1. Energy-Efficient Computing for Wildlife Tracking
Design Tradeoffs and Early Experiences with ZebraNet
Created by Chris Roedel
Presented by Israel Martinez

2. Some Graphics Courtesy of Princeton University ZebraNet Project
Overview
Background Information
Other Sensor Networks
ZebraNet Design Goals
Life as a Zebra
Collar Design
Protocol Design
Experimental Results
Discussion Questions
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

3. Background Information
Biology researchers want to track and monitor wild animals
Long term
Over long distances
Need detailed information about what the animals do to see how environment affects them
Current tracking techniques are far too primitive and are not very useful to researchers
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

4. Why Other Networks Won’t Suffice
No infrastructure to support Wired Networks => Wireless
Flying over an area and looking for VHF ‘ping’ signals
Can miss interesting events
Limited to daylight hours
Hard to obtain data from reclusive species
GPS + Satellite Uploads
Most sophisticated system can only store 3000 position entries & no biometric data
Satellite uploads are slow, power hungry and $$$$
Peer to Peer offers opportunity to improve
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

5. Some Graphics Courtesy of Princeton University ZebraNet Project
Contributions
First system to employ both mobile nodes AND mobile base stations
Specialized communication models that funnel data towards a base station and optimized for a high degree of latency tolerance
Examine energy tradeoffs using real system energy measurements from prototype in operation
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

6. Design Goals for ZebraNet
GPS Position taken every 3 minutes
Detailed activity logs for 3 minutes / hour
1 year ‘untouched’ operation
Operation over 100s or 1,000s of sq km
Latency is not critical, but high probability for delivering all data eventually
Zebra collar weight limit of 3-5 lbs.
No fixed base stations, antennas, or cell service
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

7. Some Graphics Courtesy of Princeton University ZebraNet Project
Day to Day as a Zebra
Social Structure
One type of Zebra moves in ‘Harems’
Generally, only one male in the ‘harem’ => reducing the number of collars need to track a large number of zebras
Groups of ‘Harems’ form Herds
These dynamics challenge ecologists, but will help ZebraNet transfer information between ‘harems’
Movement Patterns
Distance Moved
Net distance moved in a 3 minute period
One of three groups: Grazing, Graze-Walking, Fast Moving
Turning Angle
How far does the animal turn during each of the 3 phases
Water Sources and Drinking
Need to find water sources at least once per day
Sleep
Must rely on keeping watch and fleeing from predators
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

8. Some Graphics Courtesy of Princeton University ZebraNet Project
Zebra Movement Speeds
From Field Data
Grazing:
0.017m/s
Graze-walking:
0.072 m/s
Fast:
0.155 m/s
Turns ~ < 60°
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

9. Non-Intrusive Necklace Design
GPS, Flash RAM & CPU
Short Range Radio
Long Range Radio w/ Packet Modem
Does not show:
Packaging
Batteries
Solar Array
Power Management Circuits
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

10. Power and Weight Information
Idle
<1 mA
GPS Position Sampling & CPU / Storage
177 mA
Base Discovery only
432 mA
Transmit Data to Base
1622 mA
GPS chip + CPU
8 grams
Short-range Radio
20 grams
Long-range Radio and packet modem
296 grams
Rechargeable Batteries
287 grams
Solar Cell Array
540 grams
Total
1151 grams
Total Weight Goal 3-5 lbs.
Energy Goal: 5 days if no recharge
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

11. Basic Protocol in Action
Harem A
A,B
Harem A and Harem B come within short range radio range. They transfer their own information with each other
Harem B
B,A
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

12. Basic Protocol in Action
Harem A and Harem B move away from each other, but Harem B moves within range of Harem C, transferring both B’s and A’s information to C. Harem C transfers its information to B.
Harem C C
Harem A
A,B
Harem B
B,A
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

13. Basic Protocol in Action
Now Harem C is within Long Range Radio range of the mobile base station and can transfer its information along with B’s and A’s. The base station has the information from all the animals even though it only came within range of Harem C.
Harem C
C,B,A
Harem B
B,C,A
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

14. Some Graphics Courtesy of Princeton University ZebraNet Project
Protocol Design
Two peer-to-peer protocols evaluated here
Flooding: Send to everyone found in peer discovery.
History-Based: After peer discovery, choose at most one peer to send to per discovery period: the one with best past history of delivering data to base.
Compared to “direct”: no peer-to-peer, just to base
Success rate metric: Of all data produced in a month, what fraction was delivered to the base station?
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

15. Some Graphics Courtesy of Princeton University ZebraNet Project
ZNetSim
It’s a zebra mobility model and simulation environment for ZebraNet
It was armed with facts and field observation about zebra behavior and reasonable assumptions of the terrain and operating characteristics of the Mpala Research Center in Kenya
It returns two metrics:
Success rate – the percentage of data that gets back to the base station
Energy consumption
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

16. Some Graphics Courtesy of Princeton University ZebraNet Project
Experimental Results
Used their own ZNetSim simulator to vary parameters and determine best solution
These graphs show the difference between direct connections and peer-to-peer multihop
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

17. Experimental Results (cont)
Direct Connection proves to be the least reliable type of connection
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

18. Experimental Results (cont)
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

19. Experimental Results (cont)
Radio range key to data
homing success: ~3-4km for 50 collars in 20kmx20km area
Success rate:
Ideal: flooding best
Constrained bandwidth: history best
Energy trends make selective protocols best
Mobility model key to protocol evaluations
Fast random moves hurt history
Chicken and Egg:
mobility model is the biology research goal
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

20. Some Graphics Courtesy of Princeton University ZebraNet Project
Future Plans
Hardware:
Nov ‘02: waterproof prototype for local animal tests
Spring ’03: build final rugged version
Software:
Impala middleware:
Allow for wireless software updates & adaptivity
Beyond wildlife tracking:
Resource recovery, traffic management, security, surveillance…
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

21. Some Graphics Courtesy of Princeton University ZebraNet Project
Conclusions
ZebraNet as Engineering Research:
Early detailed look at mobile sensor net with mobile base stations
Demonstrates promise of large-extent, long-life sensor networks with GPS
Detailed look at power/energy concerns
ZebraNet as Biology Research:
Enabling technology for long-range migration research
Good view of key inter-species interactions
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project

22. Some Graphics Courtesy of Princeton University ZebraNet Project
Discussion Questions?
Does this model what they want?
What other animals could be fitted with these sensors?
12/4/2018
Some Graphics Courtesy of Princeton University ZebraNet Project