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Positioning in Location Based Services


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This presentation describes positioning techniques for Location Based Services.

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Positioning in Location Based Services

  1. 1. Positioning<br />MARK ESSIEN<br />11.11.2009<br />1<br />
  2. 2. Table of Contents<br />Table of Contents<br /><ul><li>Introduction</li></ul>A quick overview of positioning systems<br /><ul><li>Satellite Based Positioning</li></ul>Positioning with GPS<br /><ul><li>Network Based Positioning</li></ul>GSM and Wireless LAN based positioning techniques<br /><ul><li>Indoor Positioning</li></ul>Infrared, Radio, Ultrasound, and Video based techniques<br /><ul><li>Conclusion and Future Perspectives</li></ul>1<br />2<br />3<br />4<br />5<br />2<br />
  4. 4. What are positioning systems?<br />These are systems that allow us detect the location of a person or object.<br />4<br />There are lots of different such systems in different areas. Here we will talk about the systems we need for Location Based Services.<br />
  5. 5. 5<br />Such as:<br />Indoor Positioning Systems<br />Network Based<br />Positioning Systems<br />Satellite Positioning Systems<br />
  6. 6. How do we do get locations?<br />6<br />Sensor Network tracks the device<br />Device discovers its own position<br />
  7. 7. Basic techniques to discover locations<br />7<br />Cell of Origin<br />
  8. 8. Basic techniques to discover locations<br />8<br />Time of Arrival<br />
  9. 9. Basic techniques to discover locations<br />9<br />Angle of Arrival<br />
  10. 10. Basic techniques to discover locations<br />10<br />Measuring<br />Strength<br />
  11. 11. Basic techniques to discover locations<br />11<br />Processing Video Data<br />
  12. 12. 12<br />Satellite Positioning<br />2<br />
  13. 13. Advantages<br />13<br /><ul><li>Can be used anywhere on earth
  14. 14. Not disturbed by enviromental conditions
  15. 15. Precise</li></ul>Disadvantages<br /><ul><li>Expensive to launch satellite
  16. 16. Cannot position indoors</li></li></ul><li>Basic Mechanism of Satellite Navigation<br />14<br />The user knows the distance of the satellite to him, as well as the position of the satellite<br />So he can calculate a radius is somewhere on. But he does not know where on the radius he is.<br />
  17. 17. Basic Mechanism of Satellite Navigation<br />15<br />By looking at the intersection of the coverage radius of at least 3 satellites, he can discover his exact position<br />
  18. 18. How does the device know the position of the satellite?<br />Satellites are on fixed, known orbits. <br />Additionally, the position of all satellites is updated by sending a so-called almanac with currrent position information to the device.<br />(By the way, if you don’t use your GPS device for a long time, it needs to download this almanac, which is why it takes much longer to start)<br />16<br />
  19. 19. What about the distance r from the satellite?<br />17<br />r = c * t<br />r = Distance from Satellite<br />c = Speed of Light<br />t = Time it took signal to reach device<br />
  20. 20. Problems<br />The speedoflightisveryhigh. An errorof1 μs leadsto a 300m inaccuracy<br />Satelliteshaveatomicclocks, and so theirtimesareveryaccurate, but thedevices do not. The clocksarehence not synchronised.<br />Tocorrecttheunknownfactor, a fourthsatellitesignalisdrawn in, andequationsthatfactor in the time offsetbuilt<br />These non-linear equationscanbecalculatedusing Kalman filtersor Taylor series<br />18<br />
  21. 21. Global Positioning System<br />19<br /><ul><li>A system of 21 to 30 satellites in orbit around the earth and providing positioning</li></ul>Information.<br /><ul><li> Conceived in 1970, satellites launched in 1984, 12 working satellites by 1990
  22. 22. Full operational capability in July, 1995
  23. 23. Made up of 3 segments</li></li></ul><li>Space Segment / The GPS Satellite<br />20<br /><ul><li> Weighs between 1.5 and 2 tons
  24. 24. Energy supplied by solar cells
  25. 25. Central computer is a 16 Mhz CPU
  26. 26. Expected lifetime of 7.5 years
  27. 27. 12 hours for an orbit
  28. 28. 60 days to launch after failure
  29. 29. Programmed in ADA
  30. 30. About 25.000 lines of code. In comparison,Microsoft Office has 30 million lines of code.</li></ul>-<br />
  31. 31. User Segment / The GPS receiver<br />21<br />
  32. 32. Control Segment /GPS Master Control Station<br />22<br />Schriever Air Force Base, near Colorado Springs, U.S.A<br />
  33. 33. GPS Properties<br />SPS (Standard Positioning Service): Available for civilian users – Less Accurate (100m horizontal)<br />PPS (Precise Positioning Service): 22m horizontal. For military use<br />Data channel with 50bps<br />23<br />
  34. 34. GPS Accuracy<br />Accuracy affected by clock errors, fluctuation in<br />satellite orbit, disturbances of the<br />atmosphere/ionosphere and multipath errors<br />24<br />
  35. 35. Improving GPS accuracy with DGPS<br />25<br />DGPS involves a system of base stations with fixed, known positions that broadcast<br />correctional information to the devices directly.<br />
  36. 36. Correction Stations in Australia<br />26<br />AMSA&apos;s Differential Global Positioning System provides a network of radio beacons that <br />improve the accuracy and integrity of the Global Positioning System (GPS) around selected <br />areas of Australia&apos;s coast.<br />
  37. 37. Improving GPS accuracy with WAAS<br />Base stations calculate correction data, then transmit it to geostationary satellites, who then pass it on to the devices<br />27<br />
  38. 38. Selective Availability<br />Artificial Distortion of GPS signal by U.S government<br />Switched off in 2000<br />New Satellites being launched 2009 do not have this capability any more<br />28<br />
  39. 39. Other Satellite Based Navigation Systems<br />29<br /><ul><li>Abandoned in 2007 by industry, taken over by EU
  40. 40. Slated for operation start by 2013
  41. 41. Bases in Germany and Italy
  42. 42. Partners include China, Israel, Ukraine, Morroco, South Korea
  43. 43. GLONASS – Russian alternative to GPS
  44. 44. Launched in 1996
  45. 45. Financial problems, only 10 satellites by 2000
  46. 46. Partnership with India, 12 satellites added by 2008</li></li></ul><li>30<br />Network Based Positioning<br />3<br />
  47. 47. Network Based Positioning<br />Using existing networks for positioning<br />31<br />Wireless LAN networks<br />The GSM network<br />
  48. 48. Already covers a wide area<br />User knows his position already, based off the cell he is in<br />However, cell accuracy from 1km to 35km, so very inaccurate<br />32<br />Overview<br />
  49. 49. Sony Ericsson developed the MPS (Mobile<br />Positioning System) that improves the accuracy.<br />It does so using multiple methods.<br />Detect Cell<br />Detect the segment antennae user is, allowing an angle of antennae to user<br />Use Timing Advance to determine distance. Accuracy is circa 555m<br />Signal runtimes to 4 base stations<br />33<br />Improving Accuracy<br />
  50. 50. Position can be detected by measuring signal strength of all wireless LAN access points<br />Requires a training phase where the locations are mapped to signal strengths<br />Realized as prototype by Microsoft, as well as with the Nibble system<br />Outdoor variant in use in the iPhone 2G, using a service by the company SkyHook<br />34<br />WLAN: Overview<br />
  51. 51. Skyhook<br />35<br /><ul><li>Used in iPhone 2G to discover the location of users even withouta GPS radio
  52. 52. Reasonable accurate
  53. 53. Company drives around in metroareas and maps available wirelessLAN devices and signal strengths</li></ul>to the GPS location<br />
  54. 54. Coverage (Skyhook)<br />36<br />
  55. 55. 37<br />Indoor Positioning<br />4<br />
  56. 56. Indoor Positioning<br />Indoor positioning does not work with satellites<br />because the radio signals do not penetrate the<br />walls. So other systems are required. The indoor positioning devices can be split up into categories based on the technology in use:<br />38<br />Infrared<br />Radio<br />Ultrasound<br />Video<br />
  57. 57. 1. Infrared Beacons<br />Infrared devices are cheap and easy to get, and so are often used for indoor<br />positioning. Two sample system are the Active Badge System and the Wireless<br />Indoor Positioning System (WIPS).<br />39<br />
  58. 58. The Active Badge System<br />Every user carries a transmitter in the shape of a card<br />Infrared signal with pulse length 0.1s is sent every 15 seconds<br />Signal identifies user with unique code<br />Low cost with a long battery life<br />40<br />
  59. 59. Active Badge: Technology<br />41<br /><ul><li>Signals do not penetrate walls, but rather reflect of walls, so can receive signals even without line of sight
  60. 60. Signals flood room, so positioning is accurate to room level
  61. 61. Long battery life because the pulse duration very short compared to idle time
  62. 62. Signals do not collide because of low differences in pulse duration</li></li></ul><li>2. Radio Beacons<br />Using radio, time of arrival as well as signal strength methods<br />can be used to compute positions in buildings (in a manner<br />similar to satellites). Positioning in 3 dimensions becomes<br />possible if transmitters are on multiple floors.<br />42<br />
  63. 63. The SpotON System <br />Uses the strength of the signals at the spot from where the measurement occurs<br />The signal strength is assumed to decrease with the square of the distance. This is not always the case, however, as there may be obstacles.<br />Accuracy of 3m can be achieved with this<br />43<br />
  64. 64. RFID<br />Small systems with processor, memory, antennae, but without power supply<br />Use the energy from the radio waves<br />Distance of 1 meter<br />Often used to track objects – can be used to find out if an object has passed a certain point<br />44<br />
  65. 65. 3. Ultrasound<br />45<br />Ultrasound devices use ultra<br />sound transmitters to transmit<br />the position of a user. Sensors<br />are placed in the building, and<br />the transmitter sends ultra<br />sound signals on request. <br />
  66. 66. The Active Bat System<br />46<br /><ul><li>The server transmits a send request by radio to the so-called “Bat”. A specific Bat is always chosen to avoid collisions
  67. 67. The bat replies with an ultra-sonic impulse
  68. 68. Receivers on the ceiling, which are spread out at 1.2m intervals, receive the signal
  69. 69. The receivers pass the signals on to a location server via a wired network
  70. 70. Position is calculated similar to satellite positioning – non-linear system of equations using signal runtimes. Runtimes of ultrasound are much lower than for radio signals, leading to simpler calculations</li></li></ul><li>4. Video Based Systems<br />47<br />Indoor positioning can<br />also be achieved by<br />capturing and<br />processing video data to<br />recognize and position<br />objects. This method is<br />computing intensive.<br />
  71. 71. Using Visual Tags<br />48<br /><ul><li>The evaluation of the video data can be simplified with the use of visual tags
  72. 72. The tags can store information, for example by the position of squares to each other
  73. 73. The size of the tag can be used as a reference for the distance of the user to the camera</li></li></ul><li>Positioning<br />If two cameras detect the same tag, they can<br />pinpoint the users location using triangulation<br />49<br />
  74. 74. 50<br />Conclusions & Perspectives<br />5<br />
  75. 75. Conclusion<br />In conclusion, positioning is an important<br />technology that is of critical importance in<br />location based systems. We have gone through<br />the most important methods in this<br />presentation, and imparted an understanding of<br />how modern positioning works.<br />51<br />
  76. 76. Future of positioning<br />There are still a lot of problems left in the positioning<br />area. In particular:<br />The speed of position detection can be improved<br />Power consumption issues should be solved<br />Accuracy should get better, independent of the location<br />Ideal positioning systems should combine the different methods available<br />52<br />
  77. 77. Thank you<br /><br />
  78. 78. References<br />Data CollectionJörg RothIn Jochen Schiller, AgnèsVoisard (eds), Location-Based Services, Morgan Kaufmann Publishers, May 2004<br />Positioning Systems Jörg RothChapter 3 of the thesis &quot;A Decentralized Location Service Providing Semantic Locations“ (habilitation), 2005<br />Fact Sheet: Differential Global Positioning System (DGPS) Australian Maritime Safety Authority Canberra, ACT Australia August 2007<br />Website: How it Works – Skyhook Wireless: 11.11.2009<br />Website: Glonass Official page: Accessed 11.11.2009<br />Website: Galileo: 11.11.2009<br />54<br />