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Title: Study on Advanced Modulation Formats in Coherent Optical Communication Systems
Keywords: Coherent Optical Communications, Advanced Modulation Formats, Laser Phase Noise, Phase Estimation
Issue Date: 23-Aug-2012
Citation: ZHANG HONGYU (2012-08-23). Study on Advanced Modulation Formats in Coherent Optical Communication Systems. ScholarBank@NUS Repository.
Abstract: This thesis systemically studies the performance of different advanced modulation formats (4-point, 8-point, and higher-order) in the presence of laser phase noise and additive white Gaussian noise (AWGN), and experimentally verifies our analysis and simulations in the coherent optical B2B systems. First of all, the conditional bit-error rates (BER) of different modulation formats are derived in the presence of a random phase estimation error and AWGN. Through a series of approximations, simple and accurate approximate BERs are obtained, which allow quick estimations of the BER performance and laser linewidth (LLW) tolerance. In addition, these approximate BERs can also lead to some initial results as follows: (1) The cross-over signal-to-noise ratio (SNR) algorithm between QPSK and (1, 3), which allows a quick and accurate estimation of the cross-over SNR point between QPSK and (1, 3) under different phase estimation error variance; (2) The ring ratio optimization algorithms of 8-star QAM and rotated 8-star QAM, respectively. These algorithms can be used to quickly find out the optimum ring ratio under different conditions, such as SNR/bit, LLW, and symbol rate; (3) The reason why 8-star QAM has more phase noise tolerance than rotated 8-star QAM is discussed based on the approximate BERs. We also evaluate the BER performance and LLW tolerance for higher-order modulation formats, such as 16-star QAM and 64-QAM. The optimum ring ratio and ring ratio fluctuation penalty is numerically studied for 16-star QAM. Moreover, coherent optical B2B experiments are conducted in this thesis to verify our analysis and simulations. This study illustrates the procedure in detail how to carry out the analysis for advanced modulation formats, and how to optimize the performance for two-dimensional constellations. More importantly, the results in the thesis provide algorithms and comments which can be used for the electrical engineers to choose the best modulation formats and optimum parameters of each constellation under different conditions.
Appears in Collections:Ph.D Theses (Open)

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