seminar ppt for smart transmitter and receiver for under water free space optical communication

5/21/2018 Seminar Ppt for smart transmitter and receiver for under water free space optical communication

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BY,

SIJI M T

GUIDE : RENJISHA E

RAJAN

SMART TRANSMITTERS ANDRECEIVERS FOR UNDERWATER

FREE SPACE OPTICAL

COMMUNICATION


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INTRODUCTION

19-Aug-14smart transmitter and receiver for under water

free space optical communication2

Underwater vehicles, sensors, and observatoriesrequire a communication interface.

Underwater Free space optical communication-

Promising alternative for Short range links. Point to point.

A new optical front-end for underwater free-space

optical communication- smart transmitter & receiver.


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Benefits of smart optical systems



Non-mechanical pointing and tracking on amoving underwater vehicle.

Maintaining link with a stationary node as anunderwater vehicle does a drive-by

Providing sensory information to underwatervehicles

Duplex multi-user system.

Optical backscatter estimation to assess waterquality.

Electronic Switched Pointing & Tracking.


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Properties of under water

channel



Beam attenuation coefficient(c()): ratio of energyabsorbed or scattered from an incident power per unit

distance.

It denotes total energy lost

Single-scattering albedo(o): ratio of scattering

coefficient to beam attenuation coefficient .

it denotes the probability that a photon will be

scattered rather than absorbed. Volume scattering function: fraction of scattered

power to incident power as a function of direction

scattered into a solid angle .


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A 3.66m long,1.22m wide,1.22 m tall indoor water tankconstructed .

Maalox-commercial antacid-scattering agent -controls

attenuation coefficient of water.

Nigrosin dye - control the albedo.19-Aug-14

smart transmitter and receiver for under water



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Figure : Relationship between attenuation

coefficient and SNR for experiments in laboratory

test tank.




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Smart Receiver



Goal quasi- omnidirectional system to reducepointing and tracking requirement.

characteristics

Increased field of view Angle of arrival estimation


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Design



consists of a 3-D spherical array of lenses all focusingto a 2-D planar array of photodiodes.

A prototype has been constructed using seven

lenses and seven photodiode.

Lens at the receiver :

Existing terrestial optical front-end arraysphotodiode arrays with no lenses a single lens with multiple photodiodes multiple lenses focusing on separate photodiodes.

Proposed designarray of lenses & photodiodes withmultiple combination of optical path.


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Quasi-omnidirectionality : photodiode array under

middle layer increases the FOV from 5-40degree.

Addition of outer lenses at 130 with respect to middlelayer increase the FOV to 120degree.

Angle of Arrival Estimation: The intensity of light

received by each photodiode can be used to roughly

estimate the angle of arrival of light.

Photodiode output combining:

Connect the array of photodiodes in parallel.

An ideal combining techniquemaintain bandwidth

minimize noise

maximize SNR


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Linear diversity combining techniques

Equal Gain Combining(EGC)

Maximum Selection Combining(SEL)


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Smart Transmitter

19-Aug-14



The smart transmitter has the followingcharacteristics:

Increased directionality

Electronic switchedbeamsteeringDesign

Consists of a truncated hexagonal pyramid with

seven LEDs.

Each LED is coupled with its own lens that

converges the wide FOV of the LED to a narrower

beam in a particular direction.


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19-Aug-14



Each LED is uniquely addressed and driven, which

allows the modulator to select an output direction.

This forms the mechanism for a simple switched

beam steering at the transmitter.

CDMA Coding ( Code division multiple access)

Asynchronous method for multiple access

scheme.

Incoherent optical detection and processing make

typical RF maximum length and Gold codesequences not ideal.


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19-Aug-14



The on-off-keying modulation methods in optical

communication are unipolar as opposed to the bipolar

modulation required by Gold codes. Instead optical CDMA typically uses prime codes.

A large code sequence will decrease overall BW but

allow for more users with a corresponding increase in

SNR.


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EXPERIMENTAL RESULTS

19-Aug-14



Prototype lens-photodiode arrays and LED-arrayswere constructed for the receiver and transmitter

front-ends to collect data.

Receiver - Designed to pre amplify and digitize thereceiver outputs.

Transmitter - Designed to receive up to seven

different streams of data and drive up to seven

different LEDs on the LED-array.


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19-Aug-14



Under water channel used was 3.66m long laboratory

water tank.

Channel condition are adjusted by controlled addition

of liquid maalox.

The resulting attenuation coefficient was measured.

Experiments are conducted for characterizing thereceivers and transmitters & to demonstrate their

capabilities.


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19-Aug-14



Characterization of the Receiver Lens-photodiode

Array:

Experiments were conducted for the receiverpointed in all directions and intensities were

observed at all photodiode outputs stored as a

function of the spherical co-ordinates.

A pan and rotate system. constructed using digital

servos.

Seven amplified photodiode outputs digitized using

a simultaneous 8 channel digitizer.


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19-Aug-14




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19-Aug-14



Angel of arrival estimation:

Estimating the direction of arrival of the incident light

based on the relative output powers at eachphotodiode.

Outputs of receiver at each instant are sorted and

compared with receiver output patterns.

Angle of best match is taken as the estimated angle.


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19-Aug-14



Backscatter Estimation:Transmitter

A co-located receiver to estimate the attenuationcoefficient.

Can estimate the quality of water.

adaptively change its transmit power, data rate,code rate or other parameters.

challenge is that the return beam frombackscatter , depends on the attenuation

coefficient of the channel. Remedysending a higher power training

sequence it increasing the receiver gain.


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19-Aug-14



Figure : Results of the backscatter

estimation experiment


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CONCLUSION

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Results show that design is capable of acting as a smart system. Backscatter estimation experiment demonstrates linear

relationship between return beam intensity and channel

attenuation coefficient.

It helps to estimate water quality. Smart Receivers

increased field of view.

estimate angle of arrival.

Transmitters :

quasi omnidirectional.

allow electronic switched beamsteering.


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REFERENCE

19-Aug-14



1] C. Pontbriand ,N. Farr, J. Ware, J. Preisig, and H. Popenoe,

Diffuse high-bandwidth optical communications, in Proc.

OCEANS Conf. 2008,Quebec, Canada, Sept. 15-18 2008.

2]B. Cochenour, L. Mullen, and A. Laux, Phase Coherent

Digital Communications for Wireless Optical Links in TurbidUnderwater

Environments, in Proc. OCEANS Conf. 2007, Vancouver, BC,

Canada, 2007.

3] F. Hanson and S. Radic, High bandwidth underwater opticalcommunication, Applied Optics, vol. 47, no. 2, p. 277, Jan.2008.


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19-Aug-14



seminar ppt for smart transmitter and receiver for under water free space optical communication

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