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Design and Implementation of Optical
Wireless Communications with
Optically Powered Smart Dust Motes
Dominic C. O Brien,Jing Jing Liu
,
CONTENTS
1.Introduction
2.Micromachine communication network
3.Base station design
4.Smart dust motes
5.System results
6.Conclusion
INTRODUTION
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Providing connection with micro machines and
smart dust are challenging
Integrated circuits with wireless connection are
preferred
Optical wireless communications is an attractive
option
for low data rate communications modulated retroreflectors are used
Low speed communication for smart dust without
tracking
OVERVEIW
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according to fig1 Base Station is situated
above a number of Smart Dust Motes.
Light from the BS falls on a particular mote
using holographic beemsteering system.
The light illuminates the SDM, and modulated
to provide a downlink from the BS to the SDM
A Modulated Retro-Reflector on the SDM
reflects light back to the BS.
BASE STATION DESIGN
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BS illuminate the SDM to provide power,
intensity for the SDM downlink and power for
uplink to operate.
Holographic beam steering used for
maximizing intensity.
possibility to alter the divergence of beams,
and correct for aberrations.
Base station
Optical design and link budget modeling
Optical system layout
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Light from a 670nm laser is polarized and
illuminates the SLM.
The SLM is arranged for binary phase
modulation.
Resulting wave front is Fourier transformed
using a Fourier Lens.
Two lenses are used to magnify the steering
angle, to create a total view of 30 degrees.
B. Intensity and link budgets
Three constraints for correct operation of SDM
1.illumination intensity from the beam to
power the SDM
2. sufficient link margin for the downlink
3.sufficient link margin for the uplink.
The intensity at the SDM is
m:order of beam
from BS
PT:transmitted
power
r:distance from BS to
SDM
Light passes through the aperture of the modulator, is
retro-reflected and passes back through it once more
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power that passes back through the aperture
to be ’re-emitted’and propagate back to the
BS,
Πa^2LC :area ofmodulator
R:reflection coefficient of retro
reflector
C. System Operation
 1.Acquisition and tracking
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2.Downlink
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3.Uplink
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4.Network operation
SMART DUST MOTES
The SDM consists of
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power photodiode
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communications receiver
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Modulated retro reflector
LC cells: to form the modulator
LC drive directory
Retroreflectors
Layout of smart dust integrated circuit. The large areas in the
centre are different types of power photodiode. The IC is
5x5mm in size.
Modulated retro-reflector
SYSTEM RESULTS
Downlink and SDM operation
 SDM
was illuminated with a
downlink waveform of avg intensity
3.5 μW/mm^2
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1nF external storage capacitor is
connected
The measured response of a optically powered mote
This shows the SDM operating correctly, and that the successive signals are
translated to operating voltages required for LC cell.
Switching energy is 16pJ/bit for 100pJ.
Electrical power consumption is approximately 100nA at .4V or40nW.
B. Base station tracking
 Tracking error was reduced by making
precorrection to steering angle
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Measuring performance of correction using
rectangular calibration board.
consisting of 90 equally spaced retroreflectors.
Each target was acquired and tracked and
C Uplink operation
shows a waveform of a 32bit/s Manchester coded waveform received by
the base station at a distance of 15 m under low ambient light conditions
and a sampling (frame) rate of 250 samples/s
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The link was operated in a dark room with
different LC voltages at a range of 3m.
The received waveforms that are recorded are
degraded by Inter-symbol Interference (ISI)
Data recovery achieved by using a band pass
filter.
present the SDM and the uplink have been
separately tested, and both show correct
operation
CONCLUSION
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optical wireless technique can communicate
with and power small silicon based systems.
Communication over 10s of metres is
possible using the interrogating beam.
total power consumption of the mote is
approximately 40nW.
integrating the communications modulator
and the si to create a compact dust mote
REFERENES
[1] Specknet collaboration,www.specknet.org,
Accessed Jan 2009.
[2] J. M. Kahn, R. H. Katz, and K. S. Pister, Next
century challenges: mobilenetworking for
”Smart Dust”’ 1999.
[3] Semiconductor Industry Association
www.sia-online.org, Accessed May2009.