Efficient Chromatic Dispersion Compensation and Carrier Phase Tracking for Optical Fiber FBMC/OQAM Systems

Offset quadratic-amplitude modulation (QAM) based filterbank multicarrier (FBMC/OQAM) is an attractive candidate to improve the spectral containment of optical fiber communication systems, especially when considering a sufficiently high number of subcarriers. As for other multicarrier modulations, the chromatic dispersion (CD) compensation is simplified in FBMC/OQAM systems since it is performed in the frequency domain. Unfortunately, FBMC/OQAM systems are sensitive to the laser phase noise (PN). The PN becomes difficult to mitigate when the number of subcarriers increases due to the increased symbol period. It results in intercarrier interference and intersymbol interference due to the loss of OQAM orthogonality. In this paper, we consider the use of moderate numbers of subcarriers to allow for simpler PN tracking. Consequently, more advanced CD compensation methods are required and a trade-off between CD and PN compensations needs to be studied. In this paper, the frequency sampling equalizer is used for the CD compensation, whereas an innovative adaptive maximum likelihood estimator is used for the PN compensation. A methodology is then presented to analyze this performance trade-off between CD and PN compensations, and design the desirable system parameters such as the number of subcarriers and the equalizer length. This is illustrated in the case of a terrestrial long-haul FBMC/OQAM transmission system, with 400-kHz laser linewidth and a 1000-km optical link.