Cellular Positioning Shashika Biyanwila Research Engineer
Dec 18, 2015
Cellular Positioning
Outline
• What is Cellular Positioning• Positioning Parameters• Feasible Approaches Identified• Implementation• Some Trial Results• Future Approach of the Research
Cellular Positioning
What is cellular positioning ?
• Determining the position of a Mobile Station (MS), using location sensitive parameters
• Why ????– To provide Location Based Services…
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
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
Cellular Positioning
Feasible Approaches Identified
Positioning Techniques
1Geometrical
Approach
2Statistical Approach
3Database CorrelationApproach
Cellular Positioning
1. Geometrical Approach
• Based on distance measurements
• Two Steps:
- Distance calculation
- Location Estimation
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)
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
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
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
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
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…
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…
Cellular Positioning
Implementation
RSS
Measurement Unit
RSSI + GPS Reading
Commands•Interfacing Program•Database•Location Estimation Algorithm•Display Program
Software environment
Location ?
Hardware Environment
Cellular Positioning
Trial & Results
• Urban
- Wellawaththa to Kolpetty
• Suburban
- Katubedda to Piliyandala
• Rural
- Ibbagamuwa
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
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
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
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
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