Driving%20the%20Power%20Out%20of%20Wireless%20Sensor%20Networks

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Driving the Power Out of Wireless Sensor Networks

• Jason Hill

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Overall Mote Vision

• Integrate computation, communication and sensing
  into a single unit
• Advanced behavior emerges from collection of
  simplistic devices
• Exploit peer-to-peer architectures that scale to
  thousands of nodes
• Allow seamless integration with physical world
• Robust networking achieved through redundancy
• Short range communication reduces power
  requirements and conserves bandwidth

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Example uses

• Env. Monitoring, Conservation biology, ...
• Precision agriculture, land conservation, ...
• built environment comfort efficiency ...
• alarms, security, surveillance, treaty
  verification ...
• Civil Engineering structures response
• condition-based maintenance
• disaster management
• urban terrain mapping monitoring
• Interactive Environments
• context aware computing, non-verbal communication
• handicap assistance
• home/elder care
• asset tracking

CENS.ucla.edu
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Outline

• Hardware generations
• Mote Success Stories
• Power is King Discussion of power saving
  techniques
• Specialized hardware
• Spec Node
• Specialized protocols
• Low power listening
• RF Wake-up
• Time Synchronized Comm.
• Current Status

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Design Lineage

• COTS dust prototypes (Kris Pister et al.)
• weC Mote (30 produced)
• Rene Mote (850 produced)
• Dot (1000 produced)
• Mica node (current, 5000 produced)
• Spec

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Mote Success Stories
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29 Palms Military Vehicle Tracking
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Intel Developers Forum

• 800 Nodes
• Live demo
• Displayed networktopology in lights

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Great Duck Island
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Power Saving Techniques

• Improve performance of communication operations
  (hardware)
• Radio power consumption
• Transmission bit rate
• Efficiency of protocol implementation
• Streamline protocols for power savings (software)
• Flexible, application specific protocols
• Trade latency and bandwidth for decreased power
  consumption

Must do both!!!
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Spec Requirements

• Drastically reduce power consumption, cost and
  size
• Maintain a tight integration between processing,
  communication, and sensing that allows
  cross-layer optimizations
• Allows for rich interfaces to hardware
  accelerators and flexible resource pools
• Provides
• Efficiency
• Through specialized concurrency mechanisms and
  optimal hardware accelerators
• Flexibility
• By using software to compose basic protocol
  building blocks into application specific
  protocols with rich interfaces

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The Spec Architecture

• Single CPU for Base band, OS and Application
• Shared system resources can be divided between
  system components dynamically
• High bandwidth, flexible interfaces can be
  exposed across system components
• Allows applications access to fine-grained system
  control
• Hardware accelerators to support key sensor
  network challenges
• Communication, synchronization, power management,
  concurrency
• Shared memory interface model

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General Architecture Diagram
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Spec Primitives

• Integrated Transmitter
• 800-gt1100 MHz transmitter
• FM/AM
• Inductor and Reference crystal are only external
  components
• Consumes 1 mW _at_ 2.7 V minimum voltage
• .5 mW TX power
• Targeting 300 uA receive mode
• -95 dBm receiver sensitivity
• Same sensitivity as RFM at 1/10 power
• Tunable IF (Low)
• lt100 us turn-on time
• Designed by Al Molnar

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Spec Primitives (cont.)

• Integrated ADC
• Ultra low power 8-bit ADC
• 27 pJ per sample (1000x improvement over industry
  standard)
• Designed my Mike Scott
• Register Windows
• Allows for fast interrupt support
• With early versions of TinyOS, 50 of CPU energy
  consumption went to saving register sets
• 28x reduction in interrupt overhead vs. Mica

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Spec Primitives (cont.)

• Encryption Support
• Stream based, LFSR based cipher
• Automatic generation of random pad
• Encryption automatically performed during
  transmission and reception
• Allows for efficient secure communication and
  authentication
• Encrypted MAC can serve as both CRC check and
  authentication signature
• Communication Accelerators
• Hardware Start symbol detection
• Automatic timing extraction and synchronization
• DMA memory engine

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Spec Layout
2.5mm

• IO Pads
• RAM blocks
• MMU logic
• Debug logic
• ADC
• AVR CPU Core
• RF Frequency Synthesizer
• Transmitter

.25 um CMOS
Core Area only 50 full
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Spec
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Communication Interface

• Hardware provides message-level AM interface
• Same functionality only implemented in hardware
• gt 5000 x cost reduction
• Hardware handles
• Message send command with TOSMsgPtr
• Hardware signals
• Message arrival event with TOSMsgPtr
• CPU communication overhead dropped from approx.
  2MIPS down to 0.

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Spec Demonstration
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(No Transcript)
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Power savings through adaptive protocols
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Trade latency for power

• Low power receiving
• Reduce receiver power consumption while
  introducing minimal additional transmitter
  overhead
• Total Power Power of Receiver Send Rate
  Energy of Transmitter
• Sample briefly to detect activity

ms
ms
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29-Palm low-power listening

• Frequent messages expected
• 2-3 per second possible
• 10 duty cycle selected for receiver
• Channel Check in 30 us
• 300 us extra transmission required
• 10x radio power consumption for receiver
• Bonus 50 reduction in CPU usage

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IDF RF Wake-up

• Expected message frequency near zero
• Ultra-low power network sleep state
• Network can be woken from uA sleep state within
  seconds
• Flexible radio use reduces check time from 100
  ms to 50 us over packet based protocols
• 334x transmission cost increase for 30 byte
  message

ms
ms
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Time Synchronized Communication

• Global time used to schedule communication
• Caps transmitter energy requirements
• Accuracy of timing determines worst-case overhead
• Precise packet timing leads to lt ms
  synchronization accuracy
• Still trading latency for power

ms
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GDI GSK Power

• GDI uses low-power listening varrient
• Periodic checks every 500 ms for 10 ms -- 5 Duty
  Cycle
• Message preamble 1200 bytes long prior to
  sending actual data
• Expected message interval 10 mintues
• Expected 3 month lifetime
• GSK uses time windows for communication
• Periods of active communication followed by sleep
• Time intervals in seconds
• Resynchronization required during active periods

Both can used unmodified routing algorithms.
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Dust Inc.s HDK

• Combines multiple power saving techniques
• Low-power listening used for infrequent
  configuration and emergency messages
• TDMA based message scheduling used for regular
  data collection messages
• Central server determines TDMA schedules and
  routing topologies

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Putting it all together

• Apply combined optimizations into typical
  application
• Sample application that
• Check sensor every 4 seconds
• Collects data every 5 minutes
• Aggregates data from child nodes
• Checks for Alarm conditions every 4 seconds
• 2 AA battery power supply

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Sample Application Performance
Samples 21600
Reports 288
Communication Events 1728
Alarm Checks 21600
ADC Conversion 2.4 mJ/Day
Communication 298.1 mJ/Day
Synchronization 103.7 mJ/Day
Alarm Checks 254.0 mJ/Day
Idle cost 518.4 mJ/Day
Total 1176.6 mJ/Day
Pair of AA Batteries 1.17E07 mJ
Expected Lifetime 27.2 Years
x
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Questions?