Description of a software technique and real-world benchmarks for mobile application developers that can significantly reduce the impact of the use of GPS on a mobile device's battery life.

1. GPS AUTO-SLEEP
FOR ENERGY-EFFICIENT LOCATION
TRACKING
Sean Barbeau, Phil Winters, Nevine Georggi
Center for Urban Transportation Research
Rafael Perez, Miguel Labrador
Department 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

2. 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 trips
2
Protected under US Patent # 8,036,679

3. 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
3
Protected under US Patent # 8,036,679

4. 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
4
Protected under US Patent # 8,036,679

5. 0
1
2
3
4
5
6
7
8
9
4 sec. sampling interval
BatteryLife(hours)
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

6. 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?
6
Protected under US Patent # 8,036,679

7. GPS DATA NOISE CAUSES UNCERTAINTY IN
MOVEMENT
7
29.7 meters
HTC Hero
Sprint EV-DO Rev A network
Protected under US Patent # 8,036,679

8. 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

9. 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

10. 10
10
• 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”
New invention – GPS Auto-Sleep
Protected under US Patent # 8,036,679

11. 11
Sanyo
Pro 200
Sprint CDMA
EV-DO Rev. A
network
Protected under US Patent # 8,036,679

12. 12
Sanyo Pro 200
Sprint CDMA
EV-DO Rev. A
network
“Asleep”
“Awake”
Protected under US Patent # 8,036,679

13. 13
n = 30
Evaluation – Summary of 30 tests
Protected under US Patent # 8,036,679

14. 0
2
4
6
8
10
12
14
16
18
BatteryLife(hours)
TRAC-IT TRAC-IT with GPS Auto-Sleep
EVALUATION – DAILY TRACKING
14
Sanyo Pro 200
Sprint CDMA
EV-DO Rev. A
network
Impact of GPS Auto-Sleep on Battery Life
Protected under US Patent # 8,036,679

15. POTENTIAL DATA SAVINGS – GPS AUTO-SLEEP
With
GPS Auto-
Sleep
Without
GPS 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

16. PATENT ISSUED ON OCT. 11, 2011
US Patent # 8,036,679
Optimizing Performance of Location-Aware Applications using State M
16
Protected under US Patent # 8,036,679

17. 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 17
Protected under US Patent # 8,036,679

18. THANK YOU
Questions?
Sean Barbeau, M.S.
Research Associate
barbeau@cutr.usf.edu
(813) 974-7208
locationaware.usf.edu
18
Protected under US Patent # 8,036,679