U.S. Patent #8,036,679 – Optimizing Performance of Location-Aware Applications Using State Machinesbarbeau@cutr.usf.edu

(813) 974-7208locationaware.usf.edu

Sean J. Barbeau, Philip L. Winters, Rafael A. Perez, Miguel A. Labrador, Nevine L. Georggi

Center for Urban Transportation Research and Department of Computer Science & Engineering

Introduction

GPS Auto-SleepOptimizing performance of location-aware mobile apps

GPS-enabled mobile phones provide many new opportunities for high-resolution Location-based Services (LBS) via mobile apps

a) Old low-res tracking b) New high-res tracking

Problem

Frequent use of GPS severely affects battery life of mobile devices

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network

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network

4 sec. sampling interval0

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9Negative Impact of GPS on Battery Life

Sanyo Pro 200

HTC Hero (Android 2.1)Ba

tter

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29.7 meters

4 second GPS sampling

5 minute GPS sampling

Challenge

Moving

Stoppe

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Prototype Testing with Mobile Devices Conclusion

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Interval Between GPS Fixes (s)

Batt

ery

Life

(hou

rs)

Varying GPS Interval Saves En-ergy

Sprint-Nextel for providing mobile devices and cellular service for this research

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Inte

rval

Bet

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What if we could dynamically change the GPS sampling interval on the phone? Would this save battery life while providing high-res tracking?

Problem: GPS error makes detecting stops and starts difficult. Error frequently triggers false GPS on/offs

What if we treat the problem as continuum instead of binary state?

State0

State1

Staten – 1

Staten

Move directly to state[0] when speed exceeds high_speed threshold

Location Recalculation

Interval = 4 sec.

Location Recalculation

Interval = 8 sec.

Location Recalculation

Interval = 64 sec.

Location Recalculation

Interval = 128 sec.

Move gradually towards state[n] when (speed < low_speed value) and (distance_between_fixes < distance_threshold).

Move gradually towards state[0] when (speed < high_speed value) and (distance_between_fixes > distance_threshold).

Innovation

We implement this concept as a state machine in mobile app code. Will this limit the impact of GPS outliers on GPS sampling interval changes and increase battery life?

“Awake” to “Asleep” Transitions

“Asleep”

“Awake”

Min Max Mean 95th30.00%40.00%50.00%60.00%70.00%80.00%90.00%

100.00%State Accuracy

GPS Auto-Sleep correctly tracks states (mean accuracy of 88.4%), and extends mobile device battery life from 8 to 16 or more hours.

Energy Benefits