Context Aware Computing

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Context Aware Computing
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First Paper

• I used mostly A Survey of Context-Aware Mobile
  Computing Research, Chen and Kotz, Dartmouth
  (Tech Report) instead of Schilits paper (which
  is the original paper coining the term)
• Context-aware computing
• Mobile computing application that can discover
  and take advantage of contextual information
• A first step towards ubiquitous computing?
• What is contextual information?
• Example user profile, location, time,
  temperature, nearby people or facilities,
• Instead of adapting systems and applications to
  mobility so that mobility is hidden, explore and
  support new mobile aware applications

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(No Transcript)
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Part I Definitions/Taxonomy
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Defining Context

• Dictionary definition the interrelated
  conditions in which something exists or occurs
• One definition Schilit
• Computing context connectivity, communication
  cost, bandwidth, nearby resources (printers,
  displays, PCs)
• User context user profile, location, nearby
  people, social situation, activity, mood
• Physical context temperature, lighting, noise,
  traffic conditions
• Authors add Time context (time of day, week,
  month, year)
• Context history can also be useful

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Context (contd)

• Is all this information necessary?
• Context is the set of environmental states and
  settings that either determines an applications
  behavior or in which an application event occurs
  and is interesting to the user
• Active context influences the behavior of the
  application
• Location in a call forwarding application
• Passive context context that is relevant but not
  critical
• Active map application display location name and
  other people in the room
• Is all this information measurable?
• Temperature? Location? People around? Social
  situation? Mood?

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Context-Aware computing

• How to take advantage of this context
  information?
• Schilits classification of CA applications
• Proximate selection user interface where nearby
  objects are emphasized/made easier to choose
• Automatic contextual reconfiguration a process
  of adding/removing components or changing
  relationships between components based on context
  change
• Contextual information and commands produce
  different results according to the context in
  which they are issued
• Context-triggered actions rules to specify how
  the system should adapt
• Are these fundamental/inclusive?

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Alternative Taxonomy Pascoe,Dey

• Pascoe Taxonomy of context-aware features
• Contextual sensing how to determine the context
• Contextual resource discovery
• Contextual augmentation how to associate data
  with the context
• Dey maps to services for CA apps
• Presentation of information/services to users
• Execution of services
• Tagging of context to information for later
  retrieval

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Authors classification

• Follows from the definition of context
• Active Context Awareness an application
  automatically adapts to discovered context by
  changing the applications behavior
• Passive context awareness an application
  presents the new or updated context to an
  interested user or makes the context persistent
  for the user to retrieve later

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Part 2 Survey of Context-aware Applications
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App. Survey

• 10 applications surveyed, chronologically
  ordered
• We will look at a few
• Try to notice common threads
• Our second paper is a detailed look at one of
  these applications

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PARCTab System

• Characteristic
• From Xerox Palo Alto Research Center
• 12 applications
• Applications
• Active Map
• Location information
• (Room number)
• The others
• Some helps the user find the most convenient
  local resources
• e.g. nearest printer
• An application makes ParcTab as a remote control

Figure ParcTab Terminal
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Active Badge System

• Characteristic
• From Olivetti Research Lab in 90s
• One of the first context-aware systems
• Office personnel wear badges (IR signal)
• Applications
• Call Forwarding

Figure Locations of the office personnel with
badges
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Call Forwarding

• Location of employees is shown to receptionist
• Receptionist forwards calls to the nearest phone
• Eventually, receptionist was removed from the
  loop calls forwarded automatically
• Is this a good idea?
• What if you were in an important meeting? (or
  taking a nap!)
• What if a private call is forwarded to a non
  private room?
• Context-aware communication
• What is the context?
• What about an active map application?

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Mobisaic Web Browser

• Extend browsers to refer to dynamic contextual
  information
• Dynamic URLs with contextual/environment
  variables
• Variables get bound to current context when the
  URL is referenced
• Also support active documents
• As the context changes, the document is
  automatically updated
• What types of context can be useful here?
• Active or passive?

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Shopping Assistant

• Scenario you are at home depot trying to figure
  out what you need to finish your basement
• Shopping assistant can
• Tell you what parts you need
• Where to find them relative to your location in
  the store
• What is on sale
• Do comparative pricing
• Use your previous profile information to
  customize shopping and delivery
• What context? Active/passive?

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CyberGuide

• Characteristic
• From Georgia Tech
• Provide information services to a tourist
• Direction
• Background information
• Travel diary (automatically recorded)
• Indoor and Outdoor Version
• Indoor
• Using IR (infrared)
• Outdoor
• Using GPS

Figure Outdoor Cyberguide Screenshot, etc.
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Augmented Reality

• Users view of the real world is augmented with
  additional information
• Scenario 1 you wear sun-glasses with a display
  and headphones and walk in downtown Rome
• As you move around, the glasses can tell you your
  location
• As you look at the coliseum you get information
  about it
• Scenario special ops squad infiltrating an enemy
  complex wearing the same gizmos
• In addition to information as above, the glasses
  change to night vision if lighting is not
  sufficient
• Context?

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GUIDE

• Developed in Lancaster University
• For Lancaster City visitors
• Using WaveLAN as communication infrastructure
• A tourist comes to a region(cell), then he
  receives information of the region.
• Information provided using
• Fujitsu TeamPad 7600 portable PC
• Java based http browser

Screenshot of GUIDE
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Adaptive GSM phone/PDA

• PDA notepad application changes its
  characteristics depending on user activity
• Large font when walking, small font when
  stationary
• Change the intensity level depending on the
  lighting conditions
• Phone decide ring volume or vibration depending
  on situation
• In hand, in a suitcase, on a table, in a
  classroom/conference?
• What is the context?

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Conference Assistant

• Assistant checks out conference schedule and
  users interest to highlight which presentations
  should be attended
• Automatically present speaker names, title of
  paper/other relevant info
• May record slides, audio, questions, take notes
  and tag them with the appropriate place in the
  talk for later retrieval

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Location Aware Information Delivery

• Generate reminders to users as they enter
  locations
• Voice synthesis used to generate audio reminders
• Sorry, dear, I forgot is going to become
  obsolete?
• Several projects (MIT, Stanford, GaTech)
• CyberMinder (GaTech) uses a complex context
  including nearby people, weather conditions
• But what is the basic context needed here?

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Observations

• Human-Computer interaction can be improved with
  context info
• Intelligent applications? AI?
• Focus on simple context(s) e.g., location,
  identity, time
• Why arent other contexts used more heavily?
• Not that useful?
• Difficult to sense/model?
• Need more imagination?
• A natural consequence of these being mobile
  applications?
• No killer app
• little gizmos of limited use
• Still to come?

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StartleCam

• From MIT Media Lab
• Composed with
• Wearable video camera
• Computer
• sensing system
• Save Image when the
• wearer is interested
• By sensing skin conductivity signal

Figure StartleCam System
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Sensing Context
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How to sense the context

• Sensing Location Use Global Positioning System
  (GPS)
• Some info http//www.cmtinc.com/gpsbook/index.htm
  
• GPS determines the distance by measuring the time
  it takes a signal to propagate from Satellite to
  receiver
• Need to have very good synchronization of clocks
• Receive signal from three satellites to determine
  location
• Need a fourth satellite to estimate elevation
• Satellite GPS accuracy is getting reasonable
  (10-20 meters)
• Sub-meter accuracy possible with differential GPS
• But what to do indoors?

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Indoors

• GPS doesnt work because the satellite signal is
  weak or reflected (lowers accuracy)
• Need to build our own location tracking system
• difficult problem
• Use ideas similar to GPS compute distances from
  known locations that send beacons

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Location Tracking

• We will look at the Bat system from ATT labs (as
  part of our second paper)
• Cricket (MIT, Mobicom 2001)
• RF and ultrasonic signals sent from each
  basestation
• Mobile estimates distance by time interval
  between the two signal arrivals
• Accuracy within a few feet
• RADAR (Microsoft) and other efforts
• Measure signal strength (or SNR) to estimate
  distance
• A set of static receivers track positions of
  transmitters
• They are queried for location

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Guide System Location Tracking

• Cellular system with base stations at areas of
  interest
• Non-overlapping cells
• Coarse Granularity Location
• You only know what area you are from by knowing
  the basestation that you are in range of
• Cells not overlapping can lose track of location
  completely

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Sensing other low level contexts

• Time?
• Physical sensors possible
• Light, acceleration, tilt, sound, temperature,
  pressure, proximity of humans
• Nearby objects?
• If system keeps track of location of objects,
  query to a database
• Bandwidth? Odyssey
• Orientation?
• Orientation sensor based on two mercury switches
  (Newton MessagePad)
• Directional antennas/directional transmitters?

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High Level contexts

• This is by far the more difficult problem
• Not just an engineering challenge
• Psychology, sociology, ??
• How does a node know whether this is a party or a
  wake?
• Check your calendar or detect the cake/coffin?

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Sensing Context changes

• Publish subscribe model?
• Monitor polls the current context
• Notifies subscribers to the context
• Centralized or on a per-node?
• Polling rate is a function of rate of change of
  context

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Modeling Context Information
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Location Model

• How do we answer questions such as
• Given an object what is its location
• Given a location, return the set of objects there
• Determining paths between locations
• How does a vehicle navigation system do it?
• Geographical Information Systems/Spatial
  Databases
• Already pretty mature (part of Oracle, mysql,
  etc..)
• Model geometry and topology
• Typically locations are organized hierarchically
• Sonal Dedhias project

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Security and Privacy Issues

• I personally hate the idea that someone can know
  my location all the time
• I still refuse to get a cell phone, but it looks
  like I will finally cave in!
• Par for the course, many of these systems ignore
  privacy and security issues

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Second Paper

• The Anatomy of a Context-Aware Application Andy
  Harter, Andy Hopper, Pete Steggles, Andy Ward and
  Paul Webster. ATT Labs, Cambridge, UK (cont)

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Overview

• Paper describes the system components necessary
  to support a context-aware application
• Location system
• Data model
• Distributed object model
• Resource Monitors
• Spatial monitors
• Working system, real details
• So what is the application? Teleporting/follow-me
  
• Application follows you as you move around a
  building
• Hmm!! Virtual dog?
• Definitely some gaming applications
• But what else? Virtual nanny?
• Framework not specific to this application

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Location System

• Would like
• Fine grained (accurate in space)
• High update rate (accurate in time)
• Inexpensive
• Works indoors
• Argue for ultrasonic
• Optical expensive detectors line of sight
  limitations
• GPS dies indoors
• RF multipath

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Bat Unit

• Radio transceiver, ultrasonic transducer and
  control logic
• Each bat has a GUID
• Base station transmits a periodic message with
  the GUID corresponding bat responds with
  ultrasound
• Use speed of sound in air (estimated from ambient
  temperature) to estimate location
• Ultrasonic receivers detect the delay and map it
  to distance
• Use multiple receivers to get 3D location using
  multilateration
• Reflections of ultrasonic waves statistical
  outlier elimination (can same techniques be
  applied to RF multipath?)

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Bat (contd)
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Bat Unit (cont.)

• It takes 20 ms between bat readings 50
  timeslots per base station per second
• Allow echos to die
• Location can be used to measure orientation
• Attach many bats to the same object. Use the
  measurements to infer the orientation
• If too cumbersome, can check shadow of a single
  bat
• Base station can provide Location
  Quality-of-service to allocate time slots to bats
  based on the expected update frequency
• Bats carried by people few times a second
• Bats attached to workstation once every few
  minutes

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Bat Unit (cont.)

• Bats perform handover when moving from one base
  station to another (similar to the cellular
  networks)
• Hand off decisions can also be made based on the
  Bat location
• Battery consumption is low, power consumed
  depends on the update frequency and power state
• Several updates a second several month lifetime
• 95 of samples within 9cms of actual location
• 95 of samples within 25 degrees with multiple
  bats within 70 degrees for a single bat
  (orientation)
• Bat is good enough to be used as a 3D mouse it
  has buttons and can communicate with basestation

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How well does it work?
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Modeling the environment

• Detailed model describing entities in the real
  world and their possible interactions
• Environment consists of real objects should use
  OO modeling (agree?)
• Modeling language based on entity relation
  diagrams and multiple inheritance
• Modeled people, computers, keyboards, monitors,
  networks, telephones and furniture
• Use CORBA and databases to implement persistent
  distributed objects

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3 Tier Architecture
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Populating and Updating the Model

• Some elements are static (e.g., furniture)
• but some are dynamic (e.g., is a keyboard in
  use)
• need to be updated automatically
• Centralized data repository (to optimize
  information access)
• Three classes of resource monitors
• Machine activity e.g. keyboard activity
• Machine resource e.g. CPU usage, memory usage
• Network point-to-point bandwidth and latency

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Client level event filters

• Update Frequency
• The frequency at which items are monitored is
  based on how quickly the item tends to change
• Relevancy
• If a value has not changed significantly, it is
  not sent. This value depends on the data being
  monitored
• Caching
• Caching improves performance at the cost of
  consistency

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Location Update

• Each Bat location is tracked
• Translated into object location in a type
  specific way (e.g., person different than
  workstation)

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API

• Absolute and relative spatial facts
• Person is at (x,y,z) facing in direction ? .vs.
  Person is standing in front of the monitor
• Geometric containment is used for relative
  spatial facts

monitor
person
Contained(person, screenspace)
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Reasoning about Space
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Scalability

• With many devices, containment is complex
• They use containment tree indexing system (a
  quad-tree based approach)

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Implementation

• BAT teleportation system
• With their earlier active badge based
  teleportation system, they only knew that a user
  was in the room and so they had to cycle between
  multiple displays in a room
• If a particular display was being use, they would
  still cycle that display because they did not
  monitor machines
• If a machine is dead, their system would still
  wait because they did not monitor machines
• With the BAT system, they have more accurate
  location information
• Event driven programming style

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Zones and Buttons
Action
monitor
Maintain

• Action zone triggers teleportation
• Within maintain zone, teleported desktops are
  maintained