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8/12/2019 Presentation Fnl

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FINAL YEAR PROJECT PRESENTATION

[P1]

STUDY OF OPTICAL OFDM

PRESENTED BY-

MANGI LAL [101055]

MAYANK JOSHI [101058]

MAYUR NAYAK [101059]


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Motivation

Limited Bandwidth Available

Need for high Speed communication OFDM has gained Prominence due to its intrinsic

robustness to frequency selective multipath

fading channels and high spectrum efficiency.


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OFDM

The first proposal to use orthogonal frequencies for

transmission appears in a 1966 patent by Chang of Bell

Labs.

OFDM i.e Orthogonal frequency division multiplexing is a

special class of multicarrier modulation that transmits data

in parallel by modulating a set of orthogonal sub carriers.

Frequency Division Multiplexing Orthogonal Frequency Division Multiplexing


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Optical OFDM

The key idea behind OOFDM is to split a high-data

rate data-stream into a number of low-rate data-

streams that are transmitted simultaneously over a

number of subcarriers. The symbol duration ofthese low-rate data-streams is made substantially

larger , with a goal to increase the immunity of a

system to residual chromatic dispersion.

Optical OFDM are mainly classified into two maincategories

1. Coherent detection.

2. Direct detection


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Usefulness of Optical OFDM

It is used in high speed data transmission such as4-G technology.

It exploits optical bandwidth efficiently .

It is suitable for long- haul transmission because ofits ability to deal with large pulse spreads due tochromatic dispersion.

High speed transmission over multimode opticalfibers.

Improvement of the spectral efficiency .


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Multicarrier Modulation

The basic idea of multicarrier modulation is to divide thetransmitted bitstream into many different substreams and

send these over many different subchannels. Typically the

subchannels are orthogonal under ideal propagation

conditions.

S/PBank of

Modulator

Summer

To

channel

RepeaterFrom

channel

.

.

Bank of

demodulator

.

.

P/SSerial

Symbol

stream

Transmitter

Receiver


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In MCM we need N modulators and demodulators which is

a challenging task.

In 1971 Weinstein and Ebert made an advancement by

using FFT and IFFT algorithm instead of modulators anddemodulators .

This is the basis for OFDM.

(b) Receiver


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During the signal transmission, the problem of ISI occurs

that can be removed by using cyclic prefix.

Cycl ic pref ixrefers to the prefixing of a symbol with a

repetition of the end.

In order for the cyclic prefix to be effective, the length of the

cyclic prefix must be at least equal to the length of the

multipath channel.


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Minimum length of cyclic prefix required is related to the

delay spread. So length = L-1, also :CP > delay spread,

Where ,

CP is cyclic prefix

L is length of channelEffect of addition of CP results in loss in throughput of

system.


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PAPR in OFDM

Presence of large number independently modulated

subcarriers in an OFDM system, the peak value of the system

can be very high as compared to average of the wholesystem.

This ratio of peak to average power value is termed as PAPR.

PAPR = ]|][[|/]|][[|max 22 nXEnXnn


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Optical OFDM

We classify optical OFDM as coherent detection

and direct detection.

Although direct detection has been the mainstayof optical communications during the past two

decades, progress in forward looking research has

unmistakably indicated that the future of optical

communications is coherent detection.


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Coherent Optical OFDM

Coherent optical OFDM (CO-OFDM) represents

the ultimate performance in receiver sensitivity, spectral

efficiency, and robustness against polarization dispersion,but it requires the highest complexity in transceiver design.


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Data OFDMTransmitter

Optical

upconverter

Fiber link Optical

downconverter

OFDM

ReceiverData

Optical amplifier

CO-OFDM system


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Problem Formulation

Analysis of Optical OFDM in high speed

transmission system with high spectral efficiency.


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Time Framing :-P1 :- Basics of OFDM and introduction of Optical

OFDM.

P2 :- Analysis of coherent Optical OFDM.

P3 :- OFDM for multimode fiber system.P4 :- Comparision of different transmission

equipments of coherent Optical OFDM system.


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References Ivan B. Djordjevic and Bane Vasic Orthogonal

frequency division multiplexing for high-speed

optical transmission May 2006 / Vol. 14, No. 9 /

OPTICS EXPRESS 3774

W. Shieh and C. Athaudage Coherent opticalorthogonal frequency division multiplexing

ELECTRONICS LETTERS 11th May 2006 Vol. 42

No. 10

William Shieh and Ivan Djordjevic OFDM forOptical Communications.

Qi Yang, Abdullah Al Amin, and William Shieh

Optical OFDM Basics.

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