Location in Ubiquitous Computing
13.04.2023
Fatih ÖzlüBilgehan Kürşad Öz
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
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
-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
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
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/
Characteristics
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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
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
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
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
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
Global Positioning System (cont’d)
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http://www.iranmap.com/2010/04/10/gps-signal-and-errors
Active Badge
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Properties•Indoor, Worn badges• Resolution• Active• central database• networked sensors deployed throughout a building
density and placement of the sensors
Active Badge (cont’d)
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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
Active Bat
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The bat in 2012
vs. 1997
The Dark Knight Rises
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.
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
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)
Cricket (cont’d)
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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
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).
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
UbiSense (cont’d)
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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
Radar
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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
Radar (cont’d)
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Metrics• Scalability – dependant of #tags• Resolution – 90% at 6m• Active vs. Passive – active• Centralization – decentralized• Infrastructure – reuse of existing infrastructure
PlaceLab
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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
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
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
PowerLine Positioning
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Prototype PowerLine Positioning tag
Signal generator plug-in modules
Every 1000m
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
PowerLine Positioning (cont’d)
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Metrics• Scalability – dependant of #tags• Resolution – 90% at 1m• Active vs. Passive – needs active tagging• Centralization – local or central• Infrastructure – lower deployment costs
Active Floor
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No tags! Load sensors
Footstep signature
Also by ground reaction force
Tiles
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
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
Airbus (cont’d)
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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
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
Tracking with Cameras (cont’d)
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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
Comparison of Location Systems
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Summary
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• 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!
Thanks For Listening
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Referenced from Article
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Location in UbiquitousComputing
Alexander Varshavsky and Shwetak Patel