  The performance of long-haul coherent optical fiber transmission system is
significantly affected by the equalization enhanced phase noise (EEPN), due to
the interaction between the electronic dispersion compensation (EDC) and the
laser phase noise. In this paper, we present a comprehensive study on different
chromatic dispersion (CD) compensation and carrier phase recovery (CPR)
approaches, in the n-level phase shift keying (n-PSK) and the n-level
quadrature amplitude modulation (n-QAM) coherent optical transmission systems,
considering the impacts of EEPN. Four CD compensation methods are considered:
the time-domain equalization (TDE), the frequency-domain equalization (FDE),
the least mean square (LMS) adaptive equalization are applied for EDC, and the
dispersion compensating fiber (DCF) is employed for optical dispersion
compensation (ODC). Meanwhile, three carrier phase recovery methods are also
involved: a one-tap normalized least mean square (NLMS) algorithm, a block-wise
average (BWA) algorithm, and a Viterbi-Viterbi (VV) algorithm. Numerical
simulations have been carried out in a 28-Gbaud dual-polarization quadrature
phase shift keying (DP-QPSK) coherent transmission system, and the results
indicate that the origin of EEPN depends on the choice of chromatic dispersion
compensation methods, and the effects of EEPN also behave moderately different
in accordance to different carrier phase recovery scenarios.
