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Towards Mobile Phone Localization without War-Driving. Location is an IP address. for content delivery. Is GPS the solution? Pros: Good accuracy Cons: Poor battery lifetime Is GSM the solution? - PowerPoint PPT Presentation
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Towards Mobile Phone Localization without War-Driving
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Location is an IP addressLocation is an IP addressfor content delivery
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Is GPS the solution?
Pros: Good accuracy Cons: Poor battery lifetime
Is GSM the solution?
Pros: Long battery lifetime Cons: Poor accuracy
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What about WiFi Localization?
E.g., SkyHook:
Basic Idea:1. Several trucks war-drive a place2. Create Radio map = <Location: WiFi IDs>3. Distribute map to phones4. Phone user goes to war-driven region, overhears WiFi
IDs5. Reverse Look Up IDs against radio map6. Obtains location
Basic Idea:1. Several trucks war-drive a place2. Create Radio map = <Location: WiFi IDs>3. Distribute map to phones4. Phone user goes to war-driven region, overhears WiFi
IDs5. Reverse Look Up IDs against radio map6. Obtains location
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Is Skyhook the solution?
Middle GroundLower Accuracy than GPS, Longer Battery lifetime Better Accuracy than GSM, Shorter Battery lifetime
but …
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Is Skyhook the solution?
Middle GroundLower Accuracy than GPS, Longer Battery lifetime Better Accuracy than GSM, Shorter Battery lifetime
but …
At the cost of: Degraded location accuracy: walking paths ~ 60m Reliance on infrastructure (APs) War-driving ($$ + carbon footprint)
“NYTimes: Skyhook fleet 500 trucks/drivers”
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Visual RepresentationOf the
State of the Art
(Duke Campus)
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GPS unusable with phone batteryGSM too inaccurate
SkyHook
No Eng. Eff. & Acc. Solution
SkyhookBetter than GPS Eng. Eff.
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GPS unusable with phone battery
CompAcc
Eng. Eff. & Acc. Solution
GPS unusable with phone batteryGSM too inaccurate
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Contents
CompAcc
Evaluation
Limitations and Future Work
Conclusion
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Contents
CompAcc
Evaluation
Limitations and Future Work
Conclusion
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Goals
No War-Driving Cannot drive walking paths (campus, parks, …) Expensive / Environment unfriendly
No reliance on WiFi infrastructure Rural regions / developing countries
Good accuracy (~GPS)
Improve energy-efficiency Better than Skyhook, GPS
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CompAcc: Basic Idea
Direction(compass) + Displacement(accelerometer) = User’s directional trail
Directional Trail
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CompAcc: Basic Idea
Direction(compass) + Displacement(accelerometer) = User’s directional trail
Compute path signatures Derived from a local electronic map (Google Maps)
Path Signature …
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CompAcc: Basic Idea
Direction(compass) + Displacement(accelerometer) = User’s directional trail
Compute path signatures Derived from a local electronic map (Google Maps)
Compare directional trail with path signatures Best match provides the user location
Directional Trail
Path Signature …
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Path Signature … Directional Trail
Correct location errors at turns
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Path Signature … Directional Trail
Correct location errors at turns
Directional Trail
Path Signature …
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Advantages
No war-driving No reliance on WiFi infrastructure
Maps available ubiquitously
Improves battery lifetime GPS ~10h Skyhook ~16h Accelerometer ~ 39h Compass ~48h
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Architecture
Tile Database
Tile Database
6. Current location(lat A, long B)
2. Report initial location(lat X, long Y)
Tile
4. Direction(Compass)
5. Displacement(Accelerometer)
1. Initial location GPS:(lat X, long Y)
CompAcc
Initial location Directional trail Current location
3. Obtain paths in the user vicinity
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Directional trail: displacement
Accelerometer based step count displacement = step_count * step_size
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Directional trail: direction
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Directional trail: direction
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Path Signature
Extract from Google Maps Geodesic formulas
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Matching Directional Trail with Path Signatures
Dissimilarity Metric:
ci = compass readingspi = path computed directionN = directional trail size
Directional Trail
Path Signature
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Contents
CompAcc
Evaluation
Limitations and Future Work
Conclusion
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Results
Compared 3 localization schemes CompAcc Skyhook Wifi-War-Walk (We war-droved walking paths in campus)
Metrics Instantaneous Error = distance(estimated, real) Average Localization Error (ALE) = Average Instantaneous
Error
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CompAcc Instantaneous Error
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CompAcc Instantaneous Error
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Results
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Results
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Results
Average ALEGPS: 10m
CompAcc: 11mWiFi-War-Walk: 30m
Skyhook: 70m
Energy GPS: 10h
CompAcc: 23hWiFi-War-Walk:16h
Skyhook:16h
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Skyhook CompAcc
g – GPS s – Skyhook c - CompAcc Assume GPS is absolute
truth
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Contents
CompAcc
Evaluation
Limitations and Future Work
Conclusion
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Limitations and Future Work
Map Generation Manually mark footpaths
User Position Estimated along the Path Apply particle filters to accommodate wide roads
Multiplexing between Localization Methods Hand-off to Skyhook/GPS when driving Extend to vehicular movement
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Contents
CompAcc
Evaluation
Limitations and Future Work
Conclusion
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CompAcc
Today’s localization technologies limited Energy- Efficiency Coverage/Accuracy
Rely on simple localization mechanism Need: Compass, Accelerometer and Maps
Evaluation results: ALE: 11m Battery: 23h
CompAcc scales to any mapped part of the world
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Questions?
Thank You!
Visit the SyNRG research group @http://synrg.ee.duke.edu/
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Additional Slides
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Skyhook on walking paths
g – GPS positionS – Skyhook position
Assume GPS is absolute truth
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Skyhook Coverage
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Directional trail: displacement
Step count/displacement accuracy
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Trail/Path Size
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Fallback Mechanism: A-GPS
What if the dissimilarity metric is large? Trigger A-GPS
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Fallback Mechanism
Estimated Location
7th Street
5th Street
Main
St.
AA
EE
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Fallback Mechanism
Estimated Location
7th Street
5th Street
Main
St.
AA
EE
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Context
Pervasive wireless connectivity+
Localization technology=
Location-based applications (LBAs) Location-based applications (LBAs)
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Context
Pervasive wireless connectivity+
Localization technology=
(iPhone AppStore: 3000 LBAs, Android: 600
LBAs)
Location-based applications (LBAs) Location-based applications (LBAs)
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Location-Based Applications (LBAs)
Examples:
Location-based recommendations, geo-tagging GeoLife: shopping list when near a grocery storeTrafficSense: real-time traffic conditions
Location expresses context of user Facilitates content delivery
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Localization Technology
LBAs executed on mobile phones
Accuracy Technology Energy-
Efficiency 10m GPS 4h-8h 20-40m WiFi / Skyhook 16h 200-400m GSM ~days
Accuracy Technology Energy-
Efficiency 10m GPS 4h-8h 20-40m WiFi / Skyhook 16h 200-400m GSM ~days
