Fiber Nonlinearity Mitigation by Short-Length Probabilistic Constellation Shaping for Pilot-Aided Signaling

TL;DR

This paper demonstrates through simulations that short-length probabilistic constellation shaping effectively mitigates fiber nonlinear interference even when using pilot-aided signaling, eliminating the need for long shaping blocks for optimal performance.

Contribution

It shows that short-length PCS maintains its nonlinear mitigation benefits in pilot-aided systems, simplifying implementation without sacrificing shaping gain.

Findings

Short-length PCS effectively mitigates fiber NLI.

Pilot-aided signaling at 1/32 rate does not reduce shaping benefits.

Long PCS blocks are unnecessary for maximum gain with short-length PCS.

Abstract

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.