PAM-6 Coded Modulation for IM/DD Channels with a Peak-Power Constraint

TL;DR

This paper explores probabilistic amplitude shaping with PAM-6 modulation for IM/DD channels under peak-power constraints, demonstrating improved performance over traditional PAM-8 and QAM-32 schemes.

Contribution

It introduces a PAS-based PAM-6 modulation scheme optimized for peak-power constrained IM/DD channels, showing significant performance gains over existing modulation formats.

Findings

PAM-6 with PAS outperforms PAM-8 at rates up to 2.3 bits per channel use.

PAM-6 with PAS outperforms QAM-32 by up to 1 dB with soft decoding.

A framed cross-shaped QAM-32 scheme achieves similar gains.

Abstract

Coded modulation with probabilistic amplitude shaping (PAS) is considered for intensity modulation/direct detection channels with a transmitter peak-power constraint. PAS is used to map bits to a uniform PAM-6 distribution and outperforms PAM-8 for rates up to around 2.3 bits per channel use. PAM-6 with PAS also outperforms a cross-shaped QAM-32 constellation by up to 1 dB and 0.65 dB after bit-metric soft- and hard decoding, respectively. An alternative PAM-6 scheme based on a framed cross-shaped QAM-32 constellation is proposed that shows similar gains.