Mobile Networking for Smart Dust

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Mobile Networking for Smart Dust

• J.M. Kahn, R.H. Katz and K.S.J. Pister
• Department of Electrical Engineering
• and Computer Sciences
• University of California, Berkeley
• Berkeley, CA 94720
• Supported by DARPA MTO MEMS Program

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Outline

• Smart Dust
• What is it?
• Applications
• Power Management
• Delivery and Interrogation
• Smart Dust Networking
• Radio-frequency communication
• Optical communication passive dust mote
  transmitters
• Optical communication active dust mote
  transmitters
• Summary

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Smart Dust

• A dust mote is an autonomous node incorporating
  sensing, computing, communications and a power
  source in a mm3 volume
• A collection of dust motes is dispersed
  throughout an environment
• Dust motes use wireless communication to relay
  information to a base station over distances of
  10s to 1000s of m

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Smart Dust Mote
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Applications of Smart Dust

• Civilian
• Surveillance
• Meteorological or geophysical monitoring
• Non-invasive measurement
• Measurement in hostile environments
• Military
• Stealthy monitoring of hostile environments
• Perimeter surveillance
• Chemical or biological monitoring
• Identification of friend or foe

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Power Management

• Sources
• Solar cells
• Thermopiles
• Storage
• Batteries 1 J/mm3
• Capacitors 1 mJ/mm3
• Usage
• Digital control nW
• Analog circuitry nJ/sample
• Communication nJ/bit

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Delivery and Interrogation

• Delivery Systems
• Manual
• Micro air vehicle
• Projectile
• Wind-borne (maple seeds)
• Interrogation
• Hand-held binoculars
• Micro air vehicle

MAV built by MLB Co.
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Radio-Frequency Communications

• Pros
• Long range
• Line-of-sight path not required
• Not severely affected by rain, fog or atmospheric
  turbulence
• Cons
• Antenna may be too large for dust motes
• Requires modulator, demodulator, filtering (power
  consumption)
• Requires complex multiplexing scheme (TDMA, FDMA,
  CDMA)

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Corner-Cube Retroreflector

• Fabricate CCR using MEMS technology.
• Light striking within about 30 of body diagonal
  undergoes 3 bounces and returns to source in a
  narrow beam (ltlt 1).
• Can deflect one mirror electrostatically,
  modulating return beam at up to 10 kbps.
• Dust mote can transmit passively without
  radiating energy and without aiming beam.

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First-Generation Dust Mote
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Optical Communication UsingPassive Dust Mote
Transmitters
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Optical Communication UsingPassive Dust Mote
Transmitters (cont.)

• Requires each dust mote to have a line-of-sight
  path to the base station.
• Uplink transmissions are multiplexed using
  space-division multiplexing.

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Optical Communication UsingPassive Dust Mote
Transmitters (cont.)

• Protocol
• Dust motes are asleep.
• Base station broadcasts a wakeup/query, then a
  periodic interrogating signal synchronized to its
  camera.
• Dust motes wake up, transmit simultaneously to
  base station, synchronized to its camera.
• Reliability
• Dust mote positions and orientations are random,
  and some are not in field-of-view of base
  station. To insure coverage, use an excess of
  dust motes.
• Base station is only single point of failure.

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Optical Communication UsingPassive Dust Mote
Transmitters (cont.)

• Pros
• Dust motes need not radiate power, nor steer beam
• Exploits asymmetry powerful base station,
  low-power dust motes
• Utilizes space-division multiplexing
• Only baseband electronics are required
• Cons
• Requires line-of-sight path to base station
• Short range (up to about 1 km)
• Bit rate limited to about 10 kbps
• Affected by rain, fog, atmospheric turbulence

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Active Dust Mote Transmitter
Two-axis beam steering assembly
Active dust mote transmitter

• Beams should have divergence ltlt 1º and be
  steerable over a hemisphere.

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Optical Communication UsingActive Dust Mote
Transmitters

• Base station uses CCD or CMOS camera (up to 1
  Mbps)
• Using multi-hop routing, not all dust motes need
  to have a line-of-sight path to the base station.

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Optical Communication UsingActive Dust Mote
Transmitters (cont.)

• Minimizing transmitted energy/bit
• Dust mote should transmit in short bursts at high
  bit rate
• Link Acquisition
• Need protocols for dust motes to aim their
  directional transmitters at other nodes
• Dust motes should execute raster scan using a
  narrow (not wide) beam

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Optical Communication UsingActive Dust Mote
Transmitters (cont.)

• Link Non-Reciprocity
• Arises because dust motes use directional
  transmitters but non-directional receivers
• May cause a dust mote to waste power transmitting
  to nodes unable to receive from it. A dust mote
  should transmit only to nodes that acknowledge
  its transmissions.
• May cause collisions at dust motes during
  mote-to-mote communications.
• Routing
• How to acquire, propagate and update routing
  information?

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Optical Communication UsingActive Dust Mote
Transmitters (cont.)

• Pros
• Longer range than passive links (up to about 10
  km)
• Higher bit rates than passive links (up to about
  1 Mbps)
• With multi-hop, avoids need for every dust mote
  to have line-of-sight path to base station
• Utilizes space-division multiplexing
• Only baseband electronics are required
• Cons
• Requires protocol to steer directional
  transmitters
• Requires higher power than passive transmitter
• Affected by rain, fog, atmospheric turbulence

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Atmospheric Turbulence

• Enhancing signal detection reliability
• Adaptive optics on imaging receiver
• Spatial receiver diversity (multiple receivers)
• Temporal receiver diversity
• Maximum-likelihood sequence detection based on
  Markov model of scintillation process
• Interleaving and forward error correction

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Summary

• Smart dust motes incorporate sensing,
  computation, communications and power in a mm3
  volume.
• Free-space optical communication offers
  advantages in terms of size, power and network
  throughput.
• Passive dust mote optical transmitters
• Use corner-cube retroreflector
• Consume very little power
• Require line-of-sight path to base station
• Active dust mote optical transmitters
• Use laser and beam-steering mirror
• Enable higher bit rates, longer ranges, multi-hop
  routing