  Using coherent optical detection and digital signal processing, laser phase
noise and equalization enhanced phase noise can be effectively mitigated using
the feed-forward and feed-back carrier phase recovery approaches. In this
paper, theoretical analyses of feed-back and feed-forward carrier phase
recovery methods have been carried out in the long-haul high-speed n-level
phase shift keying (n-PSK) optical fiber communication systems, involving a
one-tap normalized least-mean-square (LMS) algorithm, a block-wise average
algorithm, and a Viterbi-Viterbi algorithm. The analytical expressions for
evaluating the estimated carrier phase and for predicting the bit-error-rate
(BER) performance (such as the BER floors) have been presented and discussed in
the n-PSK coherent optical transmission systems by considering both the laser
phase noise and the equalization enhanced phase noise. The results indicate
that the Viterbi-Viterbi carrier phase recovery algorithm outperforms the
one-tap normalized LMS and the block-wise average algorithms for small phase
noise variance (or effective phase noise variance), while the one-tap
normalized LMS algorithm shows a better performance than the other two
algorithms for large phase noise variance (or effective phase noise variance).
In addition, the one-tap normalized LMS algorithm is more sensitive to the
level of modulation formats.
