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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)
5
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
8
• 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
9
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
11
Sanyo Pro 200
Sprint CDMA EV-DO Rev. A
network
Protected under US Patent # 8,036,679
12
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
ery
Life
(hou
rs)
TRAC-IT TRAC-IT with GPS Auto-Sleep
EVALUATION – DAILY TRACKING
14
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)
15
• 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
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