  Probabilistic constellation shaping (PCS) offers a significant performance
improvement over uniform signaling. It was recently discovered that long blocks
are not required to achieve maximum shaping gain when transmitting over the
nonlinear fiber channel because short-length PCS effectively mitigates fiber
nonlinear interference (NLI). The reason for this behavior is that short-length
PCS implicitly induces some temporal properties in the shaped transmit sequence
that are beneficial for the fiber-optic channel. To achieve robust data-aided
digital signal processing of high-order QAM, periodic quaternary phase shift
keying pilots are typically inserted into the high-order QAM transmit sequence.
In this work, we investigate in simulations the effect of such pilot-aided
signaling on NLI mitigation. Albeit modifying the temporal properties of the
shaped transmit sequence, a pilot rate of 1/32 is found to not alter the
beneficial effects of short-length PCS. The operation meaning of this finding
is that even with pilot-aided signaling, long PCS block lengths are not
required for maximum shaping gain.
