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Why context-awareness (CA)?

  • People react on same inputs differently depending on the context
  • To make use of Apps & services easier
    • Computers do the work for user
    • E.g. Aid user find relevant information for a given context
  • Added inteligence for automating processes


  • Many definitions by different researchers in the field
    • Dictionary –> context: surrounding conditions
  • Context adds semantic meaning to raw data
    • E.g. coordinate points to locations having contextual meaning
    • x=123,y=456 —> home
  • Context can be defined for different objects
    • E.g. Person, Place, Object, Activity

Different kinds of context

  • Location
    • Europe, Finland, Lappeenranta, …
  • Time
    • 2010, Autumn, October, Thursday, …
  • Activity
    • Meeting, sleeping, watching tv, …
  • Identity
    • Interests, preferences, associations, relations, …
  • Environmental
    • Light level, noise level, polution level, …
  • Behaviour
    • Heart rate, pulse, role, …

Context sources

  • Fetch context from user
    • Explicitly request customer
      • Customer should not be over-burdened
    • Implicitly
      • Via communication with user's device, calendar (meeting, work, vacation, …)
  • Through context gathering & context reasoning
  • Gathering from different sources
    • Integrated sensors
      • Device speed, temprature, location, …
    • Environmental sensors
      • RFID tags providing information

Context sources ...

  • Reasoning the context based on fetched raw data
    • Reasoning —> process of drawing conclusions from facts
    • Context reasoning can be explained as:
      • Task of deducing new information relevant to the use of applications & users from various sources of context data
      • E.g. 30C, humid & user is stationary —> at the pool
  • Complex area with plenty of research attention

Context sources ...

  • Determine new context from known context
    • User in bed & heart rate is low –> sleeping
    • User has calendar note stating @ meeting –> @work
  • Fetch context from context broker (may have done initial processing)
    • Location provider
  • Context producers for MUPE (Multi User Publishing Environment) platform
    • Envrionment context broker
  • Standardisation immaturity

Context-aware applications

  • Behavious of App changes depending on the context
    • Location Based Services (LBS)
    • Device capability based on Apps
  • E.g.
    • Location –> Mobile phone don't ring in the bathroom
    • Activity –> Mobile phone don't ring during meeting
    • Environment –> Screen light turns on the dark / sound volume increase in nosiy place
    • Target –> Friend is online message sent via IM else via email

Uses of context data

  1. Direct use
    • Get all the context data
    • Use all data as is / infer from it meaningful context to your App
  2. Indirect use
    • Request meaningful pre-processed context data from some context producer
    • Request service adaptation data already affected by the context

Uses of context data ...

  • E.g. personal preference
  • Direct use
    • Request preference from preference broker
    • Request context from context broker
    • Infer what are the preferences for this context
  • Indirect use
    • Request preferences from preference broker
    • Preference broker requests the context from context broker
    • Preference broker deliver the context based preference

Context platform : Kontti

  • Research project on CA service platform by VTT
  • Kontti platform supports context based information sharing & context based messages
    • Used content is adapted based on user preference, device capabilities & network capabilities
  • Context
    • Time, place, social environment, technical environment, user deniable situations
    • Acquired from either user or E.g. LIF, MLP protocol for location & UAProf for device capabilities

Middleware for context-awareness

  • RCSM – Yauet al., Pervasive computing 1, 2002
  • Confab – Hong & Landay, MobiSys 2004
  • GAIA for smart spaces – Campbell et al, Univ of Illinois at Urbana-Champaign
  • CORTEX – Blair et al at Lancaster Univeristy


  • Should my service / App take context into account
    • What context are important?
  • Can I benefit on existing research on context & their meaning?
    • Activity recognition areas, colours & lightning
  • What source I can use to gain context?


  • TODO 4
    • 5 Scenarios of useful/realistic context-aware services
  • TODO 5
    • 10 Security, Privacy & Trust challenges of context-aware applications


Location Based Services (LBS)

  • Enhanced 911
  • Tourist information
  • Find nearest pub, restaurant, mall
  • Maps & guidance
  • Location based gaming
    • PacManhatann, WilMan

Types of LBS

  • User requested services
    • Location of user is provided when user requests the service
  • Triggered
    • Location of terminal is accesed from
  • Proximity
    • Proximity of the terminal is important
    • Proximity of authentication

Positioning technologies

  • Satellite based technologies (GPS, GALILEO)
    • User terminal providers the location to the service
    • Requires special receivers
      • Receiver may be external / intergrated in the terminal
  • Cell based locating
    • Location is based on the used networking technology

Positioning technologies ...

  • RF signal based locationing
    • Infrared
      • Active badge(early 1990s)
      • Transmits periodically the ID of the badge using infrared
      • Sensors in room collect the ID to determine who is in the room
  • Sound
    • Active bat (1995)
    • Active badge uses ultrasound instead of IR
    • No need for line of sight –> badge can be kept under clothing (more accurate)
  • Active floor
    • Weight sensor mats

Global Positioning Systems (GPS)

  • Operated by US millitary – opened for civilian use
  • Based on atleast 24 satellites & 5 monitoring stations
    • First launched 1978, 50 satellites launched since then
    • System maintainence ~ US$400 p.a + replacing aging satellites
  • Satellites use Intermediate Circular Orbit (ICO)
    • Each satellite circles earth twice everyday at 20200 km altitude
    • Satelites carry atomic clock
  • Ground stations measure & relay administrative data to satellites
    • This is to keep system accurate

GPS ...

  • Transmit spread spectrum signal at 2 frequencies in L-band (1.2 & 1.6 GHz)
  • Full GPS signal available for free to all users since 2000
  • General availability can be shut if US millitary sees its necessary
  • Transmission include – the time from atomic clock
  • System is used with GPS receiver that could fit to watch
  • Recievers make calculation based on signal to determine its location
    • Time is needed to calculate distance to satellite
    • Receiver needs very precise clock
    • Time for signal to travel from satellite on top of you is 1/600 s

GPS ...

  • 4 signals are needed to determine lattitude, longitude & elevation
  • Signal obstruction is problematic
    • High building cause locating problems
  • Other similar systems are:
    • GLONASS –> Russian government operated system
    • GALILEO –> EU system under construction
      • Aimed to rid of reliance of US positioning
      • After 9/11 US letter to EU opposing project i.e. millitary shutdown
      • September 2003 (China joined), July 2004 (Isreal joined)

Cellular location technologies

  1. Cell based locating
  2. Signal based locating

Cell based locating

  1. Cell based locating methods
    • In cell
    • In several cells
      • Arival on cell, parting from cell

Signal based methods

  1. Signal based methods
    • Time of arrival (TOA)
      • Distance to BS is calculated based on the time signal travels from handset to BS
    • Enhanced Observed Time Difference (E-OTD)
      • Similar to TOA but downlink is used for measuring (i.e. BS –> handset signal)
      • Location calculated at terminal
    • Time Difference Of Arrival (TDOA)
      • Requires synchronised BSs
    • Angle of Arrival (AoA)
      • Angle from which the signal arrives to mobile terminal
    • Several new methods under research

Choosing positioning technology

  • LBS service has to know the users position to provide service
    • Who provides the position to service
      • User terminal, network
  • How accurate does the position have to be?
    • Continent, Country, City, …?
    • Kilometers, 100 meters, 10 meters, cm, mm, …

Choosing positing technology ...

  • Integrated or external device
    • Specialised services users may acquire special locating technology
      • E.g. sailors, trekkers, hikker, taxi driver, pilots, …
    • External locating device can be forgotten thus preventing locating of user
    • Generic services should rely on commonly available technologies
      • I.e. locating should be integrated into commonly used devices
  • What can be required from the user?
    • Is the service targeted to small group of people or most of the people
    • Ease of use

Positioning data transmission

  • How to provide the information about position to service
    • Network provided
      • APs deliver their information about the user terminal to service
      • Service determines the location
    • Special location service determines the user location & service can request the data from it
      • Mobile Positioning Center (MPC)
      • Several posible APIs
    • Mobile device acquires the location information & provides it to service
      • E.g. GPS acquires position transmits over Bluetooth to mobile terminal which delivers it to service

Position data transmission ...

  • A notation is needed for transmitting the position information
  • Several coordinate systems
    • UTM (Universal Transverse Mercator)
      • 2D representation of earth
      • Between 84 N & 80 S latitude
    • Longitude & latitude
      • Several different systems based on longitudes & latitudes
      • WGS84 (World Geodetic System 1984)
      • Local reference system to guarantee local accuracy in certain area e.g. country
    • X & Y coordinates where origo is set on some local point such as AP
  • Several geographical shapes defining positions
    • Standardised by ISO & ETSI
    • Defines also the accuracy


    • Defined by Location Interoperability Forum (LIF)
    • Founded in 2000
    • Mobile Location Protocol
  • Independent of underlying network technology
  • HTTP used for transmission
    • Port 700 for SSL/TLS & 701 for unencrypted
    • HTTP POST for requests

API to MPC ...

  • Two types of requests
  • Immediate request
    • Response is sent right after request
  • Triggered response
    • Triggered by timer, location, mobile action
    • Can be also periodic –>results several responses
  • Non intermediate response are done using HTTP POST & reply it (Simple HTTP server)
    • Has a privacy flag
    • When privacy flag is on –> user cannot be position except during emergency

API to MPC ...

  • Support for
    • Different accuracies for location
    • Different types of location representations
    • Different coordinates
  • 4 different types of locations
    • Current, Last known, Current / Last known & Initial emergency
  • API defined in several XML DTD's
    • Transmitted data in XML form

API to MPC ...

  • WAP location framework
  • Developed by WAP forum
  • Supports WAP PUSH
  • Suits for mobile devices
  • Three different quality models
    1. Immediate query service
    2. Deffered query service
      • For periodical repsonses on terminal location
    3. Location attachment service
      • For find the nearest restaurant types of services
      • Other APIs also exist
      • E.g. Parlay API fro GSM intelligent networks

Geographic data

  • Geographic Information System (GIS)
  • Open GIS GML
    • To describe geographical information
    • Used for static representation of geography such as maps
  • POIX
    • To describe position & information related to that position
    • Interest point can be moving (e.g. you mobile device)
  • NvML
    • Express locations as points on route
  • The location data can intrude on privacy
    • What does my location tell about my behaviour?
    • Can my movements be used for blackmailing me?
    • The law in different countries vary on the status of location data
  • Use consent on use of data
    • How to get it?
    • Default policy - Use if denied, use if allowed?
  • Providing user location to third party?
  • Other way around – Enhanced 911
    • In the US law requires mobile terminal be located at certain accuracy for arriving emergency calls



  • End of WSE Lecture Series
  • Guideline
  • Polling
  • End
Last modified: 2013/07/01 14:41