Tracking And Positioning Of Mobile Systems In Telecommunication Networks

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Tracking And Positioning Of Mobile Systems In
Telecommunication Networks

• Presented By
• RUTUJA .V. SHEDSALE
• MTECH(ETC)-102151014

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NEED FOR TRACKING

• Emergency service for subscriber safety.  
• Location sensitive billing.
• Cellular Fraud detection.
• Intelligent transport system services.
• Efficient and effective network performance
• and management.

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Configuration of a typical mobile
telecommunication network.
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INTRODUCTION TO MOBILE TECHNOLOGY

• Whole service area is divided into several
  coverage areas known as a cell.Each area has a
  separate base station(BS).
• Every BS is provided with a frequency of range
  450 to 900 MHz.
• The MTSO controls the BSs so that the subscriber
  can continue his call without interruption.
• Tracking the location within the boundary of a
  cell in a telecommunication network is known as
  location based services.
• Mobile Technology includes mainly two functions
  namely call fixing and hands off process.
• Call fixing is process of connecting a call.
• Hands off is changing the BS frequency of the
  user.

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ARCHITECTURE OF A GEOLOCATION SYSTEM

• A geolocation service provider provides
• location information and location aware
• sevices to subscribers.
• The service provider will contact the
• location control center about the coordinates
• of the mobile system (MS).
• The location control center will gather
• information required to compute the MSs
• location.
• The service provider will then use this
• information to visually display the MSs
• location to the subscriber.
• The subscriber can be the MS itself.

GEOLOCATION SYSTEM ARCHITECTURE K0S00
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PSAP trying to answer an E-911 call
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TECHNOLOGIES USED FOR GEOLOCATION

• 1.HANDSET BASED MOBILE POSITIONING AND TRACKING
• 1.1 GLOBAL POSITIONING SYSTEM (GPS)
• 2. DIRECTION BASED GEOLOCATION
• 2.1 ANGLE OF ARRIVAL METHOD
• 3. DISTANCE BASED POSITIONING
• 3.1 TIME OF ARRIVAL(TOA)
• 3.2 TIME DIFFERENCE OF ARRIVAL(TDOA)
• 4. LOCATION TRACKING CURVE METHOD

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GLOBLE POSITIONING SYSTEM (GPS)

• To locate the mobile telephone by itself, the
  mobile telephone is provided with a GPS receiver
  to calculate its location.
• There should be an unobstructed line of sight to
  four or more GPS satellites.
• GPS satellites broadcast signals from space,
  which each GPS receiver uses to calculate its
  three-dimensional location (latitude, longitude,
  and altitude) plus the current time
• GPS receivers are used in mobile phones,
  vehicles, marine navigation devices and military
  applications.

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Encoding And Modulation

• The navigational signals transmitted by GPS
  satellites encode a variety of information
  including satellite positions, the state of the
  internal clocks, and the health of the network.
  Message is send at a rate of 50 bits per second.
• The first part of the message encodes the week
  number and the time within the week, as well as
  the data about the health of the satellite. The
  second part of the message, the ephemeris,
  provides the precise orbit for the satellite. The
  last part of the message, the almanac, contains
  coarse orbit and status information for all
  satellites in the network as well as data related
  to error correction.
• These signals are transmitted on two separate
  carrier frequencies 1.57542 GHz (L1 signal) and
  1.2276 GHz (L2 signal),that are common to all
  satellites in the network.
• The satellite network uses a CDMA spread-spectrum
  technique where the low-bitrate message data is
  encoded with a high-rate pseudorandom(PRN)
  sequence that is different for each satellite.

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Demodulation and Decoding

• Since all of the satellite signals are modulated
  onto the same L1 carrier frequency, there is a
  need to separate the signals after demodulation.
  Demodulating and Decoding of GPS Satellite
  Signals takes place using the Gold codes.
• This is done by assigning each satellite a unique
  binary sequence known as a Gold code. The signals
  are decoded, after demodulation, using addition
  of the Gold codes corresponding to the satellites
  monitored by the receiver.

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Position calculation in GPS

• Using messages received from a minimum of four
  visible satellites, a GPS receiver is able to
  determine the times sent and then the satellite
  positions.
• The x, y, and z components of position, and the
  time sent, are designated as where the subscript
  i is the satellite number and has the value 1, 2,
  3, or 4.
• The GPS receiver can compute the transit time of
  the message as (tr-ti) .The distance traveled or
  pseudorange, can be computed as (tr-ti)c .
• A satellite's position and pseudorange define a
  sphere, centered on the satellite with radius
  equal to the pseudorange.
• The position of the receiver is somewhere on the
  surface of this sphere.
• Thus with four satellites, the indicated position
  of the GPS receiver is at or near the
  intersection of the surfaces of four spheres.

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APPLICATIONS OF GPS
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ANGLE OF ARRIVAL METHOD

• This method calculates the angle of arrival of
  signal receiving at the BS.
• When a mobile user switches the system ON it
  receives the signal from different base stations,
  may be 3 or 4 or more. The angle of arrival
  method requires two or more base station for the
  determination.
• It measures the direction of signal falling on
  the base station and measures the angle of
  incidence with respect to a normal and determines
  the position of the system.
• Angle of arrival method is not an accurate method
  used for the mobile positioning because of its
  some disadvantages such as atmospheric particles,
  scattering etc.

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DISTANCE BASED POSITIONING-TOA METHOD

• The TOA method calculates the distance of a
  mobile telephone and a BS based on the TOA of a
  signal transmitted from the mobile telephone at
  the BS.
• It is assumed that the mobile telephone is
  located at the intersection point of three
  circles having the radius of the distances
  between the BSs and the mobile telephone.
• The distance is calculated by the following
  equation,
• Ri C ti sqrt ( (xi X ) 2 (yi Y) 2 )
  where,
• C Propagation speed of electromagnetic wave,
• ti propagation of time from the mobile
  telephone to ith base station,
• Xi, yi -- location of ith base station,
• X, Y mobile position

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DISTANCE BASED POSITIONING-TDOA METHOD

• The time-difference-of-arrival (TDOA) assumes
  that the mobile is located at the intersection
  point of atleast 3 hyperbolas.
• The time difference between the received signals
  to base stations of a certain subscriber is found
  using the generalized cross correlation method.
• The resulting hyperbolic equations can be solved
  for finding the position location (PL) of a
  certain subscriber.

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LOCATION TRACKING CURVE METHOD
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Description

• The location data processor draws two circles C1
  and C2 with their respective centers set at BSs
  T1 and T2 based on the TOAs of a signal
  transmitted from the corresponding mobile
  telephone M1 or M2 to the two BSs T1 and T2
  located near the mobile telephone M1 or M2. The
  two circles C1 and C2 define a common chord L1.
• Therefore, we use location tracking curves TR1
  and TR2 connecting the same two intersection
  points P1 and P2 of the two circles C1 and C2,
  instead of the common chord L1.
• The two curves TR1 and TR2 have their middle
  points intersecting the line ST, which connects
  the positions of the two BSs T1 and T2 and the
  parts of two circles C1 and C2 drawn to connect
  the two intersection points P1 and P2.
• This method prevents the location error caused by
  the multi-path fading or the NLOS path
  characteristics.

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Determination of the location tracking curve

• Assuming that the first and the second BSs T1 and
  T2 selected for use in the location tracking are
  present at positions (x1, y1) and (x2, y2),
  respectively, the location data processor draws
  the two circles C1 and C2 with the coordinates
  (x1, y1) and (x2, y2) of the two BSs T1 and T2 at
  their centers
• The curve connects the two points P1 and P2 at
  which the two circles C1 and C2 intersect each
  other. The coordinates of the intersection points
  P1 and P2 are (xA, yA) and (xB, yB),
  respectively.
• Reference circles TR1 to TR4 are drawn with
  respect to the second BS T2 with smaller variances

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Reference circle selection

• The variances of the TOAs of a signal which
  arrives at the two BSs T1 and T2 from different
  paths are used to find the curve on which the
  actual location of the mobile telephone is
  determined.
• The location data processor compares the
  variances calculated by the first BS T1 with the
  variances calculated by the second BS T2 and
  considers that the mobile telephone is near to
  that BS with the larger variances and selects the
  BS with smaller variances as a reference point to
  draw the reference circle.
• The location data processor compares the
  variances calculated by the two BSs T1 and T2 and
  selects the base station with smaller variances
  as a reference point to draw the refer
• If the selected variances (those of the second BS
  T2) are s, the location data processor compares
  the selected variances s, with the preset
  reference variances s 1, s 2, and s 3.
• The location data processor selects the optimal
  curve (reference circle) for the two BSs among
  the several BSs, and selects another optimal
  circle for another BS pair, and so on.

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FINAL POSITIONING OF MOBILE

• When curves are selected for all selected BS
  pairs, the location data processor obtains the
  intersection points among the selected curves.
• As the selected curves do not intersect at one
  point due to the multi-path fading or the NLOS
  effects, the midpoint of these intersection
  points is determined as the location of the
  mobile telephone.
• The location data processor represents the
  intersection points in the latitude and the
  longitude coordinates and transmits the position
  coordinates to the network and the mobile
  telephone.

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SUMMARY

• Our proposal is advantageous in that the location
  of a mobile telephone can be accurately tracked
  even in the multi-path fading and the NLOS
  environment, by using more accurate tracking
  curves connecting the intersection points among
  circles.
• We have described about accurate positioning of
  mobile telephones, which can be used for several
  applications.
• The important considerations to be undertaken
  while selecting a location based technology are
  location accuracy, implementation cost,
  reliability, increasing functionality.

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THANK YOU