Location in Ubiquitous Computing

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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

13.04.2023

Location in UbiquitousComputing

Alexander Varshavsky and Shwetak Patel