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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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