Download - Cellular Positioning
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Cellular PositioningShashika Biyanwila
Research Engineer
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Cellular Positioning
Outline
• What is Cellular Positioning• Positioning Parameters• Feasible Approaches Identified• Implementation• Some Trial Results• Future Approach of the Research
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Cellular Positioning
What is cellular positioning ?
• Determining the position of a Mobile Station (MS), using location sensitive parameters
• Why ????– To provide Location Based Services…
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Cellular Positioning
Operator services
BillingNetwork management Location based services Wireless Gaming
Assistance
Roadside assistancePersonal or vehicle emergency Alarm managementDriving DirectionsTracking
Tracking criminalsTracking external resources containers etc
Monitoring
Monitoring delivery processFleet & freight trackingPersonal Child SecurityMobile Worker management
Information
TrafficNearest servicenewsnavigation helpadvertisingInformation Directory
Applications of cellular positioning
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Cellular Positioning
• 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)
Positioning Parameters
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Cellular Positioning
Feasible Approaches Identified
Positioning Techniques
1Geometrical
Approach
2Statistical Approach
3Database CorrelationApproach
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Cellular Positioning
1. Geometrical Approach
• Based on distance measurements
• Two Steps:
- Distance calculation
- Location Estimation
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Cellular Positioning
Geometrical approach contd..
• Distance Calculation - Measure the RSSI from neighboring cells - Apply Propagation models to calculate the distance
• Propagation Models- Hata Model- Extended Hata Model- Lee’s Model- CCIR Model- Walfisch-Ikegami Model (for micro cells)
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Cellular Positioning
2. Statistical Approach
• Construct a statistical propagation model for the RSSI- Find RSSI at distance d from the transmitter- Offsite calibration is necessary to estimate the
propagation parameters
• Define a probability distribution for the RSSI• Location estimation problem is solved as an inverse
or, rather, inference problem
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Cellular Positioning
Statistical Approach contd..
• Log-loss or Log-distance model • Gaussian Probability Distribution• Propagation Parameter Estimation
- Maximum Likelihood estimation• Location Estimation
- Maximum A posteriori Probability
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Cellular Positioning
Statistical Approach cntd..
• Area being considered is divided into several squares
• A posterior probability of the location be within a square, is calculated for each square
Square with Maximum A posterior
Probability
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Cellular Positioning
3. Database correlation Method (DCM)
• Involves a database of reference fingerprints for the whole area of interest.
• Fingerprint – a recorded measurement sample from a certain location in the area
GPS coordinates of a location
RSSI (from available cells) in that location
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Cellular Positioning
• How to collect fingerprints?• By measurements• Using a Network
planning tool
• High sampling resolution is needed.
Measurement
Fingerprint
Test route
Fingerprint
DCM contd…
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Cellular Positioning
• Location estimation
•Compare the input measurement with reference fingerprints
- Using Cost Functions•Location of the best matching reference fingerprint
Estimated Location
Input Measurement
DCM Algorithm
Database
Estimated Location
DCM contd…
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Cellular Positioning
Implementation
RSS
Measurement Unit
RSSI + GPS Reading
Commands•Interfacing Program•Database•Location Estimation Algorithm•Display Program
Software environment
Location ?
Hardware Environment
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Cellular Positioning
Trial & Results
• Urban
- Wellawaththa to Kolpetty
• Suburban
- Katubedda to Piliyandala
• Rural
- Ibbagamuwa
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Cellular Positioning
Urban area…..
CDF wise comparison for Urban area
0.00%
20.00%
40.00%
60.00%
80.00%
100.00%
120.00%
100 200 300 400 500 600 700 800 900 1000
Error Less Than (m)
Per
cent
age Geometrical
Statistical
DCM
Existing Method
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Cellular Positioning
Suburban area ……….
CDF wise comparison for Sub Urban area
0.00%
20.00%
40.00%
60.00%
80.00%
100.00%
120.00%
100 200 300 400 500 600 700 800 900 1000 1500 2000 2500
Error Less than (m)
Per
cent
age Geometrical
DCM
Existing Method
Statistical
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Cellular Positioning
Rural area ……..
CDF wise comparison for Rural area
0.00%
20.00%
40.00%
60.00%
80.00%
100.00%
120.00%
1000 1250 1500 1750 2000 2250 2500 2750 3000 3500 4000 4500 5000
Error Less Than (m)
Per
cent
age
Geometrical
DCM
Existing Method
Statistical
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Cellular Positioning
Future Approach of the Research
Improvements to the current DCM approach• Drawbacks
- Few instances of poor estimations
- Creating, updating & maintenance of the database
• How To Overcome
- Refined estimation techniques
- Use of a Network planning tool to create fingerprints
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Cellular Positioning
Implementation of a positioning engine and associated services
Services• Get your own location • Track others – web-based location on a map
GSM Network
Estimated Location
Received Signal
Fingerprint
Location Estimation using Received Signal Fingerprint & database
System
Information
Calibration
Fingerprints
Digital MapsPositioning Engine
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Thank You