cellular positioning

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cellular positioning
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What is cellular positioning?

• Determining the position of a Mobile Station
  (MS), using location sensitive parameters

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Positioning Parameters

• Cell-ID
• Received Signal Strength Intensity (RSSI)
• Timing Advance (TA)
• Uplink Time (Difference) Of Arrival (TDOA)
• Downlink Observed Time Differences (E-OTD)
• Angle of Arrival (AOA)

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Triangulation

• In trigonometry and geometry, triangulation is
  the process of determining the location of a
  point by measuring angles to it from known points
  at either end of a fixed baseline, rather than
  measuring distances to the point directly. The
  point can then be fixed as the third point of a
  triangle with one known side and two known angles.

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Cell ID

• Cell identity is the most simplistic and
  cost-effective way to provide position
  information. It simply determines which cell of a
  wireless network the device is using and reports
  its location. This method typically provides
  location information accurate within a kilometer
  or two. Fortunately, there are ways to improve
  the accuracy of cell identity. Some cells are
  divided into sections, thereby reducing the total
  area of the possible location

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Cell id contin..

• To get an even more accurate reading on the
  location, a technique called timing advance (TA)
  can be used. TA provides a way to find out how
  far a user is away from the base station, thereby
  dramatically reducing the possible locations for
  that user
• When these positioning methods are combined, they
  are commonly referred to as cell global
  identity-timing advance or CGI-TA. This approach
  can yield results that are accurate within 100 to
  200 meters (100 to 200 yards).
• accuracy of CGI-TA is better in cities than in
  rural areas due to the higher density of base
  stations in populated areas

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Time of Arrival (TOA)

• Even when timing advance information is
  available, CGI-TA does not provide
  accurate-enough information for most
  location-based services. Using a time of arrival
  (TOA) approachalso known as time difference of
  arrival (TDOA). Rather than using one base
  station to determine the location, TOA uses
  information gathered from three or more base
  stations. These time differences have to be very
  accurate, requiring all of the base stations to
  be synchronized. GPS systems for synchronization
  or an atom clock.

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Time of Arrival (TOA) conted..

• Since the signal moves at a fixed speed, the
  distance of the device to the base station can be
  determined. The distance from a single base
  station does not help a lot as it is not possible
  to know in which direction the mobile user is
  moving. By using the information from three base
  stations, it is possible to triangulate the
  coordinates of the user relative to the base
  stations. TOA technology does not require any
  changes to the handset itself. The accuracy of
  this solution is fairly decent, coming in at
  around 50 meters (50 yards) in urban areas and
  150 meters (150 yards) in rural settings. TOA
  solutions are more practical on CDMA/CDMA2000
  networks, as they are already synchronized

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Angle of Arrival (AOA)

• Angle of arrival (AOA) works in a similar fashion
  to TOA, but instead of using the time it takes
  for a signal to reach three base stations, it
  uses the angle at which a device's signal arrives
  at the station. By comparing the angle-of-arrival
  data among multiple base stations (at least
  three), the relative location of a device can be
  triangulated. On its own, AOA is not commonly
  used, and is rarely discussed with LBS. That
  said, some systems may use the angle of arrival
  along with the time of arrival to get an even
  more accurate location.

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Handset-Based Solutions

• When more accuracy is needed, handset-based
  solutions are required. In these solutions the
  handset participates in the position
  determination. The accuracy of these technologies
  allows for the introduction of the third
  generation of location-based services, where
  precise location information is required.
• The two handset-based systems described next use
  similar ways of calculating location, with one
  major difference E-OTD relies on base stations
  and GPS uses satellites.

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Enhanced Observed Time Difference (E-OTD)

• Enhanced observed time difference (E-OTD)
  technology works in a similar way to time of
  arrival, but the handset makes the time
  measurements instead of the base stations. E-OTD
  relies on measuring the time at which signals
  from the base station arrive at two
  geographically dispersed locations the mobile
  device and a fixed measuring location called the
  location measuring unit (LMU). For accurate
  triangulation, at least three base stations have
  to participate in the calculation.

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E-OTD contd..

• Once the measurements are taken, the
  E-OTD-enabled handset records the time
  differences from the three base stations. The
  distance between the mobile device and the base
  stations can then be calculated by comparing the
  time differences between the timing measurements.
  The time difference can be translated into a
  distance because the signals move at a fixed
  speed. E-OTD provides an accurate and
  cost-effective way t
• o determine a mobile position. The results are
  typically accurate within 50 to 100 meters

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GPS and A-GPS

• Global Positioning System (GPS) is the most
  popular positioning technology being used today.
  It uses 24 global satellites that orbit the Earth
  to send signals to a GPS-enabled receiver. The
  receiver can communicate with three or four
  satellites at any single point in time. For this
  to work, however, there has to be a line of sight
  between the receiver and the satellites,
  precluding the use of GPSs inside buildings. In
  many product offerings, the GPS receiver is a
  separate unit that can be connected to a mobile
  device using a cable hookup or wireless
  technology such as Bluetooth. Over the past
  several years, the size, power consumption, and
  cost of GPS chipsets have fallen, leading to
  widespread use of this technology in the mobile
  environment.

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A-GPS

• One solution to both the line-of-sight and time
  delay issues is network-assisted GPS or A-GPS.
  A-GPS uses modified handsets that receive the GPS
  signals and then send those readings to a network
  server. The server uses network-based GPS
  receivers to help the handset measure the GPS
  data. The network GPS receivers are placed around
  the network several hundred kilometers apart.
  They regularly collect GPS satellite data and
  provide this data to the handsets, enabling them
  to make timing measurements without having to
  decode the actual satellite messages. This makes
  a substantial difference in the time it takes to
  get the location information. Using A-GPS, the
  time is typically between one and eight seconds

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Applications of cellular positioning

• Operator services
• Billing
• Network management
• Location based services
• Wireless Gaming

• Assistance
• Roadside assistance
• Personal or vehicle emergency
• Alarm management
• Driving Directions

• Tracking
• Tracking criminals
• Tracking external resources containers etc

• Monitoring
• Monitoring delivery process
• Fleet freight tracking
• Personal Child Security
• Mobile Worker management

• Information
• Traffic
• Nearest service
• news
• navigation help
• advertising
• Information Directory