Protocol assessment issues in low duty cycle sensor networks: The switching energy

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Protocol assessment issues in low duty cycle
sensor networks The switching energy

• A.G. Ruzzelli, P. Cotan, G.M.P. OHare, R.
  Tynan, and P.J.M Havinga

Adaptive Information Cluster (AIC) group _at_ PRISM
Laboratory School of Computer Science and
Informatics, University College Dublin (UCD),
Ireland. Department of Electronic Engineering,
Technical University of Catalonia,
Spain. Department of Computer Science,
University of Twente, The Netherlands.
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Summary

• Generality on protocol energy assessment
• The low duty Cycle through the wake up concept
• Switching between transceiver states
• Phase1 Board measurements
• The sensor node
• The experimental approach
• The measured results
• Phase2 Switching energy assessment
• The S-MAC protocol
• Performance evaluation
• Simulation setup
• Simulated results
• Considerations
• Conclusions

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Generality on protocol energy assessment

• Energy consumption mainly due to the transceiver
  activity
• Protocol energy assessment based on transceiver
  states
• Transmit time
• Receive time
• Idle time (Sleeping time in sensor-nets)
• Switching time (USUALLY NOT ASSESSED)
• Switching energy negligible in ad-hoc wireless
  network protocol assessment (e.g. WiFi)

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Switching in standard wireless networks

• Is defined as the transition time that elapses
  between the end of a transceiver state and the
  beginning of the following one
• Possible switching states consist of
• RX/TX and TX/RX
• TX/Sleep and Sleep/TX
• RX/Sleep and Sleep/RX
• State transition is fast ? little amount of
  energy is consumed.
• Switching energy is much smaller than total
  energy spent.
• Transceiver data sheets report average switching
  time but not the energy spent.
• Related work show that assessment of novel
  protocol architectures for WSNs inherited the
  switching energy negligibility.

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Sensor network characteristics

• Energy consumption primary objective
• The wake-up concept
• Very low duty cycle (even less than 5)
• Small packets smaller than in ad-hoc networks
  (e.g. temperature data is few bytes)
• Low data traffic per node

Can we consider switching energy still negligible
for low duty cycle sensor networks?
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Phase 1 The experimental model

• Analysis conducted on different EYES sensor node
  prototypes
• Prototypes mounted different off-the shelf
  transceiver for sensor networks
• Investigation of Tr1001, CC1000 and CC1010
  transceivers

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Phase 1The experimental approach

• The voltage drop is gauged across high-side
  series resistor placed between the battery (
  terminal) and the input power connector
• Current consumption, power and energy consumption
  derived from the voltage.
• Hardware connected to an oscilloscope.

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The measuring circuit

• Based on INA110 instrumentation amplifier
• fast settling time and high slew rate device.
• Two resistors used low power mode and Tx/Rx
  mode.
• Test performed by a square waveform of 1 kHz and
  of 5 V amplitude at the input of the INA 110
  connected through an attenuating resistive
  divider circuit.
• Good precision and low distortion for conducting
  measurements at the edges.

INA110 main characteristics INA110 main characteristics
Bias 50 pA max
Settling time (Vout 20V) 3 us to 0.1
CMRR 106 dB min
Gain 1, 10, 100, 200, 500
Input impedance 5x1012 ohm 6pF
Slew Rate 17 V/us
Small signal BW 470 kHz (Gain 100)
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Board measurement results

• Preliminary notes
• The CC1010 had a processor built in and therefore
  the CPU on that board could be put into sleep
  mode.
• CC chipcon class presented higher sensitivity
  than TR1001.
• CC1000 and CC1010 boards were configured with the
  oscillator ON in low power mode ? shorter
  switching time
• (2ms activation if OFF)

Boards current and power consumption
Current mA Current mA Current mA Power mW Power mW Power mW
SL RX TX SL RX TX
TR1001 0.005 4.8 12 0.015 14.4 36
CC1000 0.11 10 11 0.33 30 33
CC1010 0.15 26 26 0.45 78 78
Boards switching energy
Switching Energy uJ Switching Energy uJ Switching Energy uJ Switching Energy uJ Switching Energy uJ Switching Energy uJ
SL to RX SL to TX RX to SL TX to SL RX to TX TX to RX
TR1001 8.82 25.2 0.116 2.83 25.2 8.85
CC1000 19 20.5 0.7 0.75 22.4 21.4
CC1010 45.8 47.75 1.83 1.93 61.43 61.61
Switching Times us Switching Times us Switching Times us Switching Times us Switching Times us Switching Times us
SL to RX SL to TX RX to SL TX to SL RX to TX TX to RX
TR1001 700 700 10 10 700 700
CC1000 850 850 10 10 850 850
CC1010 1600 1600 10 10 850 850
Boards switching times
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Phase 2 Switching energy assessment

• The values obtained are applied to the SMAC
  protocol
• SMAC is normally used as benchmark against other
  novel architectures
• Results obtained by using the OmNet simulator

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The SMAC protocol

• SMAC divides time in two periods active time and
  sleeping time
• Active period SYNC period for node sync
  update, Request To Send (RTS), Clear to Send
  (CTS).
• Communication establishing
• neighboring nodes synchronize to the start of
  the active period then local broadcast of SYNC
  packets.
• Data message exchanges follow the
  RTS/CTS/DATA/ACK
• ?nodes switch between different states
  periodically.

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Simulation setup

• Three nodes and one gateway in a line
• Node 3 Source Node1 Node2 Forwarder
  Gateway Destination
• nodes communicate with direct neighbours only.

• Results averaged between node2 and node1 values
  (higher node switching activity)
• 13 independent simulations of 20 minutes each.
• 10 independent random seeds for clock skew and
  offset inaccuracies.
• Traffic load regulated by Node 3
• 16 bytes packet
• Generation rate 60s(low traffic) and 2s (high
  traffic).

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Performance evaluation metrics

• Energy TX spent by per node per bit
  transmitted
• Energy Switch spent per node for the total
  number of transitions of two consecutive states
• Energy Sleep energy spent by one node during
  the time of inactivity referred to as the
  sleeping state
• Total consumption per node all previous metrics
  plus RX energy and idle listening.
• Duty cycle changed by varying the node active
  period

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Simulated results (1) Total consumption
Low traffic

• The simulations ended after 50 packets were
  correctly relayed from source to destination
• Preliminary results
• little increase of consumption in high data
  traffic conditions
• 2) Higher energy consumption profile of CC
  family than Tr1001 due to
• The processor built in
• The oscillator left ON in low power mode
  (oscillator OFF ? gt5mA current consumption to
  wake-up)

High traffic
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Simulated results (2) Low traffic condition
Switching energy as percentage of the total
consumption

• switching energy between sleeping energy and
  energy TX
• Switching energy can be higher than the energy
  TX.
• 1.7 duty cycle lower bound of due to an
  intrinsic operational limit of SMAC.
• Other existing protocols that can work below 1
  duty cycle (e.g. BMAC)

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Simulated results (3) High traffic condition
Switching energy as percentage of the total
consumption

• Maximum switching energy above 6 for 1.7 duty
• E.g. 5 of 2 years ?36 days estimation error
• Oscillator ON causes higher sleeping energy of CC
  family thanTR1001.
• Expected higher of switching energy for duty
  cycle lower than 1.7

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Considerations and guidelines

• Considering 5 as the lower bound of consumption
  significance
• TR1001 and CC1010
• Switching energy to be computed if duty cycle
  3 and 3.6 respectively
• CC1000
• Switching energy to be computed if duty cycle
  2.7
• TR1001
• Sleeping energy negligible for duty cycle 2
• CC1000 and CC1010 in low data traffic
• transmitting energy significant if duty cycle
  2.5.
• Similar energy consumptions may have greatly
  different energy usage composition
• ? The choice of a protocol to use is not only
  based on the application but also on the radio on
  board

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Conclusion

• EYES node direct measurements on switching
  energy for Tr1001, CC1000, CC1010
• Measurements applied to the SMAC protocol
• Considerations and protocol assessment guidelines
  derived
• In low duty cycle sensor-nets, the switching
  energy should be computed together with
  transmitting, receiving and sleeping energies
• Switching energy expected to be more significant
  for duty cycle tends to 1 or lower (e.g. BMAC)
• The results help improving
• MAC protocol evaluation process
• Decisions relating to the judicious
  protocol/hardware choice for an specific set of
  sensor-nets applications
• Future work activities could include the
  investigation of TDMA protocols that allow lower
  node duty cycle and more complex topologies.

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Thank you for your kind attention!Questions
are welcome!
Thank you