Mobile Positioning Solutions for GSM

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• Mobile Positioning Solutions for GSM
• Dirk NikolaiAlcatel RI Stuttgart
• January 11th, 2002

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Definition of mobile Location Services(LCS)
Network-based services thatintegrate a derived
estimate ofa mobile device's location or
positionwith other informationso as to provide
added value to the user.
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Family of Location Services
Range of applications
Assistance Personal or vehicle emergency,roadside
assistance,alarm management
Information Entertainment, news, weather,traffic
navigation,advertising, find your friend
Network related Network management,billing,
customer care.
Asset tracking Wireless remotemanagement
control
B2B Fleet freight tracking M2M P2P
C2CPulled info.Find friend, pets P2P
B2C Pushed info.Discount, ad, special
event M2P
C2B Pulled info. Find Gas station, restaurant,
P2M
B Business C Consumer M Machine P Person
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Expected RevenuesAn emerging, but uncertain
Market!
Ovum
Strategis Group
Localised Services
Bio 15.9
Billing
Bio 1.9
Bio 13.5
Information
Bio 1.7
Roadside assistance
Bio 1.6
Traffic navigation
M-Commerce
Bio 1.1
Bio 2.1
Advertising
Bio 5
Bio 32.7
2005 EU operator revenues
Bio 11
Y00-Y05 cumulated revenues
Bio 81.9
Discrepancies Service definition, penetration
rate, number of requests, various sources of
revenues
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Positioning technologies Cell based methods

• Cell-Identifier (CI) based, refined by Timing
  Advance (TA)

• Enhancement usage of received signal levels
  (RXLEV in NMR) - refine and add reliability to
  position

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4
2
3
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Positioning Technologies Trilateration time
differences in network

• In existing GSM networks BTSs are not
  synchronized (RTD ? 0)
• Position calculation via hyperbolic trilateration
  between BTS pairs

RTD
GTD OTD RTD
RTD Real Time Difference OTD Observed Time
Difference GTD Geometric Time Difference
? OTD
GTD 0
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Positioning Technologies Trilateration

• Measurement of Observed Time Difference between 3
  BTS

• Two types of Location Measurement Units (LMU) are
  foreseen in the standard
• Type A, stand-alone
• Type B, integrated in the BTS
• LMU can be avoided by synchronizing BTSs with GPS
  or by time-stamping DL emissions

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Positioning technologies Assisted GNSS

• Integration of GNSS (GPS) receiver in the handset
  
• Assistance data sent through RAN ephemeris,
  clock information, differential corrections
• Enhance accuracy, integrity, time-to-first-fix,
  increase battery life...

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Positioning technologies Technologies comparison
Complexity / Investment
High
Assisted GNSS
Handset HW costly modification Indoor coverage
problem
E-OTD
Network costly HW impact new SW in handset
OTDOA
CELL-ID TA NMR
Low
Accuracy
Low
High
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Network Based Positioning Methods

• Network Based Positioning
• allows to locate legacy handsets (100
  penetration)
• supplementary solution to GNSS positioning
• Candidates for Cell-Identity-based Positioning
  (CI, CI)
• Cell-ID only (geographical coordinates of serving
  cell) ? CI
• Cell-ID and Timing Advance ? CITA
• Cell-ID, Timing Advance and received signals
  level (RXLEV) ? CITANMR (network measurement
  report)
• Distance Calculation Method (DCM)
• Field Strength Mapping (FSM)
• Advanced Calculation Methods (ACM)

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Positioning Method CITA

• Cell-Identity and Timing Advance
• TA gives a distance estimate between the BTS and
  the MS
• straight TA-distance (TA-value ½)
  dTA dTA ½ 3.69?s symbol period 3e8 m/s
  554m
• Easy to implement
• Omnidirectional cells estimated position BTS
  position
• Sectored cells estimated position intersection
  of antennaazimuth and TA-distance

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Positioning Method CITANMRDistance Calculation
Method (DCM)

• Cell-Identity, Timing Advance and Measurement
  Report (NMR)
• NMR contains measured RX levels from serving cell
  and neighbouring cell(s)
• Modelling of propagation loss Hatas Formula L
  A B log10(d/km)
• L decibel path loss
• A offset loss
• B distance exponential
• Calculate distance d to BTSs based on measured
  path loss L d/km 10((L A) / B)
• Contours are circles (per BTS sector)

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Distance Calculation Method (DCM)Illustration of
Position Calculation
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Distance Calculation Method (DCM)Data from
Measurements

• Comparison of Hatas path loss formula with field
  data

"good"
bad
? standard deviation in the range of 1020 dB !
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Positioning Method CITANMRField Strength
Mapping (FSM)

• Cell-Identity, Timing Advance and Measurement
  Report (NMR)
• Cellular area is splitted in pixels (e.g. 50m x
  50m) for which received levels of surrounding
  cells are predicted
• Usage of Alcatels RNP A955 (radio network
  planning tool) for field strength prediction
  semi-empirical or ray-optical modelling
• Input for FSM algorithm Power plots of all cells
  covering the whole service area (multiple layers)
• Comparing predicted levels and those observed by
  the MS, the network can derive in which zone the
  MS is located

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Field Strength Mapping (FSM)RNP A955 for field
strength prediction
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Field Strength Mapping (FSM)Best Pattern
Matching 3D Illustration

• Search predicted pattern with mininum distance to
  observed level pattern (sum of squared
  distances).

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Description of Input Datafor Performance
Evaluation

• Input Data
• MS reference position GPS coordinates
• Standard GSM data Cell-ID, TA, measurement
  report (RXLEVs)
• BTS info coordinates of serving cell and
  neighbouring cells (CI), EIRPs, antenna azimuth,
  antenna pattern, ...
• For FSM method field strength prediction for
  each cell (RNP tool)
• Different geographical areas under test, e.g.
• Ruse (Bulgaria) suburban, 4.000 measurements
• Piotrkow (Poland) rural area, 3.800
  measurements
• Lodz (Poland) rural area, 4.400 measurements
• Alexandrow (Poland) suburban, 3.000
  measurements

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Input Data Lodz (Poland)MS reference positions

• rural area
• sectored cells only
• cell radius roughly10 km ... 15 km
• 1 measurement/s
• 4.400 measurements(1h)

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Accuracy of CITAExample Lodz
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Mean Accuracy of Positioning Algorithms
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Summary

• LCS is uncertain market
• many business opportunities next major revenue
  chance for telecomm operators
• services are slowly coming up and will evolve
  with customer usage
• Positioning techniques vary widely in terms of
  cost and accuracy
• robust CITANMR-based solution with full
  market penetration
• high variance of received power levels makes
  RXLEV-based positioning difficult, accuracy
  depends on cell size
• enhanced accuracy using GNSS technology (new
  handsets required)
• positioning accuracy vs. cost adapted to
  anticipated customer needs
• combination of various methods will provide best
  service availability and accuracy

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• Supplementary Slides

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Abbreviations
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Positioning technologies Assisted GNSS two
variants
Radio Measurements
Position calculation
X, Y

• Measurements are always done in the handset
• Position can be calculated...
• in the handset (MS-based) or
• in the SMLC (MS-assisted)
• User privacy is a major concern
• Position information property?
• Allows for indoors GPS due to sensitivity
  enhancements

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LCS network architecture3GPP Standard
LMU Type A
New elements
SRNC
HLR
Iub
Iups
3G SGSN
Uu
Iucs
Lg
Lh
3G MSC
Le
External
GMLC
SMLC
Lg
LCS client
Lg
SMLC
2G SGSN
MFS
Gb
Lg
Lb
-
BSC
2G MSC
A
TC
Ater
LMU Type A