Towards Runtime Support for Energy Awareness in Wireless Sensor Networks

Institut for Technical Informatics

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Thomas Trathnigg Towards Runtime Support for Energy Awareness in WSNs

Towards Runtime Support for Energy Awareness in Wireless Sensor Networks

Thomas Trathnigg and Reinhold WeissInstitute for Technical Informatics

Graz University of TechnologyGraz, A-8010 Austria

{trathnigg,rweiss}@iti.tugraz.at


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Outline

• Introduction• Measuring Energy in WSNs• Measurement Setup• Error Analysis• Validate PowerTOSSIM• Conclusion + Outlook


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Introduction

Lifetime of a wireless sensor network depends on the energy consumption of each node

Limited energy-budget– Battery-powered

– Energy harvesting

Energy-awareness– Energy-aware routing

– Dynamic Power Management

– …


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Introduction

Monitor the energy consumption of each mote

Online monitoring

Simulator calibration

Requirements– accurate

– low-power

– small

– inexpensive


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Mica2 Motes

ATMEGA 128L – 7.3 Mhz 8-bit CPU– 128 KB code, 4 KB RAM

433, 868 or 916 Mhz, 76.8 Kbps FSK radio transceiver

512 KB flash for logging

Sandwich-on sensor boards

Powered by 2 AA batteries


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Typical Current Profile of Mica2

14-bit 100MHz dual-channel Digitizer (National Instruments)

Fast changes in current profile due to cpu and radio state changes

Clamp-on current probes

„Fuel Gauges“– Based on peridodical ADC sampling

Energy-Driven Sampling – Based on an approach published by

Chang et al. – Detecting software hotspots on a

PDA


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Measurement Setup


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Error Analysis

• Non-ideal behavior of electrical components– discharge time of capacitor

• 500ns, 1000:1 ratio at 35mA; 0.1% error

• Voltage at the mote– voltage drop caused by shunt resistor

• <2% error

• Current-sense amplifier– error is below 2% in the range 3 to 66mA

• Bandwith of current-sense amplifier– fastest current change measured on mica2 mote 2.4mV/s

We expect the error of our setup to be below 5%


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Calibration + Verfication

Determined the amount of energy a ramp depicts (54J)

Verification– Stable voltage supply 3V

– Constant current load

– 60s measurments

– Comparision of measurement with calculated result

Supply

Ramp

UCUE


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Error of Measurement Setup


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Validate PowerTOSSIM

TinyOS 1.1.15

PowerTOSSIM– Support only for mica2

– used CPU cycle counting

mica2 (868MHz)– Deluge disabled

Several TinyOS Applications measured for 60s


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Typical TinyOS Applications


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Analysis of PowerTOSSIM Divergence

Possible reasons– Measurement errors– Inaccuracies in the simulation

PowerTOSSIM simulates at 4MHz, mica2 motes operate at 7.38MHz

– Power-model of PowerTOSSIMsystematic errors

values of the power-model may be inaccurate443MHz vs 868MHz

Other hardware differences


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Energy Consumption of Different Motes

No mica2 motes at 443MHz available, so we checked only other hardware differences

8 different mica2 motes

4% max. difference for Blink

3.4% max. difference for CntToRfm


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Conclusion + Outlook

Approach of energy-based sampling is feasible– size– cost– low-power, should be improved– accuracy

• range must be increased

Improve/calibrate energy model of PowerTOSSIM

Redesign of measurement setup– measurement range– low-power– integration on mica2 sensorboard

Towards Runtime Support for Energy Awareness in Wireless Sensor Networks

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