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Introduction to Location-Based Service (LBS)

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1. Location-Based Services/Applications …

1. Location-Based Services/Applications
2. Enhanced Cell Identity (E-CID)
3. Assisted GPS (A-GPS)
4. Uplink Time Difference of Arrival (U-TDOA)
5. Matrix
5. Angle of Arrival (AOA)

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  • 1. Introduction toIntroduction to Location Based ServicesLocation Based Services Yi-Hsueh Tsai Institute for Information Industry (III)
  • 2. OutlineOutline 1. Location-Based Services/Applications 2. Enhanced Cell Identity (E-CID) 3. Assisted GPS (A-GPS) 4. Uplink Time Difference of Arrival (U- TDOA) 5. Matrix 6. Angle of Arrival (AOA)
  • 3. Location-Based Services/ApplicationsLocation-Based Services/Applications  There is no single mobile locating method that is best suited to all LBS and applications, but by having the broadest selection of locating options deployable in one system, operators can realize the most effective cost/performance relationship.  LBS applications and services are best supported by location systems that accommodate their strikingly different requirements.
  • 4. Location-Based Services/ApplicationsLocation-Based Services/Applications  Three generic categories of location-based applications: – Public Safety – Security – Commercial Location-Based Services  Public safety services like the provision of 112 and 911 caller location information to emergency service centers  Security applications
  • 5. Location-Based Services/ApplicationsLocation-Based Services/Applications  Commercial LBS may include: – Child locator – Boundary maintenance – Service personnel locator – Enhanced dispatch – Delivery vehicle locator – Package or shipment locator – Roadside assistance – Driving directions
  • 6. Enhanced Cell Identity (E-CID)Enhanced Cell Identity (E-CID)  E-CID uses the combination of CID/sector (Cell Identity) and TA/NMR (Timing Advance/Network Measurement Report) information to calculate mobile locations with better accuracy than CID alone.  Attainable accuracy with E-CID is highly dependent on the density of base station sites (accuracy increases with density).
  • 7. Enhanced Cell Identity (E-CID)Enhanced Cell Identity (E-CID)  In urban networks where base station sites are closely spaced, E-CID can deliver accuracy within a tolerance of several hundred meters.  In rural networks, however, where cells can be widely separated, E-CID accuracy error can range to several kilometers.
  • 8. Advantages and Limitations: E-CIDAdvantages and Limitations: E-CID  Advantages – Very Low Cost – Works with all Mobiles – High Yield, Low Latency – High capacity  Limitations – Accuracy subject to wide variation depending on BTS site density
  • 9. Assisted GPS (A-GPS)Assisted GPS (A-GPS)
  • 10. Assisted GPS (A-GPS)Assisted GPS (A-GPS)  A-GPS is a handset-based mobile locating method fundamentally based on GPS locating technology but functionally distributed between the mobile and a centralized server.  Mobiles must be specially equipped to receive GPS signals from multiple GPS satellites in order to make measurements of the signals from GPS satellites and relay this information or their calculated position through the mobile network to the SMLC/SAS/SLP software (iSAS: Control Plane, SUPL: User Plane implementations).
  • 11. Assisted GPS (A-GPS)Assisted GPS (A-GPS)  In cases where the mobile does not compute its own location from GPS data, the SMLC/SAS/SLP uses GPS data relayed from the target mobile to compute the mobile's position.  Once determined, the position can be sent to a gateway mobile location center (GMLC) or SUPL Location Platform (SLP) for distribution to the application that originated the location request.
  • 12. Assisted GPS (A-GPS)Assisted GPS (A-GPS)  A-GPS is a supplemental form of GPS whereby GPS satellite position data is sent from the SMLC/SAS/SLP through the mobile network to the mobile to assist the mobile in determining which GPS satellites it should attempt to acquire.  This supplemental data is intended to: – Speed the mobile's satellite signal acquisition proces. – Increase the mobile's ability to receive signals from the target GPS satellites.
  • 13. Assisted GPS (A-GPS)Assisted GPS (A-GPS)  A-GPS is intended to reduce latency and improve other location performance when a mobile's view of GPS satellites is obscured. That can occur when the caller is in a building, in a vehicle, or in an "urban canyon.“  Although A-GPS does improve overall locating performance, accuracy, latency, and yield performance can be subject to degradation if a mobile's view of GPS satellites is obscured.
  • 14. Assisted GPS (A-GPS)Assisted GPS (A-GPS)  A-GPS has been used in public safety and commercial applications in CDMA networks where it has been supplemented with AFLT (Advanced Forward Link Trilateration) to enhance location reliability.  Since AFLT requires the underlying mobile network to be synchronous, AFLT is not available for wireless networks other than CDMA. Geometrix MLC offers the option of Enhanced CID (using TA/NMR) for GSM network applications as a supplement to A- GPS.
  • 15. Advantages and Limitations: A-GPSAdvantages and Limitations: A-GPS  Advantages – Accurate – Lower infrastructure costs – Costs can be spread over time Some costs are passed on to users when they buy the required mobiles – High scalability  Limitations – Handset-based; requires specially-equipped mobiles – Can encounter GPS signal reception problems indoors, in vehicles, and in "urban Canyons" – Subject to accuracy and yield performance degradation when view of GPS satellites is obscured
  • 16. Uplink Time Difference of Arrival (U-TDOA)Uplink Time Difference of Arrival (U-TDOA)
  • 17. Uplink Time Difference of Arrival (U-TDOA)Uplink Time Difference of Arrival (U-TDOA)  U-TDOA is a network-based means of determining a mobile's position by comparing and calculating the difference in time required for a mobile's signal to reach different BTS sites.  The arrival time measurements are made by location measurement units (LMUs) installed at selected BTS sites (one LMU per selected site).
  • 18. Uplink Time Difference of Arrival (U-TDOA)Uplink Time Difference of Arrival (U-TDOA)  The LMUs forward the signal arrival time measurements to the SMLC/SAS serving mobile location center (SMLC).  The SMLC then calculates the mobile's position. U-TDOA requires that the target mobile's signal can be measured by at least three LMUs. Geometrix MLC LMUs use sophisticated signal processing to increase their sensitivity in measuring signals from very distant mobiles.
  • 19. Uplink Time Difference of Arrival (U-Uplink Time Difference of Arrival (U- TDOA)TDOA) 1. Location request originated by MSC or LBS application 2. SMLC initiates request to appropriate LMUs to measure signal TOAs from target mobile 3. LMUs measure TOA from target mobile, forward measurements to SMLC 4. SMLC calculates mobile's position 5. Location Center forwards position data to GMLC (through BSC and MSC) 6. GMLC forwards position data to LBS application
  • 20. Advantages and Limitations: U-TDOAAdvantages and Limitations: U-TDOA  Advantages – Accurate – Works with existing mobiles (no need for user upgrades) Accuracy, yield, and latency performance maintained indoors and in vehicles  Limitations – LMUs required, higher infrastructure expense – More difficult to obtain full coverage in mountainous areas with thinly deployed BTS sites – Lower scalability
  • 21. MatrixMatrix
  • 22. MatrixMatrix  Matrix is a mobile locating method whereby SMLC/SAS serving mobile location center (SMLC) with Matrix software computes the position of a mobile based on the arrival time of synchronization burst signals from multiple BTSs as received and measured at the target mobile.  The target mobile sends these measurements through the wireless network to the SMLC/SASSMLC.
  • 23. MatrixMatrix  The SMLC/SAS calculates the target mobile's position using time of arrival difference principles.  An early form of enhanced observed time difference (E-OTD) required special location measurement units (LMUs) at BTS sites to establish a common time reference (necessary since GSM networks are not synchronous).
  • 24. MatrixMatrix  Matrix might not require such LMUs since it may use a common time reference established by means of time of arrival (TOA) measurements of the BTS synch signals at multiple mobiles in the area.  Those mobiles send the measurements to the SMLC/SAS where they are used to calculate a time reference grid, or Matrix.  Matrix requires that a target mobile be able to receive and measure burst synchronization signals from at least three separate BTS sites.
  • 25. MatrixMatrix 1. Location request originated by MSC or LBS application 2. SMLC initiates request to target mobile to make E- OTD measurements 3. Mobile measures arrival times of synch. burst signals from multiple BTS sites (3-8 sites), calculates arrival time differences (E-OTD) 4. Mobile sends E-OTD data to SMLC 5. SMLC calculates mobile's position 6. Location Center sends position data to GMLC (through BSC and MSC) 7. GMLC sends position data to LBS application
  • 26. Advantages and Limitations: MatrixAdvantages and Limitations: Matrix  Advantages – Accurate – Moderate Cost – Can be complementary to U-TDOA  Limitations – Requires mobiles to be equipped with E-OTD software – Mobiles must receive signals from at least three BTS sites
  • 27. Angle of Arrival (AOA)Angle of Arrival (AOA)
  • 28. Angle of Arrival (AOA)Angle of Arrival (AOA)  AOA is a network-based means of determining the position of a mobile by establishing lines of bearing from BTS sites to the mobile.  AOA requires the installation of a location measurement unit (LMU) at each AOA- equipped base station site, as well as special direction-sensing antennas.  AOA is generally deployed only in very limited, especially challenging circumstances.
  • 29. Angle of Arrival (AOA)Angle of Arrival (AOA)  For example, AOA is sometimes used in mountainous areas with sparse base station installations and challenging site-to-site geometry.  While AOA is available to meet very challenging public safety and/or security applications, Andrew does not anticipate that operators will use AOA to support commercial GSM location-based services.
  • 30. Advantages and Limitations: AOAAdvantages and Limitations: AOA  Advantages – Accurate – Works with existing mobiles – Can supplement U-TDOA in very mountainous, sparse base station areas  Limitations – LMUs required, higher infrastructure expense – Implementation costs are up-front – Requires special antennas at BTS sites – Lower scalability

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