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Location Systems for Ubiquitous Computing

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... can locate a person on a train Absolute versus Relative positioning Absolute location systems GPS uses a universal reference grid Two GPS receivers at the ... – PowerPoint PPT presentation

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Title: Location Systems for Ubiquitous Computing


1
Location Systems for Ubiquitous Computing
  • Jeffrey Hightower and Gaetano Borriello

2
Intro
  • Ubiquitous computing
  • a person wanting to know where he was when he did
    a particular task
  • Help rescue teams
  • Customize environment based on location of user
  • devices have already been developed
  • what they sense and how they go about achieving
    it
  • physical attribute used
  • size
  • power usage
  • type of results obtained

3
Physical Position and Symbolic Location
  • Physical
  • GPS - 473917 N by 1221823 W
  • Symbolic
  • Abstract , relative to the position of a known
    object
  • Provide coarse grained location information
  • Derived from Physical-positioning systems
  • Linking real-time train positions to the
    reservation and ticketing database can locate a
    person on a train

4
Absolute versus Relative positioning
  • Absolute location systems GPS uses a universal
    reference grid
  • Two GPS receivers at the same position will show
    the same reading
  • In Relative Systems, each receiver has its own
    frame of reference
  • Devices that use a particular transmitter form a
    grid relative to that transmitter
  • Absolute position can be transformed to a
    relative one relative to another reference
    point

5
Localized Location Computation
  • Object we are interested in computes its own
    location
  • Ensures privacy
  • Does not require the object to transmit
    information for external systems to locate it
  • Burden on the object increases so it is better
    left to the external system

6
Accuracy and Precision
  • Depend on the distribution of error and the
    density of elements
  • Overlapping levels of positioning systems to
    obtain fine grained location information
  • Coping dynamically with failures
  • Suitability for application at hand

7
Scale
  • Coverage of system, the number of objects the
    system can locate per unit area per unit time
  • Communication bandwidth is important
  • Increasing infrastructure

8
Recognition
  • Recognition of located objects to carry out some
    action, like controlling the located device over
    the internet
  • Assigning unique IDs to the located objects
  • Combine contextual information

9
Limitations
  • GPS does not work indoors
  • Interference
  • Characteristics of underlying technologies

10
  • Active Badge
  • Active Bat
  • Cricket
  • RADAR
  • Motionstar Magnetic Tracker
  • Easy Living
  • Smart Floor
  • Enhanced 911

11
Active Badge
  • Uses diffuse infrared technology - flooding an
    area with infra-red light
  • Each badge emits signal with unique id every 10
    seconds that is received by a network of sensors
  • Location is symbolic restricted area like a
    room
  • Range of several meters
  • Has difficulty in presence of sunlight

12
Active Bat
  • Infers location based on time of flight of
    ultrasound pulse
  • Each bat emits an ultrasound pulse with unique id
    to a grid of receivers
  • At the same instant a controller resets the
    receiver
  • Orientation is calculated by analysis
  • Distance is computed from the time interval
    between the reset and receiving the pulse
  • Accurate to within 3cm
  • Paging
  • Requires large sensor infrastructure

13
Cricket
  • fixed ultrasound emitters and mobile receivers
  • time gap to receive the signal is also set in the
    pulse to prevent reflected beams
  • computation takes place at receiver
  • decentralized architecture
  • few centimeters of accuracy
  • computational and power burden

14
RADAR
  • Based purely in software, building on standard RF
    wireless LAN technology
  • Uses signal strength and signal to noise ratio
    from wireless devices
  • Employs multiple base stations with overlapping
    coverage
  • Requires wireless LAN support on objects being
    tracked
  • Generalization to multifloored buildings is a
    problem

15
Motionstar Magnetic Tracker
  • Uses electromagnetic sensing
  • Axial DC magnetic-field pulses are generated
  • Position and orientation are found from by
    measuring the response on the three axes
  • Less than 1mm spatial resolution and 0.1
    orientation
  • Must be within 1-3 meters of transmitter
  • Motion capture for animation

16
Easy Living
  • System to keep track of a room's occupants and
    devices
  • Uses real-time 3D cameras to provide vision
    positioning
  • measures location to roughly 10 cm on the ground
    plane, and it maintains the identity of people
    based on color histograms
  • Difficult to maintain accuracy
  • Aimed for a home environment

17
Smart Floor
  • System for identifying people based on their
    footstep force profiles
  • Does not need device or tag
  • 93 overall user recognition
  • High cost factor

18
Enhanced 911
  • Locates any phone that makes a 911 call
  • reported in most instances with an accuracy of
    100 meters or less
  • Can be enhanced for use by cell phone users
  • Identifying areas of traffic congestion

19
Future Work
  • Integrating multiple systems
  • Overlapping levels off sensing
  • Increases accuracy
  • Ad Hoc Location sensing
  • Cluster of ad hoc objects
  • Relative or absolute
  • Correlation of multiple measurements
  • High scalability

20
Choosing a System
  • Accuracy based comparison
  • Representing error distributions
  • Evaluation
  • Density of elements
  • Prototyping using a simulator
  • Quake iii
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