FINAL YEAR PROJECT PRESENTATION[P2]

STUDY OF OPTICAL OFDMPRESENTED BY-

MANGI LAL [101055]

MAYANK JOSHI [101058]

MAYUR NAYAK [101059]

Introduction

• The optical transmission system design involves accounting for different effects that may degrade the signal during modulation, propagation, and detection processes. The transmission quality is assessed by the received signal-to-noise ratio (SNR), which is the ratio between signal power and noise power at the decision point.

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 of these 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 main

categories 1. Coherent detection. 2. Direct detection

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.

Usefulness of Optical OFDM

• It is used in high speed data transmission such as 4-G technology.• It exploits optical bandwidth efficiently .• It is suitable for long- haul transmission because of its

ability to deal with large pulse spreads due to chromatic dispersion.• High speed transmission over multimode optical fibers.• Improvement of the spectral efficiency .

Block Diagram of CO-OFDM

The above block diagram shows the conceptual diagram of a generic CO-OFDM system, including five basic functional blocks1: RF OFDM transmitter, RF-to-optical (RTO) up-converter, optical link, optical-to-RF (OTR) down-converter, and RF OFDM receiver.

• The function of the OFDM transmitter is to map the data bits into each OFDM symbol, and generate the time series by inverse discrete Fourier transform including insertion of the guard interval, and then upconvert to an appropriate RF frequency to be fed into an optical upconverter.

• The function of the optical upconverter is to linearly shift the OFDM spectrum from the RF domain to the optical domain.

Mathematical Formulation

The OFDM baseband signal s(t) is represented by the above equation where is the information symbol at the subcarrier, f (t) is the pulse waveform of the symbol, is the frequency of the subcarrier, and ∆f is the subcarrier spacing, , and are the OFDM symbol period, guard interval length and observation period, respectively.

𝑠 (𝑡 )= ∑𝑖=−∞

∞

∑𝑘=1

𝑁 𝑠𝑐

𝑐𝑘𝑖exp ( 𝑗 2𝜋 𝑓 𝑘 ( 𝑡−𝑖𝑇 𝑠 ) ) 𝑓 (𝑡−𝑖𝑇 𝑠)

,

The field at the output of the optical upconverter is given by

Where

The received optical signal after traversing through total chromatic dispersion of Dt, can be approximated as

)) where The signal then passes through an optical downconverter, which consists of a pair of balanced photodetectors. It is very critical to use an OBPF before the photodetectors to eliminate interference and optical noise.

𝐸𝑠=𝑒𝑗 {2𝜋 ( 𝑓 𝐿𝐷1+ 𝑓 𝐿𝑂1 ) 𝑡+∅𝐿𝐷 1} .∑

𝑘=1

𝑁𝑠𝑐

𝑐𝑘𝑒𝑗 2𝜋 𝑓 𝑘𝑡

Design Progress• In the present research the programming of the OFDM

coder and decoder has been done with MATLAB software. • These binary data values are mapped to symbols, using

QPSK or one of the 16 QAM techniques. • Performance monitoring is very important feature for

optical systems. Though there exists number of criteria for monitoring performance of optical transmission systems. • Performance of channel could be directly determined by

the BER, which is depending upon OSNR, dispersion and non linear effects. OSNR is very important and dominant performance parameter.

Simulation Results

• This section is reporting simulation results for various parameters of optical OFDM system.

The cause of occurrence of chromatic dispersion is difference in group velocities among the different spectral components. The above graph shows chromatic dispersion which has been analyzed with reference to wavelength.

Conclusions• Modelling and comprehensive analysis of optical OFDM

transmission has been carried out in the project. The main conclusions drawn are that the BER value of the QAM modulator is better than QPSK modulator.

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.

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 optical

orthogonal frequency division multiplexing” ELECTRONICS LETTERS 11th May 2006 Vol. 42 No. 10• William Shieh and Ivan Djordjevic “OFDM for Optical

Communications”.• Harsimran Jit Kaur, Maninder Lal Singh Optics and

Photonics Journal, 2013, Modelling and Reporting Parameters of Optical OFDM System Using Different Modulation Techniques.