radio-triggered wake-up capability for sensor networks
DESCRIPTION
Radio-Triggered Wake-Up Capability for Sensor Networks. Soji Sajuyigbe Duke University. A presentation of the paper: L. Gu and J. A. Stankovic. Radio-Triggered Wake-Up Capability for Sensor Networks. In IEEE Proceedings of RTAS , 2004. Slides adapted from: - PowerPoint PPT PresentationTRANSCRIPT
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Radio-Triggered Wake-Up Capability for Sensor
Networks
Soji SajuyigbeDuke University
Slides adapted from:
Wireless Sensor Networks Power Management Prof. John Stankovic, CS Dept, Univ. of VirginiaReal-Time Communication in Wireless Sensor Networks Richard Arps, Robert Foerster, Jungwoo Lee, Hui Cao
A presentation of the paper:L. Gu and J. A. Stankovic. Radio-Triggered Wake-Up Capability for Sensor
Networks. In IEEE Proceedings of RTAS, 2004.
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Scheme Design GoalsScheme Design Goals
• Provide energy efficient sensing coverage for a geographic area covered by sensor nodes– Extend system life
• Reduce total energy consumption• Minimize sensor wake-up periods
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Power Costs - Examples
Power Costs - Examples
• Motes– ATmega 128 – six working modes with
different energy saving features• Most aggressive sleep can be very small %
of active working mode– Working – 8 mA– Sleep – 100 microA
– Radio• 10 microA sleeping• 7.5 mA Rcv• 12 mA Tx
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Power Management Schemes
Power Management Schemes
• Scheme discerns application and decides efficient wake-up/sleep schedule– Should not trade-off performance– Application Specific– Often involves collaboration with other nodes in
network– Needs time synchronization service
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Hardware layerHardware layer
• Turn off/on– CPU – Memory– Sensors– Radio (most expensive)– Fully awake ………… Deep Sleep
• SW ensures a node/components are awake when needed
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Power Management – Communication
Coverage
Power Management – Communication
Coverage
Minimum awake - still communicate
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Sensing CoverageSensing Coverage
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Nodes present in Network
Nodes present in Network
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Possible Solution (1)Possible Solution (1)
• Periodic wake-up– Each (non-awake) node has a sleep/wakeup duty cycle
based on local timer• Listen for stay awake message
– Most current systems use this technique– Application dependent, often complicated, wastes
energy• E.g., correct duty cycle depends on speed of
targets, sensing ranges, types of sensors, …• May miss wakeup call
Awake Sleep
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Possible Solution (2)Possible Solution (2)
• Special low power hardware stand-by component that (always) listens for a wakeup beacon (not the full radio component)– Uses extra energy (but not as much as full radio
component)
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Other Related WorkOther Related Work
• UCBerkeley and Intel Research– Wake-up messages awakens whole network– In every 4 sec node must be awake for 100ms – Timer-based protocols and special hardware needed
• SMAC– Nodes gauge channel and sync periodically with
neighbors– Duty cycle of 30-40% achieved
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Radio-Triggered SchemeRadio-Triggered Scheme
• Just-In-Time Wake-up Capability– A node does not wake up until it is needed– It uses no active listening energy– Uses radio-triggered hardware that extracts energy
from the electromagnetic energy in the wakeup signal itself
– Not RFID – they employ powerful readers to send strong radio signals
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Application ScenarioApplication Scenario• A small number of nodes stay awake• Most of the network sleeps• Rare events
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Application ScenarioApplication Scenario• Awakened nodes detect an
event• Messages are sent to wake
up other nodes
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Radio-Triggered Requirements
Radio-Triggered Requirements
• Node should turn ON immediately• No false wake-ups• Should not miss wake-up calls• While sleeping, expend same amount of energy
as schemes without radio-triggered
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Radio-Triggered Hardware
Radio-Triggered Hardware
• lone antenna• special radio frequency• low cost
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Basic Radio-Triggered Hardware
Basic Radio-Triggered Hardware
Task:• collect EM energy• distinguish trigger
signals from others• drive ‘start’ voltage
0.6 V
Wake up!
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Effectiveness of basic circuit
Effectiveness of basic circuit
2
2(4 )s s r
r
PG GP
D
• Only 10 ft transmission secured if Berkeley Mica motes used
Gain needed to get 0.6V at Vout
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Improve basic circuit to extend range
Improve basic circuit to extend range
• Reduced voltage threshold requirement will increase range– Use comparator to measure output voltage
– If Vin too low, amplifier can be employed.
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Scheme EvaluationScheme Evaluation
• Application scenario– 1000 random motes deployed– 10 events daily, each lasts 2 minutes– Vehicle tracking Application– Nodes use two 1600mAh AA batteries
• Compare the following schemes– Always-on– Rotation (wake-up/sleep)– Radio-Triggered
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Solution – Is it worth it? Solution – Is it worth it?
• Scheme I: Always-on (No power management)– The node is on and actively
sensing until it is out of power
– 1% of the energy is used to track vehicles, 99% is used in a peeking state (uselessly sensing for potential passing vehicles)
– Lifetime 3.3 days
Always-on
Waiting99%
Tracking1%
Energy wasted!!!
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Solution – Is it worth it? Solution – Is it worth it?
• Scheme II: Rotation-based (Periodic wake-up)– Nodes are awakened
wirelessly by wake-up messages
– Duty cycle 4.7%– 21% of the energy is used
to track vehicles, 7% used in sleeping mode, and 72% is used in peeking state
– Lifetime 50 days
Rotation-based powermanagement
Wai ti ng72%
Sl eep7% Tracki ng
21%
Energy wasted!!!
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Solution – Is it worth it? Solution – Is it worth it?
• Scheme III: Radio-triggered– Nodes keep sleeping until
events of interest happen– Nodes are awakened
wirelessly by wake-up messages
– 74% of the energy is used to track vehicles, 26% used in sleeping mode (minimal cpu energy)
– Lifetime – 178 days
Radio-triggered powermanagement
Tracki ng74%
Sl eep26%
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Network Lifespan Comparison
Network Lifespan Comparison
Comparison of lifespan
0
50
100
150
200
250
always-on rotation scheme radio-triggered
Lifespan (days)
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Circuit Design ImprovementsCircuit Design Improvements
• Add capacitor and transformer– Capacitor rise time and transformer introduce
latency
– Three times operating distance can be realized (30 ft) if 5ms latency acceptable
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Circuit Design ImprovementsCircuit Design Improvements
• Add Amplifier– Use amplifier with low sleep current (880nA:
0.8% of 100uA)
– Does not compromise functionality; will help increase range
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ConclusionsConclusions
• Extracts energy from the radio signals
• Hardware provides wake-up signals to the network node without using internal power supply
• Adequate antenna : does not respond to normal data communication, not prematurely wake up
• Highly flexible and efficient – Zero stand-by power consumption and timely wake-up
capabilityThis slide courtesy: Real-Time Communication in Wireless Sensor Networks Richard Arps, Robert Foerster, Jungwoo Lee, Hui Cao
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Questions?Questions?