towards mobile phone localization without war-driving

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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