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On the Effectiveness of Energy Metering on Every Node
Qiang Li Omprakash Gnawali University of Houston Marcelo Martins Rodrigo Fonseca Brown University May 22, 2013 IEEE DCOSS
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Energy Accounting in Sensor Networks
Many projects optimize energy Power information necessary Ways to understand power draw of a system Direct measurement: accurate but costly Estimate: use a model, maybe not as accurate
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If you can measure power, just measure it.
If you can’t measure, need to model and estimate.
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If you can’t measure, need to model and estimate
Some platforms and large networks hard to measure
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Energy Accounting in Practice
Individual mote Direct measurement (iCount, Nemo) Counter-based models: Event counts, IO FSM models: 2-State FSM, System Call Driven FSM Network-wide estimation Direct measurement (Quanto Testbed) Network-wide models Proxies: Activity Accounting (e.g., num TX)
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Questions Do we need to measure power on all the nodes?
Power models Simple workloads Real-world complex workloads Do we need to adapt power models over time?
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Questions Do we need to measure power on all the nodes?
Power models Simple workloads Real-world complex workloads Do we need to adapt power models over time?
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Power Model A relationship between activity and power draw
Measurement Model Example: radio on (30mA), radio off (5mA)
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Creating Power Model Power = A * DUTY_CYCLE + BASE_POWER
Linear regression to calibrate A and BASE_POWER
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Global Model Build a power model
Measurement Model Build a power model Make one mote do a task Measure power Use the power model to estimate power for rest of the nodes for that task
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Individual Model Build a per-node power model
Measurement Model Build a per-node power model Make a mote do a task Measure power User the model to estimate power rest of the time for that node Node1 Measurement Model Node2
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Do We Need Individual Model?
Measurement Model Measurement Model Node1 Node3 Measurement Model Measurement Model Node4 Node2
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Questions Do we need to measure power on all the nodes?
Power models Simple workloads Real-world complex workloads Do we need to adapt power models over time?
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Testbed 240 Quanto Testbed Motes Epic motes [IPSN 08]
iCount onboard measurement [IPSN 08]
![Testbed 240 Quanto Testbed Motes Epic motes [IPSN 08]](http://slideplayer.com./slide/12863385/78/images/14/Testbed+240+Quanto+Testbed+Motes+Epic+motes+%5BIPSN+08%5D.jpg "iCount onboard measurement [IPSN 08]")
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Simple Workload Experiment
Idle CPU Radio Calibration Program Program Program Program Time-Synchronized execution of identical workloads on all the nodes in a loop
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Current Draw Variation Across Motes
Measurements with Identical Workloads Current Draw of 96 motes across Temperature Current Draw across 240 motes Current Draw Distribution Variation up to 15% and resembles Normal Distribution
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What if we build model from measurement of subset of nodes?
N measurements What if we build model from measurement of subset of nodes?
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Building Model From Subset of Nodes
Estimating Avg energy use Estimating Max energy use 90% For Max energy estimation, worst-case error 10% with model based on measurements on 90% nodes.
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Questions Do we need to measure power on all the nodes?
Power models Simple workloads Real-world complex workloads Do we need to adapt power models over time?
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Creating Different Workload Across Motes
CTP workload Experiment 100 motes Channel 26 1-s LPL sleep interval
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Creating Power Model Power = A * DUTY_CYCLE + BASE_POWER
Use linear regression to calibrate A and BASE_POWER
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CTP: Building Model with a Subset
Calibrated by one mote Calibrated by a subset Accuracy > 97% by measuring 10% motes
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Questions Do we need to measure power on all the nodes?
Power models Simple workloads Real-world complex workloads Do we need to adapt power models over time?
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Models That Change Over Time
Factors that may change power draw Temperature Humidity Adapting models Temperature Global temperature-power model Individual temperature-power model
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Quanto: Temperature And Current
Change due to temperature < 1.6%
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TelosB: Temperature and Current
Measure current at -14℃ to 45℃ on 6 motes Change in Current Workloads Small change in current even with large change in temperature
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Questions Do we need to measure power on all the nodes?
Power models Simple workloads Real-world complex workloads Do we need to adapt power models over time?
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Adapting Models to Temperature
Worst-case error Relative Error (percent) Avg error Global Individual Individual Individual + Global Temp + Individual Temp Limited gain from incorporating temperature in the model
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Conclusion Variation in energy across nodes significant (careful when using energy proxies) Power model based on subset reduces errors Impact of Temperature on power limited Omprakash Gnawali
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