GPS AUTO-SLEEP FOR ENERGY-EFFICIENT LOCATION

TRACKINGSean Barbeau, Phil Winters, Nevine Georggi

Center for Urban Transportation Research

Rafael Perez, Miguel LabradorDepartment of Computer Science & Engineering

Portions of work funded by the Florida Department of Transportation and the National Center for Transit Research

Protected under US Patent # 8,036,679

PROBLEM

• Past vehicle-based GPS tracking give low-resolution view of daily travel behavior

• Are these GPS fixes:– Points-of-interest?– Stops in traffic?

• Difficult to extract info:– Distance traveled– Origin-Destination pairs

• Misses non-vehicle trips2

Protected under US Patent # 8,036,679

INNOVATION

• Our research team created TRAC-IT, a GPS-enabled mobile phone app

• TRAC-IT can capture “high-definition” view of travel behavior

• Much easier to determine:– Path, distance traveled– Origin-Destination pairs– Avg. speeds

• Can capture transit/bike/walk trips

3Protected under US Patent # 8,036,679

NEW PROBLEM

• We can record GPS fixes as frequently as once per second and send to our server

• However, frequent GPS fixes come at great cost to:– battery energy– data transfer over network

• Both battery life and cell network data transfer are very limited resources

4Protected under US Patent # 8,036,679

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4 sec. sampling interval

Batt

ery

Life

(hou

rs)

Impact of GPS on Battery Life

Sanyo Pro 200

HTC Hero (Android 2.1)

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Sprint CDMA EV-DO Rev. A

network

Sprint CDMA EV-DO Rev. A

network

One-day Requirement

Protected under US Patent # 8,036,679

NEW IDEA

• What if we could dynamically change the GPS sampling interval on the phone?– Use four second sampling interval

when moving– Use five minute interval when

stopped• Challenges:

– Can we create mobile apps that do this?

– Would this be enough to make a difference in battery life?

– How do we handle GPS noise when trying to detect movement?

6Protected under US Patent # 8,036,679

GPS DATA NOISE CAUSES UNCERTAINTY IN MOVEMENT

729.7 meters

HTC HeroSprint EV-DO Rev A network

Protected under US Patent # 8,036,679

DETECTING USER MOVEMENT

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• GPS noise causes uncertainty in states• Many false transitions waste battery energy

4 second GPS sampling 5 minute GPS sampling

Protected under US Patent # 8,036,679

DETECTING USER MOVEMENT

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4 second GPS sampling 5 minute GPS sampling

• What if we represent this binary, or two-state, problem more like a continuum?

Protected under US Patent # 8,036,679

1010

• Gradually change GPS interval from “awake” to “asleep” based on certainty in user’s movement• With some data (e.g., very high speeds) snap back to “awake”

“ASLEEP”“AWAKE”

State0

State1

Staten – 1

Staten

Move towards state[0] upon successful condition evaluation, or jump to state[0]

Move towards state[n] upon failed condition evaluation

GPS Interval =4 sec.

GPS Interval =8 sec.

GPS Interval =2 min.

GPS Interval =5 min.

New invention – GPS Auto-Sleep

Protected under US Patent # 8,036,679

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Sanyo Pro 200

Sprint CDMA EV-DO Rev. A

network

Protected under US Patent # 8,036,679

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Sanyo Pro 200

Sprint CDMA EV-DO Rev. A

network

“Asleep”

“Awake”

Protected under US Patent # 8,036,679

13n = 30

Evaluation – Summary of 30 tests

Protected under US Patent # 8,036,679

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Batt

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Life

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TRAC-IT TRAC-IT with GPS Auto-Sleep

EVALUATION – DAILY TRACKING

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Sanyo Pro 200Sprint CDMA EV-DO Rev. A

network

Impact of GPS Auto-Sleep on Battery Life

Protected under US Patent # 8,036,679

POTENTIAL DATA SAVINGS – GPS AUTO-SLEEP

With GPS Auto-

Sleep

WithoutGPS Auto-Sleep

# Assisted GPS Fixes Over 13 hrs

1,035(~0.1 MB)

11,700(~1.4 MB)

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• Assuming each GPS fix is transmitted to server, GPS Auto-Sleep saves ~1.3MB in data transfer PER PHONE in 13 hours

*Sleep time of 120 seconds between GPS fixes while user is not moving, and 4 seconds between GPS fixes while user is moving

Protected under US Patent # 8,036,679

PATENT ISSUED ON OCT. 11, 2011

US Patent # 8,036,679 Optimizing Performance of Location-Aware Applications using State Machines

16Protected under US Patent # 8,036,679

UTILITY & COMMERCIALIZATION

• We have been tracking high-def travel behavior of over 30 participants over 9 months– Using TRAC-IT mobile app w/ GPS Auto-Sleep– USDOT-funded Value Pricing project

• DAJUTA, a Florida-based company, has non-exclusively licensed the technology from USF– Other companies are also expressing interest

• GPS Auto-Sleep is one module in “Location-Aware Information Systems Client (LAISYC)” framework– 15 patents pending on other modules

17Protected under US Patent # 8,036,679

THANK YOU

Questions?

Sean Barbeau, M.S.Research Associatebarbeau@cutr.usf.edu(813) 974-7208 locationaware.usf.edu

18Protected under US Patent # 8,036,679