Channel equalization using independent component analysis in PDM-CO-OFDM

We propose a channel equalization method without training symbols (TSs) based on the independent component analysis (ICA) for polarization-division- multiplexing coherent-optical orthogonal-frequency-division-multiplexing (PDM-CO-OFDM) transmission systems. Compared with the conventional TS-based channel equalization method, the proposed method with 80 collected OFDM symbols shows a better transmission performance in the case of QPSK modulation format, and almost the same performance in the case of 16-quadrature amplitude modulation (QAM) format. In addition, we propose a new channel frequency response initialization method to solve the permutation indeterminacy and complex uncertain scaling problems in ICA-based channel equalization. The proposed initialization method shows faster convergence speed than the conventional random initialization method in the channel equalization process. Finally, we examine the number of OFDM symbols required for the proposed ICA-based channel equalization. This study shows that 40 and 80 OFDM symbols are sufficient for the QPSK and 16-QAM formats, respectively. Since the proposed ICA-based channel equalization method is free of TSs, the spectral efficiency of the PDM-CO-OFDM systems can be improved considerably.