building occlusions
• Started as 24 satellites orbiting the Earth, Now 30
http://www.nist.gov/pml/div688/grp40/gpsarchive.cfm
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Global Positioning System (cont’d)
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• Satellite transmission location and the current time various frequencies• Receiver
distance to satellite calculated• Signal ID code, ephemeris data, almanac
data
At least 4 satellite needed!
Which satellite?
Status, date, time
Orbital data
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Global Positioning System (cont’d)
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• Signals’ travel time the time difference of arrival (TDOA)
• Location hyperbolic lateration in 3-D TDOA values• Fourth satellite is required to correct any synchronization errors
Multipath, Atmospheric delays
Negative effect
Minimizing Errors• Predicting atmospheric delays• Increase the number of channels• Correction codes
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Global Positioning System (cont’d)
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http://www.iranmap.com/2010/04/10/gps-signal-and-errors
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Active Badge
13.04.2023
Properties•Indoor, Worn badges• Resolution• Active• central database• networked sensors deployed throughout a building
density and placement of the sensors
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Active Badge (cont’d)
13.04.2023
Metrics• Scalability – difficult deployment• Resolution – high if well deployed• Active vs. Passive – needs active tagging• Centralization – keeps a centralized db and a lookup table• Infrastructure – low cost IR, room specific sensors
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Active Bat
13.04.2023
The bat in 2012
vs. 1997
The Dark Knight Rises
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Active Bat (cont’d)
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Properties• Ultrasound pulse’s travel time and location trilateration initiating with RF signal
Vlight > Vsound
• Multiple tags must coordinate their pulses so as not to interfere with each other’s time-of-flight calculations.
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Active Bat (cont’d)
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Metrics• Scalability – more tags cause interference, activeness decreases scalability• Resolution – 90% at 3cm• Active vs. Passive – needs active tagging,if passive RF signalling independant of #tags• Centralization – central server, managing use of ultrasound bandwith, lack of privacy• Infrastructure – difficult to deploy
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Cricket
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RF transmitter/receiver,Ultrasonic signal receiver, microcontroller
Properties• No centralized architecture!• Tags compute their own location• Method similar to Active Bat
Tag
Transmitter(beacon)
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Cricket (cont’d)
13.04.2023
Metrics• Scalability – independant of #tags• Resolution – 90% at 3cm• Active vs. Passive – passive• Centralization – decentralized, preservesprivacy by local calculations• Infrastructure – no networking between beacons, difficult to deploy because of line-of-sight operation
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UbiSense
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• Ultrawideband (UWB) signal for localization • Each Ubitagincorporates a conventional RF radio (2.4 GHz) and a UWB radio (6–8 GHz).
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UbiSense (cont’d)
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• Time and Location the time difference of arrival (TDOA)
angle of arrival (AOA) triangulation
At least two UbiSensors
• Advantage of using UWB pulses is that it iseasier to filter multipath signals and can endure some occlusion
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UbiSense (cont’d)
13.04.2023
Metrics• Scalability – dependant of #tags, separate coordination channel in favor• Resolution – 90% at 15cm• Active vs. Passive – active• Centralization – centralized• Infrastructure – physical timing cable, difficult to deploy because of line-of-sight operation
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Radar
13.04.2023
Properties• RF signal strength as indicator of the distance between an AP and a receiver. Makes use of 802.11 WiFi network.• Consumer does not have to purchase any specialized equipment (WiFi-enabled mobile phones, PDAs can be handled as a receiver or tag.)• Problems with multipath led researchers to use a mapping approach for localization• Receiver measures signal strength and compares it with the offline signal map• Subject to environment change
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Radar (cont’d)
13.04.2023
Metrics• Scalability – dependant of #tags• Resolution – 90% at 6m• Active vs. Passive – active• Centralization – decentralized• Infrastructure – reuse of existing infrastructure
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PlaceLab
13.04.2023
Properties• software-based indoor and outdoorlocalization system.
• Makes use of 802.11 WiFi network. GSM towers, Bluetooth• detecting multiple unique IDs from these existing radio beacons and referring to a map of these devices
So far localization similar to RADAR...• location tracking at a larger scale outdoor• Less dense calibration data, no need for an individual to populate a signal map no surveying
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PlaceLab
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War Driving• War driving is the process of driving around with a mobile device equipped with a GPS receiver and an 802.11, GSM, and/or Bluetooth radio to collect traces of wireless base stations.
time-stamped recordings containing GPS coordinates
the associated signal strength of the beacons
Location• Position of the device is a weighted average of positions ofthe overheard beacons
millions of beacon estimatesalready determined
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PlaceLab (cont’d)
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Metrics• Scalability – makes use of already determined estimations, still dependant on existance of tags • Resolution – 90% at 20m• Active vs. Passive – active• Centralization – no central provider, clients can determine their location privately• Infrastructure – reuse of existing infrastructure
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PowerLine Positioning
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Prototype PowerLine Positioning tag
Signal generator plug-in modules
Every 1000m
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PowerLine Positioning (cont’d)
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Properties• drawbacks to relying on public infrastructure• indoor localization to work in nearly every building
use the power line as the signaling infrastructure!
• modules continually emit their respective signalsover the power line, tags sense these signals in a building, relay them wirelessly to a receiver • site surveying needed
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PowerLine Positioning (cont’d)
13.04.2023
Metrics• Scalability – dependant of #tags• Resolution – 90% at 1m• Active vs. Passive – needs active tagging• Centralization – local or central• Infrastructure – lower deployment costs
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Active Floor
13.04.2023
No tags! Load sensors
Footstep signature
Also by ground reaction force
Tiles
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Active Floor (cont’d)
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Metrics• Scalability – independant of clients, assuming only one individual on a single tile• Resolution – 91% at 1m• Active vs. Passive – passive• Centralization – central• Infrastructure – custom tiles makes deployment difficult
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Airbus
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• detecting gross human movement and room transitionsby sensing differential air pressure
central heating, ventilation, and air conditioning (HVAC)
• less obtrusive than installing motion detectors
• presence of a person• mass rather than individual
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Airbus (cont’d)
13.04.2023
Metrics• Scalability – scalable in the installed environment• Resolution – 88% at room level• Active vs. Passive – passive• Centralization – central, HVAC is the single monitoring point• Infrastructure – less additional infrastructure for deployment
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Tracking with Cameras
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Properties• cameras and computer vision techniques• no specialized tag and possible to leverage existing cameras• stereo camera images for locating the position, color imagesfor inferring identities• face recognitionOn The Other Hand;• occlusions• dependant on the field of view of cameras, difficult coordination, small close space tracking not possible• privacy concerns
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Tracking with Cameras (cont’d)
13.04.2023
Metrics• Scalability – scalable, independant of #people• Resolution – 50% to 80% at 1m• Active vs. Passive – passive• Centralization – central• Infrastructure – reuse of existing infrastructure is possible
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Comparison of Location Systems
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Summary
13.04.2023
• basic concepts of location technologies• current and historical location systems• client-based vs. network-based positioning• major sources of error• challenges and opportunities
No single location technology today that is ubiquitous, accurate, low-cost and easy to deploy. Road to integration!
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Thanks For Listening
13.04.2023
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Referenced from Article
13.04.2023
Location in UbiquitousComputing
Alexander Varshavsky and Shwetak Patel