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SMART TRANSMITTERS &
RECEIVERS
FORUNDERWATER FREE-SPACE
OPTICAL COMMUNICATION
Presented by
Christy
4sne!"#$
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CONTENTS
Introduction
Underwater optical channel
Smart Receivers
Smart Transmitters
Experimental Results
Benefits
Disadvantages
Conclusion
References 2
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INTRODUCTIONUnderwater communication is of great interest
for military industry and scientific communities!"i#er optic and copper ca#ling can #e used for
stationary devices a wireless lin$ is usually
desira#le!Radio fre%uencies are heavily attenuated in sea
water!
&coustic communication suffers from low datarates!
"or short range lin$s free space optical
communication is promising alternative!3
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Underwater free space optical communication
ta$es advantage of '#lue green optical window(
of relatively low attenuation of #lue greenwavelength of electromagnetic spectrum
underwater!
)aser #ased systems can #e used for extended
ranges and high data rates!
)ed #ased systems have #een demonstrated for
low cost low power and compact systems!
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In this paper we propose a concept of smart
transmitters and receivers!
The smart receivers have wide "*+ and arecapa#le of detecting angle of arrival of signal in
order to ad,ust "*+ towards desired signal!
Smart transmitters are capa#le of using thisinformation to electronically steer its o-p #eam
towards a particular direction!
&lso capa#le of estimating water %uality fromits #ac$scattered light collected #y its co.
located receiver!
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UNDERWATER OPTICAL C%ANNEL
Underwater free space optical channel is very
different from atmospheric channel!
"rom an optical comm! perspective the /
important properties are 0 #eam attenuation
coefficient volume scattering function and
al#edo!
)ight interacts with water and materials
dissolved in it in 1 different ways0 sorption
2 scattering!6
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e'( 'tten)'ti*n !*e++i!ient 0
&mount of energy a#sor#ed or scattered from an
incident power per unit distance!Denotes the total energy lost!
Sum of a#sorption and scattering coefficient!
A,bed*0
Ratio of scattering coefficient to #eam attenuation
coefficient !Denotes pro#a#ility that a photon will #e
scattered rather than a#sor#ed!
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V*,)(e s!'tterin +)n!ti*n0
Defined as the fraction of scattered power to
incident power
3ater type &ttenuation coeff!45-m6
Clear ocean 7!581
Coastal ocean 7!/99:ar#or water 1!598
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SMART TRANSMITTERS
Should have following characteristics0
5; Increased directionality
1; Electronic switched #eam steering
Desin
Similar to receivers transmitters also have
truncated hexagonal pyramid! Unli$e receiver each )ED is coupled with its own
lens that converges wide "*+ of )ED to narrower
#eam in a particular direction! 9
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Me!h'nis( *+ be'( steerin
Each )ED is uni%uely addressed and driven!
This allows the modulator to select an output
direction!
This forms the mechanism of simple switched
#eam steering at the transmitter!
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SMART RECEIVERS
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Desin !*nsider'ti*ns
5; Lens 't the re!ei.er0
Existing optical receivers uses only photodiodes!=roposed design uses an array of lenses as well
as an array of photodiodes!
1; An,e *+ 'rri.', esti('ti*n0
The intensity of light received #y each
photodiode can #e used to roughly estimate angleof arrival of light!
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3]Ph*t*di*de */0 !*(binin1
Important consideration for the performance of
the system!Simplest interface to the array of photodiodes is
to connect in parallel!
But results in low #andwidth!
1 com#ining techni%ues 0
E2)', 'in !*(binin 3EC5Se,e!ti*n !*(binin3SEL5
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ENEFITS
>on mechanical pointing 2 trac$ing on a moving
underwater vehicle
?aintaining lin$ with stationary node as an
underwater vehicle does a drive #y
=roviding sensory information to underwater
vehicles
Duplex multiuser system
*ptical #ac$scatter estimation to assess water
%uality
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DISADVANTAES
=oint to point communication
=oint to multipoint communication is notpossi#le #ecause of the use of led or laser!
System may receive from two differentsystem #ut it is not possi#le to transmit to
two different system!
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CONCLUSION
Results show that design is capa#le of
acting as a smart system!
This smart transceiver proposal reduce
pointing and trac$ing needs which
otherwise pose a ma,or pro#lem with the
communication platforms used #y the
unmanned devices underwater!
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REFERENCES
@5;Simpson :ughes Aohn " 'Smart transmittersand receivers for underwater free-space optical
communication.
@1;?!&! Chancey Short range underwater optical
communication links, ?asters Thesis >orth
Carolina State University 1778 p! 1 Aan!177!
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THA
NKY
OU
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