Efficient Phase Noise Mitigation For Coherent Optical OFDM

Coherent optical orthogonal frequency division multiplexing(CO-OFDM) is a promising candidate for high-speed long-haul optical communications due to its high chromatic dispersion(CD) and polarization mode dispersion(PMD) tolerance. But the coherent system performance suffer seriously from laser phase noise, because it introduces both common phase error(CPE) and inter-carrier interference(ICI), which are the focus of research in CO-OFDM system.In this paper, the phase noise and its mitigation algorithms for CO-OFDM system are studied, especially the algorithms aim to reduce CPE and ICI. Several Novel algorithms have been implemented and analyzed through simulation, and new improved algorithms are proposed. The main contents and results of this research are as follows:1) The application background, technical advantages and research status of CO-OFDM communication system is briefly introduced in this paper. The related technical principles are also expounded, especially the professional knowledge used in the research.2) A CO-CFDM communication simulation system has been built by a software called Opti System, combined with Matlab modules. Several related algorithms have been implemented and analyzed for further research, their advantages and disadvantages are shown by numerous chart and analysis.3) We proposed a novel iteration-free blind phase noise estimation for CO-OFDM communication system. The new cost function is derived under some assumptions, where it is infinitely approximated by the sine and cosine functions. By means of the analytical formula of the cost function, the initial coarse common phase error can be obtained with only some samples, where the algorithm avoids computational complexity of conventional blind phase noise compensation scheme. It is proved by the simulation results that the phase noise can be effectively compensated with the proposed blind estimation method.4) We proposed a decision-aided mitigation with time-domain average approximation for CO-OFDM. The ICI mitigation scheme is performed through the combination of frequencydomain symbol decision-aided estimation and the ICI phase noise time-average approximation. An additional initial decision process with suitable threshold is introduced so that only the decision data with high correct rate may be used to suppress the data error. Our proposed ICI mitigation scheme is proved to be effective in removing the ICI for a simulated CO-OFDM with 16-QAM modulation format. With the slightly high computational complexity, it outperforms the similar time-domain blind ICI(Avg-BL-ICI) algorithm at a relatively wide laser line-width and high OSNR.