Resources

  • Books
    • Creating Location Services for the Wireless Web - Johan Hjelm
    • Mobile Location Based Services: Professional Developer Guide - Andrew Jagoe
    • Location-Based Services - Jochen Schiller (Editor), Agnes Voisard
  • Internet

Location based services

  • Enhanced 911
  • Tourist information
  • Find nearest pub, restaurant, mall…
  • Maps and guidance
  • Location based gaming
    • PacManhattan, WilMan

Types of LBS

  • User requested services
    • The location of user is provided when user requests the service.
  • Triggered
    • The location of terminal is ac…
  • Proximity
    • The proximity of the terminal is important
    • Proximity Authentication

Positioning technologies

  • Satellite based technologies (GPS, GALILEO)
    • User terminal provides the location to the service
    • Requires special receiver
      • Receiver may be aither external or integrated in the terminal
  • Cell based locating
    • Location is based on the used networking technology
  • RF signal based locating
  • Inrared
    • Active badge (~1990)
      • Transmits periodically the ID of the badge using infrared signal
      • sensors in room collect the id to determine who are in the room
  • Sound
    • Active Bat (1995)
      • Active badge using ultrasound instead of IR.
      • No need for line of sight → badge can be kept under clothing. More accurate.
  • Active Floor

GPS (Global Positioning Sytem)

  • Operated by United States military. Opened for civilian use.
  • Is based on at least 24 satellites and 5 monitoring stations.
    • First satellite launched 1978 ,50 satellites launched since then.
    • The cost of maintaining the system is approximately US$400 million per year, including the replacement of aging satellites.
  • Satellites use Intermediate Circular Orbit (ICO)
    • Each satellite circle earth twice every day at altitude of 20200km
    • Satellites carry atomic clock
  • Ground stations measure and relay adminitrative data to satellites
    • This is to keep the system accurate.
  • Transmit spread spectrum signals at two frequencies in L-band (1.2 and 1.6 GHz)
    • Full GPS signal available for free to all users since 2000
    • General availability can be shut off if U.S. military sees it necessary
  • Transmission includes:
    • Time from the atomic clock
  • System is used with GPS receiver
    • Can be fit in e.g. watch
    • Receiver makes calculations based on the signals to determine it's location.
      • Time is needed to calculate distance to the satellite.
        • Receiver needs a very precise clock
        • Time for signal to travel from satellite on top of you is 1/600 s
    • Four signals are needed to determine latitude, longitude and elevation.
  • Signal obstruction is problem
    • high buildings cause locating problems
  • Other similar systems:
    • GLONASS (Global'naya Navigatsionnaya Sputnikovaya Sistema, Global Navigation Satellite System) which is operated by russian government
    • GALILEO , European system under construction (project started
      • Goal is to remove the reliance on United States on positioning
      • “Following the September 11, 2001 Terrorist Attack, The United States wrote to the European Union opposing the projeact, arguing that it would end the ability of the US to shut down GPS in times of military operations. ”
      • In September 2003, China joined the Galileo project
      • In July 2004, Israel signed an agreement with the EU to become a partner in the Galileo project.

Cellular technologies based locating

  • Cell based locating
    • In cell
    • In several cells
      • Arrival on cell
      • Parting from cell
  • Signals based methods
    • Time of Arrival (TOA)
      • The distance to base station is calculated based on the time signal travels from handset to base station
    • Enhanced observed time difference (E-OTD)
      • Similar to TOA but downlink is used for measuring (i.e signal from basestaion to handset)
      • Location calculated at terminal
    • Time difference of arrival (TDOA)
      • Requires synchronized basestations
    • Angle of Arrival (AoA)
      • angle from which the signal arrives to mobile terminal
    • Several new methods under research

Choosing positioning technology

  • Location based service has to know the user position, in order to provide service.
    • Who provides the position to service
      • User terminal
      • Network
  • How accurate the position has to be?
    • Continent, Country, City?
    • Kilometers, 100 meters, 10 meters, meters, centimeters?

Level 2 Headline

  • Integrated or external device?
    • Specialised services users may acquire special locating technology devices (sailors, trekkers, taxi drivers..)
    • External locationg device can be forgotten thus preventing locating of user
    • Generic services should rely on the commonly available technologies i.e. locating should be integrated in the commonly used device
  • 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 provice the information about the position to service
    • Network provides the information
      • Access points deliver their information about the user terminal to service. Service determines the location.
      • For those who have conrol on whole network
    • Special Location service determines the user location and service can request the data from it.
      • Mobile Positioning Center (MPC)
      • Several possible APIs
    • Mobile device acquires the location information and provides it to the service
    • e.g. GPS acquires position transmits over Bluetooth to mobile terminal which delivers it to service.
  • A notation is required for transmitting the position information
    • Several coordinate systems
      • UTM (Universal Transverse Mercator)
        • two dimensional representation of earth
        • between 84 N and 80 S latitudes
      • Longitude and Latitude
        • Several different systems based on longitudes and latidudes
        • WGS84 (World Geodetic System 1984)
        • Local reference system to quarantee local accuracy in certain area e.g. country
      • X and Y coordinates where origo is set on some local point such as access point
    • Several geographical shapes defining positions
      • Standardized by ISO and ETSI
      • defines also the accuracy

APIs to MPC

  • LIF API
    • Defined by Location Interoperability Forum (LIF)
    • Independent of the underlying network technology
    • HTTP is used for transmission
      • Port 700 for secure (SSL/TLS) port 701 for unencyrpted connection
      • HTTP POST is used for requests
  • 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 immediate responses are done using HTTP POST method by MSC
    • Client has to be able to handle HTTP POST and reply it (Simple HTTP server)
  • Has a privacy flag
    • When privacy flag is on, user cannot be positioned (except on emergency)
  • Supports for different accuracies for location and different types of location representations as well as different coordinations
  • Four different types of locations
    • current
    • last known
    • current or last known
    • initial emergency
  • API defined in several XML DTD's
    • Transmitted data in XML form
  • WAP Location Framework
    • Developed by WAP Forum
    • Supports WAP PUSH
    • Suits for mobile devices
    • Three different uses models

1. Immediate Query Service

2. Deferred Query Service

  • For periodical responses on terminal location

3. Location Attachment Service

  • for find the nearest restaurant types of services
  • Other API's also exist
  • e.g. Parlay API for GSM intelligent networks.

Geographic data

GIS (geographical information system) “A geographic information system (GIS) is a specialized form of an information system. In the strictest sense, it is a computer system capable of assembling, storing, manipulating, and displaying geographically-referenced information in a relational database, i.e. data identified according to their locations. Practitioners also regard the total GIS as including operating personnel and the data that go into the system.” -wikipedia

  • Open GIS GML
    • To describe Geographic information
    • used for static representation of geography such as maps
  • POIX (Point of interest exchange language)
    • Toi describe position and information related to that position
    • Interest point can be moving (e.g. your mobile device)
  • NvML
    • Express locations as points on route
  • The location data can intrude privacy
    • What does my location tell about my behaviour?
    • Can my movements be used for blackmailing?
    • The laws in different countries vary on the status of location data
  • User consent on the use of data
    • How to get?
    • default policy: Use if denied, use if allowed?
  • Providing user location to third party?
  • Other way around: Enhanced 911
    • In U.S.A law requires that mobile terminal has to be located at certain accuracy for arriving emergency calls
Last modified: 2013/07/01 14:41