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L ocation B ased S ervices for Mobile Devices

L ocation B ased S ervices for Mobile Devices. Embedded Computing Seminar Shay Horovitz. Technologies. Location Technologies. GPS - Global Positioning System AGPS - Assisted GPS Cell ID Cell ID + Timing Advance Signal Strength Based AOA - Angle Of Arrival TOA - Time Of Arrival

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L ocation B ased S ervices for Mobile Devices

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  1. Location Based ServicesforMobile Devices Embedded Computing Seminar Shay Horovitz

  2. Technologies

  3. Location Technologies • GPS - Global Positioning System • AGPS - Assisted GPS • Cell ID • Cell ID + Timing Advance • Signal Strength Based • AOA - Angle Of Arrival • TOA - Time Of Arrival • TDOA - Time Difference of Arrival • EOTD - Enhanced Observed Time Difference • Keypad based (click the address yourself) • Camera based (taking pictures of signs) • Hybrid solutions • RF Fingerprinting (on phones that will support WLAN)

  4. GPS

  5. History • Mariners relied upon the sun for latitude, and clocks for longitude • With the launch of Sputnik in 1957, radio-based global positioning became a (theoretical) possibility

  6. TRANSIT • This was a very crude form of GPS using only one satellite (1960s) • Submarines used it • Could only be used every 35-45 minutes • Submarine had to be still

  7. TIMATION (1960s) • Another satellite (TIMATION I) was launched to enhance the TRANSIT system • Major innovation was the inclusion of an atomic clock • Submarines could now be in motion and use the system

  8. NAVSTAR • In 1973, NAVSTAR began research & development • 1978 – the first 4 satellites were launched • Operated by the Department of Defense • Primary mission is to provide exact coordinates for land, sea & air-based military forces • Cost about $18,000,000,000 to develop… so far

  9. There are three components of GPS • 1.) Space (e.g. satellites) • 2.) Control (i.e. a ground station at a known geographic location) • 3.) User

  10. How it works

  11. Satellites • The GPS receiver precisely measures the time it takes a signal to travel from a satellite to the receiver • There are lots and lots of satellites • Anyone want to guess how many?

  12. Details • 6 orbital planes, included at 55 degrees to the equator, each with 4 satellites • 21 active satellites, 3 backups • Orbit the earth at 12,541 miles and have an orbital period of 11 hrs. 56 min.

  13. Satellite Triangulation

  14. How many points do you need? • Using one satellite narrows the distance to a sphere around the satellite • Using two satellites, you’ll find your location within a circle (previous slide) • Using three satellites limits your location to only 2 points • Usually, it is possible to determine which point • Using four satellites confirms your location and gives you 2 readings for altitude • Usually you can determine which is correct

  15. The importance of time • Both satellites and receivers generate Pseudo Random Noise (PRN) • A Link 1 (L1) carrier signal is generated at 1575.42 MHz and Link 2 (L2) carrier signal is generated at 1227.60 MHz • Carrier signals are modulated to produce coded signals, such as C/A code (at 1.023 MHz) and the P code (at 10.23 MHz) • The frequencies are frequency-modulated to produce step-functions • The codes repeat every millisecond • The satellites come with cesium or rubidium clocks

  16. Time lag

  17. Selective Acquisition • The US military was concerned about the possibility of terrorists or other unfriendly people using GPS to precisely guide a missile (or other unfriendly device) • The deliberately introduced errors in the time embedded in the signal • This caused locations to be up to 100m off • Turned off on 2 May 2000

  18. Selective Acquisition

  19. 2010 • GPS III system will launch • Should be even more accurate than the 8m accuracy limit currently in place

  20. Tech: AGPS • GPS has a slow time to fix unless it is permanently tracking satellites • To solve the inherent restrictions with GPS, Assisted GPS was proposed • Assisted GPS is based upon providing GPS satellite information to the handset, via the cellular network

  21. Tech: AGPS • Assisted GPS gives improvements in • Time to First Fix • Battery Life • Sensitivity • Cost • Assistance Data • Satellite Position • Time information • Visible GPS List • Sensitivity

  22. Tech: Cell ID • Cell ID: the cell that the mobile is connected to • Operator’s know where their cell sites are • Accuracy is dependent on cell density • Can be implemented both network based or device based

  23. Tech: Cell ID

  24. Tech: Cell ID + Timing Advance (TA) • TA is the time delay between the mobile and serving base station • Resolution is 500 meters • Serving cell identity and TA are available in networks

  25. Tech: Signal Strength Based • Measure signal strength from the control channels of several Base Stations • If signal levels from 3 different BSs are known, it’s possible to calculate the location

  26. Tech: Signal Strength Based

  27. Tech: AOA - Angle Of Arrival • Measure the angle of arrived signal between base station and mobile station • Location error increases as mobile is far from BSs

  28. Tech: TOA - Time Of Arrival • Measure the time of arrived signal between base station and mobile station • Mobile station locates at the intersection point which will be made by more than 3 circles

  29. Tech: TDOA – Time Difference Of Arrival • Measure the time difference of arrived signal between base station and mobile station : Minimum three base stations • Mobile station locates at the intersection point which will be made by more than 3 hyperbolas

  30. Tech: TDOA – Time Difference Of Arrival

  31. Tech: EOTD – Enhanced Observed Time Difference • Added device, LMU (Location Measurement Unit), whose location is known • LMU and mobile station measure the time difference of arrived signal from base station at the same time • Mobile station locates at the intersection point which will be made by more than 3 hyperbolas

  32. Tech: EOTD – Enhanced Observed Time Difference

  33. Tech: Keyboard Based • You set your location! • Example: Navigation Software: • Manually set origin • Manually set destination • Approve when each step is completed to get the next step instructions

  34. Tech: Camera Based • Take a picture of road signs and send by MMS to a server • 2D Barcodes

  35. Tech: Lamposts Based • Last Mile, a British company plans to offer Internet & LBS using street lampposts… • A flash memory will be installed inside the lampposts and store info about local pubs, shops. • Cost: about £500 per lamppost

  36. Tech: Hybrid Solutions Based • Improve effectiveness • Extends the coverage of a solution e.g. AGPS • Common Hybrids • EOTD / AGPS • Cell ID / AGPS • Benefits of both systems realized increasing the accuracy and availability of any single method

  37. Tech: RF Fingerprint Based • Pinpointing wireless clients makes it easier to secure and manage wireless LANs • WLANs typically have used closest access point (closest AP) or triangulation technologies to track location • RF fingerprinting improves by taking into account the effects that a building or people will have on an RF signal - characteristics such as reflection, attenuation and multi-path

  38. Tech: RF Fingerprint Based

  39. Range Of Coverage 5 m AGPS,GPS, GPS Hybrids 100 m EOTD TDOA, AOA 300 m Cell ID + TA 500 m Cell ID 1000+m

  40. Major Technologies Table

  41. Applications • Network Optimization • In-Car & Personal Navigation and wayfinding • Emergency (E911) • Monitoring traffic flow using device location & optimization • Automated Mapping • Family Tracking/ Find-A-Friend • Find the Nearest Store/place • Tourist Information/Automated Guide • Live public transport info • Games • Fleet Management • Location-based Billing • Demographic Statistics • Target Marketing • Other applications

  42. LBS based games

  43. Game: Glofun RayGun • Location: US • Target: Ghost-Hunting! • Use of GPS for location of player

  44. Game: SS+K Conqwest • Location: 5 cities in the USA • Team-based treasure hunt in the urban jungle • 5 teams searching for treasure in the form of “printed codes” – 2d barcodes that can be captured by phonecam • 1 code=1$. First team to find $5000 worth codes wins and earns a $5000 scholarship for their school…

  45. Game: Blisterent Swordfish • GPS based game • You play against a virtual school of Swordfish • See where’s the nearest school of virtual fish

  46. Game: Blisterent Torpedo Bay • A-GPS based game • No GPS reception? - Predictive positioning… • Use of real map • 360 degrees view

  47. Game: NewtGames Mogi • Location: Tokyo, Japan • GPS based • Pick up virtual items spread on the whole of Japan • At a range of 400m, you’re able to collect an item

  48. Game: Mikoishi GunSlingers • Location: Singapore • Cell-ID based • Multiplayer shooting game

  49. HP Labs City Tags • Location: Bristol, UK • iPaq PocketPC with GPS, Wifi needed • Social interaction: Tag people • When got tagged, need to find a friend to free you

  50. GeoCaching • Take something from the cache • Leave something in the cache • Write about it in the logbook

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