Wireless Sensor Networksfor Habitat Monitoring

Alan Mainwaring1

Joseph Polastre2

Robert Szewczyk2

David Culler1,2

John Anderson3

1: Intel Research Laboratory at Berkeley

2: University of California, Berkeley

3: College of the Atlantic

Introduction

• Application Driven System Design, Research, and Implementation

• Parameterizes Systems Research:– Localization– Calibration– Routing and Low-Power Communications– Data Consistency, Storage, and Replication

• How Can All of these Services and Systems Be Integrated into a Complete Application?

Great Duck Island

• Breeding area for Leach’s Storm Petrel (pelagic seabird)

• Ecological models may use multiple parameters such as:– Burrow (nest) occupancy during

incubation– Differences in the micro-climates

of active vs. inactive burrows – Environmental conditions during

7 month breeding season

Application

> 1000 ft

Sensor Network Solution

Outline

• Application Requirements• Habitat Monitoring Architecture

– Sensor Node– Power Management– Sensor Patch– Transit Network– Wide Area Network and Disconnected Operation

• Sensor Data• System Analysis• Real World Challenges

Application Requirements

• Sensor Network– Longevity: 7-9 months– Space: Must fit inside Small Burrow– Quantity: Approximately 50 per patch– Environmental Conditions– Varying Geographic Distances

• Inconspicuous Operation– Reduce the “observer effect”

• Data– As Much as Possible in the Power Budget– Iterative Process

Application Requirements

• Predictable System Behavior– Reliable– Meaningful Sensor Readings

• Multiple Levels of Connectivity– Management at a Distance– Intermittent Connectivity– Operating Off the Grid– Hierarchy of Networks / Data Archiving

Habitat Monitoring Architecture

Transit Network

Basestation

Gateway

Sensor Patch

Patch Network

Base-Remote Link

Data Service

Internet

Client Data Browsingand Processing

Sensor Node

Sensor Node: Mica

• Hardware– Atmel AVR w/ 512kB Flash– 916MHz 40kbps Radio

• Range: max 100 ft• Affected by obstacles, RF propogation

– 2 AA Batteries• Operating: 15mA• Sleep: 50A

• Software – TinyOS / C Applications– Power Management– Digital Sensor Drivers– Remote Management & Diagnositcs

Sensor Node: Power Management

• AA Batteries have ~2500 mAh capacity• Mica consumes 50A in sleep = 1.2 mAh/day

Node Activity Days Years

Mica Always On 7 0.1

Mica Always Sleeping 2081 5.7

Number of Operating Hours per Day

Exp

ecte

d Li

fetim

e (d

ays

)

Mica Expected Lifetime

Sensor Node: Power Management

• Target Lifetime: 7-8 months• Power Budget: 6.9mAh/day• Questions:

– What can be done?– How often?– What is the resulting sample

rate?

Operation nAh

Transmitting a packet 20.000

Receiving a packet 8.000

Radio Listening for 1ms 1.250

Operating Sensor for 1s (analog) 1.080

Operating Sensor for 1s (digital) 0.347

Reading a Sample from the ADC 0.011

Flash Read Data 1.111

Flash Program/Erase Data 83.333

Operation Operating Time per Day Duty Cycle Sample Rate

Always Sleep 24 hours 0% 0 samples/day

+ CPU on 52 minutes 3.61% 0 samples/day

+ Radio On (Listen) 28 minutes 1.94% 0 samples/day

+ Sample All Sensors 21 minutes 1.45% 630 samples/day

+ Transmit Samples 20 minutes 1.38% 600 samples/day

Sensor Node: Mica Weather Board

• Digital Sensor Interface to Mica– Onboard ADC

• Designed for Low Power Operation– Individual digital switch

for each sensor

• Designed to Coexist with Other Sensor Boards– Hardware “Enable”

Protocol to obtain exclusive access to connector resources

Sensor Node: Mica Weather Board

Sensor Accuracy Interchange Max Rate Startup Current

Photo N/A 10% 2000 Hz 10 ms 1.235 mA

I2C Temp 1 K 0.2 K 2 Hz 500 ms 0.150 mA

Pressure 1.5 mbar 0.5% 10 Hz 500 ms 0.010 mA

Press Temp 0.8 K 0.24 K 10 Hz 500 ms 0.010 mA

Humidity 2% 3% 500 Hz 500 ms 0.775 mA

Thermopile 3 K 5% 2000 Hz 200 ms 0.170 mA

Thermistor 5 K 10% 2000 Hz 10 ms 0.126 mA

Important to Biologists Affect Power Budget

Sensor Node: Packaging

• Parylene Sealant

• Acrylic Enclosures

Sensor Patch Network• Transmit Only Network• Single Hop• Repeaters

– 2 hop initially– Most Energy Challenged

• Adheres toPower Budget

• Nodes:– Approximately 50

– Half in burrows, Half outside

– RF unpredictable• Burrows

• Obstacles

• Drop packets or retry?

Transit Network

• Two implementations– Linux (CerfCube)– Relay Mote

• Antennae– No gain antenna (small)– Omnidirectional– Yagi (Directional)

• Implementation of transit network depends on:– Distance– Obstacles– Power Budget

• Duty cycle of sensor nodes dictates transit network duty cycle

Transit Network

• Renewable Energy Sources

– CerfCube needs 60Wh/day– Assuming an average

peak of 1 direct sunlight hour per day:

– Panel must be 924 in2

or 30” x 30” for a 5” x 5” device!

– A mote only needs 2Wh per day, or a panel 6” x 6”

SizeW/in065.0

1

Hoursr Peak Winte

Dayper Hours WattsTotal2

Base Station / Wide Area Network

• Disconnected Operation and Multiple Levels of State– Laptop

• DirecWay Satellite WAN• PostgreSQL• 47% uptime

– Redundancy and Replication• Increase number of points of failure

– Remote Access• Physical Access Limited

– Keep state all areas of network

– Resiliency to• Disconnection• Network Failures• Packet Loss

– Potential Solution:Keep Local CachesSynchronization

Sensor Data Analysis

Sensor Data Analysis

Outside Burrow Inside Burrow

System Analysis

• Power Management Goals– Calculated 7 months, expect

4 months– Battery half-life at 1.2V

• Predictable Operation– Observed per node constant

throughput, % loss– 739,846 samples as of 9/23,

network is still runningBattery Consumption at Node 57 Packet Throughput and Active Nodes

Real World Experiences• System and Sensor Network Challenges

– Low Power Operation (low duty cycle)• Affects hardware and software implementation

– Multihop Routing • Allows bigger patches• Route around physical obstacles• Must have ~1% operating duty cycle

– In Situ Retasking/Reconfiguration• Let biologists interactively change data collection patterns• Not Implemented due to conservative energy implementation

– Lack of Physical Access• Remote management• Disconnected operation• Fault tolerance• Reliance on other people and their networks

– Physical Size of Device• Affects microcontroller selection, radio, practical choice of power

sources

Real World Experiences• Failures

– Extended Loss of Wide Area Connectivity– Unreliable Reboot Sequence in Windows– Solderless Connections Fail

(expansion/contraction cycles)– Node Attrition (Petrels are not mote neutral)– Environmental Conditions (50km/hr gale

winds knock over equipment)– Lack of post-mortem diagnositics

Conclusions

• First long term outdoor wireless sensor network application

• Application driven sensor network design– Defines requirements and constraints on core

system components (routing, retasking, fault tolerance, power management)

Backup Slides

Mote 18: Outside

Mote 26: Burrow 115a

Mote 53: Burrow 115b

Mote 47: Burrow 88a

Mote 40: Burrow 88b

Mote 39: Burrow 84