Abstract
We present a low-complexity carrier estimator with an effective filter length that automatically adapts
according to the signal-to-noise ratio, laser-linewidth-symbol-duration product, nonlinear phase noise, and modulation
format. Laser-linewidth and frequency-offset tolerances are studied. The filter length of a carrier estimator is shown
to affect the cycle slip probability besides the bit-error rate (BER) performance. Considering that
forward-error-correction codes are not robust to burst errors and phase slips, we demonstrate that filter-length
optimization is necessary to avoid spectral-efficiency reduction in pilot assisted systems and potential system
failures in differential encoding systems. Our estimator achieves a lower cycle slip probability and a greater
nonlinear phase noise tolerance than DiffFE-MPE, DiffFE-BPS, and complex-weighted decision-aided maximum-likelihood
(CW-DA-ML) estimator. DiffFE-MPE and DiffFE-BPS refer to the differential frequency estimator (DiffFE) followed by
block
$M{th}$
power phase estimator (MPE) and blind phase
search (BPS), respectively. For a 4100 km quaternary phase-shift keying transmission at a BER of
${2.5} \times {10}^{ - 2}$
, our estimator achieves a cycle
slip probability of
${2.9} \times {10}^{ - 7}$
compared
to
${5.6} \times {10}^{ - 6}, {5.3} \times {10}^{ - 6} $
, and
${3.2} \times {10}^{ - 7} $
for
DiffFE-MPE, DiffFE-BPS, and CW-DA-ML, respectively.
© 2013 IEEE
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