my seminar-1.pptx

7/25/2019 my seminar-1.pptx

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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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my seminar-1.pptx