Context Sensing

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Context Sensing

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Outline

• Location sensing
• RFID

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Location Sensing

• Location Systems for Ubiquitous Computing,
  Jeffrey Hightower, Gaetano Borriello, University
  of Washington, IEEE Computer Magazine, August
  2001
• Systems and technologies that automatically
  locate people, equipment, and other tangibles.
• Develop a taxonomy to help developers of
  location-aware applications better evaluate their
  options when choosing a location-sensing system

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Outline Location Sensing

• Introduction
• Location Systems
• Techniques
• Properties
• Survey of Location Systems
• Research Directions
• Summary

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Techniques

• Triangulation
• Use the geometric properties of triangles to
  compute object locations.
• Proximity
• Measure nearness to a known set of points.
• The objects presence is sensed using a physical
  phenomenon with limited range.
• Scene Analysis
• Use features of a scene observed from a
  particular vantage point to draw conclusions
  about the location of the observer or of objects
  in the scene.

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Techniques Triangulation

• Lateration Compute the position of an object by
  measuring its distance from multiple reference
  positions
• Direct
• Physical action or movement.
• Time-of-Flight
• Measure the time it takes to travel between the
  object and point P at a known velocity.
• Attenuation
• Given a function correlating attenuation and
  distance for a type of emission and the original
  strength of the emission

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Techniques Triangulation
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Techniques Angulation

• Use primarily angle or bearing measurements
• 2D angulation requires two angle measurements and
  one length measurement such as the distance
  between the reference points.

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Techniques Scene Analysis

• Static
• Observed features are looked up in a predefined
  dataset that maps them to object locations.
• Differential
• Tracks the difference between successive scenes
  to estimate location.

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Techniques Scene Analysis

• Advantages
• The location of objects can be inferred using
  passive observation and features that do not
  correspond to geometric angles or distances.
• Disadvantages
• The observer needs to have access to the features
  of the environment against which it will compare
  its observed scenes.

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Techniques Proximity

• Detecting physical contact
• Detect physical contact with an object
• Include pressure sensors, touch sensors,
• Monitoring wireless cellular access points
• Monitoring when a mobile object device is in
  range of one or more access points in a wireless
  cellular network
• Observing automatic ID systems
• If the device scanning the label, interrogating
  the tag, or monitoring the transaction has a know
  location, the location of the mobile object can
  be inferred.

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Outline Location Sensing

• Introduction
• Location Systems
• Techniques
• Properties
• Survey of Location Systems
• Research Directions
• Summary

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Properties

• Physical position and Symbolic position
• Absolute versus Relative
• Localized location computation
• Accuracy and Precision
• Scale
• Recognition
• Cost
• Limitations

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Properties Physical and Symbolic Positions

• Physical
• A building situated at 473917N by 1221823W,
  at a 20.5-meter elevation
• E.g., GPS
• Symbolic
• Encompass abstract ideas of where something is
• E.g., in the kitchen, near to a mailbox, a train
  approach Denver,

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Properties Physical and Symbolic Positions

• Physical position
• Can be augmented to provide symbolic location
  with additional information, infrastructure, or
  both, e.g., linking train positions to
  reservation and ticketing database can help
  locate a passenger on a train
• Can determine a range of symbolic information,
  e.g., use a GPS to find the closest printer, or
  link GPS with calendar to provide current
  activity of a person
• Purely symbolic location systems typically
  provide coarse-grained physical positions
• Increase accuracy may need multiple readings or
  sensors

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Properties Absolute versus Relative

• Absolute
• Use a shared reference grid of all located
  objects
• All GPS receivers use latitude, longitude, and
  altitude Two GPS receivers placed at the same
  position will report same position readings, and
  refers to the same place regardless of GPS
  receiver
• Relative
• Each object can have its own frame of reference
• For example, a mountain rescue team searching for
  avalanche victims can use handheld computers to
  locate victims avalanche transceivers. Each
  rescuers device reports the victims position
  relative to itself.

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Properties Absolute versus Relative

• An absolute location can be transformed into a
  relative location
• Relative to a second reference point, but may not
  always available
• In reverse, we can use triangulation to determine
  an absolute position from multiple relative
  reference points.

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Properties Localized Location Computation

• Ensures privacy by mandating that no other entity
  may know where the located object is unless it
  specifically publicizes that information
• Some systems require the located object to
  periodically broadcast, respond with, or
  otherwise emit telemetry to allow the external
  infrastructure to located it
• Infrastructure can find objects in its purview
  without directly involving the objects in the
  computation
• Reduce computational and power demands on the
  objects being located gt lower costs and smaller
  form factors

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Properties Accuracy and Precision

• Some GPS receiver can locate position to within
  10 m for 95 of measurements
• The distances denote the accuracy, or grain size,
  of the position information GPS can provide
• The percentages denote precision, or how often we
  can expect to get that accuracy
• Sensor Fusion seeks to improve accuracy and
  precision by integrating many location or
  position systems to form hierarchical and
  overlapping levels of resolution, e.g., Robot

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Properties Scale

• Scale locating objects worldwide, within a
  metropolitan area, throughout a campus, in a
  particular building, or within a single room
• Assessing coverage area per unit of
  infrastructure and objects the system can
  locate per unit of infrastructure per time
  interval
• Systems can often expand to a larger scale by
  increasing the infrastructure, e.g., a tag system
  that locates objects in a single building can
  operate on a campus by outfitting all campus
  buildings and outdoor areas with the necessary
  sensor infrastructure

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Properties Scale

• Hindrances to scalability in a location system
  include not only the infrastructure cost but also
  middleware complexity

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Properties Recognition

• For applications that need to recognize or
  classify located objects to take a specific
  action based on their location, an automatic
  identification mechanism is needed.
• For example, a modern airport baggage handling
  system needs to automatically route outbound and
  inbound luggage to the correct flight or claim
  carousel
• Systems with recognition capability may recognize
  only some feature types
• For example, cameras and vision systems can
  easily distinguish the color or shape of an
  object but cannot automatically recognize
  individual people

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Properties Recognition

• A general technique for providing recognition
  capability assigns names or globally unique IDs
  (GUID) to objects the system locates
• It can also combine the GUID with other
  contextual information so it can interpret the
  same object differently under varying
  circumstances.
• For example, a person can retrieve the
  descriptions of objects in a museum in a
  specified language.

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Properties Cost

• Time Cost
• Installation processs length and the systems
  administration needs
• Space Cost
• Amount of installed infrastructure and the
  hardwares size and form factor
• Capital Cost
• Price per mobile unit or infrastructure element
  and the salaries of support personnel
• GPS receivers need an antenna of sufficient size
  for adequate satellite reception and may need a
  second antenna to receive the land-based
  differential signal.

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Properties Limitations

• Some system will not function in certain
  environments
• GPS receivers usually cannot detect satellites
  transmissions indoors
• Possible solution uses a system of GPS repeaters
  mounted at the edges of buildings to rebroadcast
  the signals inside
• In general, we assess functional limitations by
  considering the characteristics of the underlying
  technologies that implement the location system.

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Outline Location Sensing

• Introduction
• Location Systems
• Techniques
• Properties
• Survey of Location Systems
• Research Directions
• Summary

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Survey of Location Systems

• Global Positioning System (GPS)
• Active Badge
• Developed at Olivetti Research Lab., now ATT
  Cambridge
• Active Bat
• Developed by ATT
• MotionStar magnetic tracker
• Developed by Ascension
• SpotON
• Developed by Washington

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Global Positioning System (GPS)

• GPS satellites (243)
• Have no knowledge about who uses the signals they
  transmit
• Are precisely synchronized with each other and
  transmit their local time in the signal allowing
  receivers to compute the difference in
  time-of-flight
• Receivers
• Allow receivers to compute their location to
  within 1 to 5 meters
• Receivers can compute 3-D position using 4
  satellites

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Global Positioning System (GPS)
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Active Badge

• A cellular proximity system using diffuse
  infrared
• Usage
• Person wears a small infrared badge
• Badge emits a unique id every 10 sec or on demand
• Central server collects data from fixed infrared
  sensors around the building, aggregates it, and
  provides an API for using the data
• Provide absolute location information
• Location is symbolic, representing, for example,
  the room in which the badge is located

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Active Badge
Four generations of the Active Badge
Network sensor (contains two 87C751
microprocessor
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Active Badge Limitations

• As with any diffuse infrared system, Active
  Badges have difficulty in locations with
  fluorescent lighting or direct sunlight because
  of the spurious infrared emissions that these
  light sources generate
• Diffuse infrared has an effective range of
  several meters, which limits cell sizes to small-
  or medium-sized rooms

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Active Bat

• Uses ultrasound time-of-flight lateration
• Provide more accurate positioning than Active
  Badge
• Usage
• Users and objects carry Active Bat tags
• Each Bat has a GUID for addressing and
  recognition
• In response to a request the controller sends via
  short-range radio, a Bat emits an ultrasonic
  pulse to a grid of ceiling-mounted receivers
• Each ceiling sensor measures time interval from
  reset to ultrasonic pulse arrival and computes
  the distance
• Local controller then forwards the distance
  measurements to a central controller

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Active Bat
Bat (7.5cm3.5cm1.5cm) Power 3.6 V Lifetime
around 15 months Unique 48-bit code Bi-directional
433MHz radio Two buttons, two LEDs, a
speaker, and a voltage monitor
Placed in a square grid, 1.2m apart Connected by
a high-speed serial network The serial network
is terminated by a DSP calculation board
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Active Bat Limitations

• The system can locate Bats to within 9 cm of
  their true position for 95 percent of the
  measurements, and work to improve the accuracy
  even further is in progress
• Require a large fixed-sensor infrastructure
  throughout the ceiling
• Rather sensitive to the precise placement of
  these sensors.
• Disadvantages scalability, ease of deployment,
  and cost

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MotionStar Magnetic Tracker

• Use scene analysis, lateration and
  electronmagnetic sensing
• Tracking systems uses DC magnetic sensors to
  overcome blocking and post processing delays .
• System computes the position and orientation of
  the receiving antennas by measuring the response
  in three orthogonal axes to the transmitted field
  pulse, combined with the constant effect of the
  earths magnetic field

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MotionStar Magnetic Tracker
MotionStar Wireless (Magnetic pulse transmitting
antennas receiving antennas and Controller)
MotionStar Controller
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MotionStar Magnetic Tracker

• Sense precise physical positions relative to the
  magnetic transmitting antenna
• Advantages
• Very high precision and accuracy
• Disadvantages
• Steep implementation costs and the need to tether
  the tracked object to a control unit

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SpotON

• Implement ad hoc lateration with low-cost tags
• Ad-hoc location sensing is a fusion of concepts
  from object location tracking and the theories of
  ad-hoc networking
• SpotON tags use radio signal strength information
  (RSSI) as a distance estimator to perform ad-hoc
  lateration.

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SpotON
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Outline Location Sensing

• Introduction
• Location Systems
• Techniques
• Properties
• Survey of Location Systems
• Research Directions
• Summary

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Sensor Fusion

• The use of multiple technologies or location
  systems simultaneously to form hierarchical and
  overlapping levels of sensing
• Provide aggregate properties unavailable when
  using location systems individually
• For example, integrating several systems with
  different error distributions may increase
  accuracy and precision beyond what is possible
  using an individual system

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Ad hoc Location Sensing

• Locating objects without drawing on the
  infrastructure or central control
• In a purely ad hoc location-sensing system, all
  of the entities become mobile objects with the
  same sensors and capabilities
• To estimate their locations, objects cooperate
  with other nearby objects by sharing sensor data
  to factor out overall measurement error
• Cluster-based approach Objects in the cluster
  are located relative to one another or absolutely
  if some objects in the cluster occupy known
  locations

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Location Sensing System Accuracy

• Comparing the accuracy and precision of different
  location sensing systems
• Need quantitative evaluations
• Should include error distribution, summary of
  accuracy and precision and any relevant
  dependencies, e.g. density of infrastructural
  elements
• Accurately described error distribution can be
  used as partial input for simulating a systemgt
  use of simulation for evaluation

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Outline Location Sensing

• Introduction
• Location Systems
• Techniques
• Properties
• Survey of Location Systems
• Research Directions
• Summary

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Location Sensing Summary

• Location sensing is a mature enough field to
  define a space within a taxonomy that is
  generally populated by existing systems
• Future work should generally focus on
• Lowering cost
• Reducing the amount of infrastructure
• Improving scalability
• Creating systems that are more flexible within
  the taxonomy

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Outline

• Location sensing
• RFID

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Outline RFID

• System Components
• Transponders/Tags
• Reader/Interrogator
• RF Transponder Programmers
• RFID System Categories
• Areas of Application for RFID

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What is RFID?

• Radio Frequency Identification
• Basic components
• An antenna or coil
• A transceiver (with decoder) or reader
• A transponder (RF Tag), electronically programmed
  with unique information
• Data are carried intransponders to
  provideidentification

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System Components
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Transponder
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Active Transponders

• Powered by an internal battery and are typically
  read/write devices
• Principle of operation propagation coupling
• based upon propagating electromagnetic waves
• Tags have
• Microprocessor
• Memory (up to 1MB)
• Metal coil (antenna)
• Separate power source

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Passive Transponders

• Operate without an internal battery source,
  deriving the power to operate from the field
  generated by the reader
• Principle of operations inductive coupling
• based upon close proximity electromagnetic
• Tags have
• Microprocessor
• Small memory (32-128 bits)
• Metal coil (antenna)
• Separate power source

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Comparing Passive and Active Tags

• Active
• greater communication range
• better noise immunity
• higher data transmissions rates
• usually capable of operating over a temperature
  range of -50 C to 70 C
• Greater size
• Greater cost
• Limited operation life (10 years)

• Passive
• lighter, smaller
• less expensive
• unlimited operation life
• small read range
• require a higher-powered reader
• sensitivity and orientation performance may also
  be constrained by the limitation on available
  power

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Data Carrying Options

• Tags may be used to carry
• Identifiersa numeric or alphanumeric string is
  stored for identification purposes or as an
  access key to data stored elsewhere in a computer
  or information management system
• Portable data filesinformation can be
  organized, for communication or as a means of
  initiating actions without recourse to, or in
  combination with, data stored elsewhere

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Data Capacity

• Single bit
• For surveillance, e.g., retail electronic article
  surveillance (EAS)
• May also be used for counting
• Up to 128 bits
• Can hold serial no. or id with parity check
• May be manufacturer or user programmable
• Up to 512 bits
• Mostly user programmable
• Can hold id, package content, process
  instructions
• Around 64 kilobits
• As carriers for portable data files

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Transponder Memory

• ROM
• Security data
• OS instructions in conjunction with the
  processor or processing logic deals with the
  internal "house-keeping" functions such as
  response delay timing, data flow control and
  power supply switching.
• RAM
• Used to facilitate temporary data storage during
  transponder interrogation and response.

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Transponder Memory

• Non-volatile programmable memory
• Electrically erasable programmable read only
  memory (EEPROM) being typical
• Store transponder data and ensure that the data
  is retained when the device is in its quiescent
  or power-saving "sleep" state
• Data buffers are further components of memory
• Used to temporarily hold incoming data following
  demodulation and outgoing data for modulation and
  interface with the transponder antenna

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Data Read Rate
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Communication Range

• The range is determined by
• The power available at the reader/interrogator to
  communicate with the tag(s)
• The power available within the tag to respond
• The antenna design will determine the shape of
  the field or propagation wave delivered.
• The environmental conditions and structures
• noise ratio
• obstructions or absorption mechanisms
• moisture

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Data Programming Options

• read-only
• write once read many (WORM)
• User-programmable (at beginning)
• read/write
• User-programmable
• Allowing the user to change data stored in a tag

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Physical Form

• Animal tracking tags inserted beneath the skin,
  can be as small as a pencil lead in diameter and
  ten millimeters in length
• Tags can be screw-shaped to identify trees or
  wooden items
• Credit-card shaped for use in access applications
• Plastic or printed for placing on packages

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Reader/Interrogator/Transceiver

• Transmitter and receiver
• Larger antenna
• Larger coil (energizing the tag)
• Draws power from external power supply

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Reader

• Command response protocol (hands down polling)
• Once the signal from a transponder has been
  correctly received and decoded, algorithms may be
  applied to decide whether the signal is a repeat
  transmission, and may then instruct the
  transponder to cease transmitting
• Used to circumvent the problem of reading
  multiple tags in a short period of time

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Reader

• Hands up polling
• The interrogator looks for tags with specific
  identities, and interrogates them in turn
• This is contention management, and a variety of
  techniques have been developed to improve the
  process of batch reading
• A further approach may use multiple readers,
  multiplexed into one interrogator, but with
  attendant increases in costs

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RF Transponder Programmers

• Programming is generally carried out off-line,
  e.g., at the beginning of a batch production run
• For some systems re-programming may be carried
  out on-line, particularly if it is being used as
  an interactive portable data file within a
  production environment
• By combining the functions of a
  reader/interrogator and a programmer, data may be
  appended or altered in the transponder as required

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Outline RFID

• System Components
• Transponders/Tags
• Reader/Interrogator
• RF Transponder Programmers
• RFID System Categories
• Areas of Application for RFID

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RFID System Categories

• EAS (Electronic Article Surveillance) systems
• Typically a one bit system to sense the
  presence/absence of an item, usually in retail
  stores
• Portable data capture system
• Portable data terminals with integral RFID reader
• Capture data which is then either transmitted
  directly to a host information management system
  via a radio frequency data communication (RFDC)
  link or held for delivery by line-linkage to the
  host on a batch processing basis

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RFID System Categories

• Networked systems
• Fixed position readers deployed within a given
  site and connected directly to a networked
  information management system
• The transponders are positioned on moving or
  moveable items, or people
• Positioning systems
• Readers are positioned on the vehicles and linked
  to an on-board computer and RFDC link to the host
  information management system

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Outline RFID

• System Components
• Transponders/Tags
• Reader/Interrogator
• RF Transponder Programmers
• RFID System Categories
• Areas of Application for RFID

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Typical Areas of Application

• Transportation and logistics
• Manufacturing and processing
• Security
• Miscellaneous
• Animal tagging
• Waste management
• Time and attendance
• Postal tracking
• Airline baggage reconciliation
• Road toll management

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New Areas of Application

• Electronic article surveillance
• Vehicle anti-theft systems
• Electronic monitoring of offenders at home
• Time and attendance
• To replace conventional "slot card" time keeping
  systems.

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Example Application 1

• Consider a book consisting of a collection of
  printed pages
• When a computational device detects the tag, an
  associated virtual document is displayed
• You can always read the latest electrical version

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Example Application 2

• Augmenting business cards
• A tag is placed on the back of a regular business
  card
• When the card is brought close to the computer,
  the corresponding homepage is displayed

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Example Application 3

• Extending document functionality services
• We can link to the corresponding Amazon.com web
  page to order a copy of the book
• We can additionally link in theauthors
  homepage, reviews of thebook, or other
  correspondencerelated to the book

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Example Application 4

• Augmenting non-document objects wristwatch
• A tag is embedded in a wristwatch
• When the watch is close to thecomputer, the
  calendar applicationfor the particular user is
  shown forthe current day, at the current time

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References

• http//www.aimglobal.org
• http//www.TLCdelivers.com
• www.ems-rfid.com