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Article
Spectral Efficiency Improvement of the Optical Communication Systems

Authors: Aqeel R. Farhan --- Dr. Ali Y. Fattah
Journal: IRAQI JOURNAL OF COMPUTERS,COMMUNICATION AND CONTROL & SYSTEMS ENGINEERING المجلة العراقية لهندسة الحاسبات والاتصالات والسيطرة والنظم ISSN: 18119212 Year: 2014 Volume: 14 Issue: 1 Pages: 44-57
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

Abstract –In this paper, different amplitude and phase modulation formats are investigated and compared to find the optimum one among them for high spectral efficiency (SE) Wavelength Division Multiplexing (WDM) systems with an acceptable value of the Bit Error Rate (BER). Also, the effectiveness of using the polarization interleaving scheme in minimizing the nonlinear effects in the optical fiber channel for the various modulation formats is investigated. (Optisystem v 7.0) A simulation package is used to simulate the system. The simulation results show the effectiveness of using the polarization interleaving in decreasing the nonlinear effects. RZ modulation formats are found to give a better BER value than the corresponding NRZ formats but with a smaller value of the SE. Among the compared modulation formats, RZ-AMI and the RZ-DQPSK are the only formats that are found to give the optimal performance for high capacity WDM networks.


Article
Electronic Signal Processing for Cancelation of Optical Systems Impairments

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Abstract

Abstract –In this paper 40 Gb/s DP-QPSK system with coherent reception and DSPunit for optical fiber impairments compensation is proposed . The DSP unit processesthe detected coherent DP-QPSK signal. The Chromatic Dispersion (CD) is compensatedusing a simple transversal digital filter and Polarization Mode Dispersion (PMD) iscompensated using adaptive butterfly equalizer which is realized by applying theconstant-modulus algorithm (CMA). A nonlinear compensator (NLC) is used forcompensating the nonlinear effects based on the technique of multi-span backpropagation.A modified Viterbi-and-Viterbi phase estimation algorithm (workingjointly on both polarizations) is then used to compensate for phase and frequencymismatch between the transmitter and local oscillator (LO). After the digital signalprocessing is complete, the signal is sent to the detector and decoder, and then to theBER test set for direct-error-counting. The presented system is designed and simulatedusing OptiSystem (2011) software interfaced with MATLAB software R2011a forimplementing the DSP unit algorithms. The performance of each part of the system isanalyzed by showing the optical spectrum, RF spectrum, electrical constellationdiagrams, eye diagram and BER performance for different sampling rates and differentbit rates.

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