  The performance of long-haul high speed coherent optical fiber communication
systems is significantly degraded by the laser phase noise and the equalization
enhanced phase noise (EEPN). In this paper, the analysis of the one-tap
normalized least-mean-square (LMS) carrier phase recovery (CPR) is carried out
and the close-form expression is investigated for quadrature phase shift keying
(QPSK) coherent optical fiber communication systems, in compensating both laser
phase noise and equalization enhanced phase noise. Numerical simulations have
also been implemented to verify the theoretical analysis. It is found that the
one-tap normalized least-mean-square algorithm gives the same analytical
expression for predicting CPR bit-error-rate (BER) floors as the traditional
differential carrier phase recovery, when both the laser phase noise and the
equalization enhanced phase noise are taken into account.
