Abstract
Next-generation optical fiber systems will employ coherent detection to
improve power and spectral efficiency, and to facilitate flexible impairment
compensation using digital signal processors (DSPs). In a fully digital
coherent system, the electric fields at the input and the output of the
channel are available to DSPs at the transmitter and the receiver, enabling
the use of arbitrary impairment precompensation and postcompensation
algorithms. Linear time-invariant (LTI) impairments such as chromatic
dispersion and polarization-mode dispersion can be compensated by adaptive
linear equalizers. Non-LTI impairments, such as laser phase noise and Kerr
nonlinearity, can be compensated by channel inversion. All existing
impairment compensation techniques ultimately approximate channel inversion
for a subset of the channel effects. We provide a unified multiblock
nonlinear model for the joint compensation of the impairments in fiber
transmission. We show that commonly used techniques for overcoming different
impairments, despite their different appearance, are often based on the same
principles such as feedback and feedforward control, and
time-versus-frequency-domain representations. We highlight equivalences
between techniques, and show that the choice of algorithm depends on making
tradeoffs.
© 2010 IEEE
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