Optimization of Probabilistic Constellation Shaping for Optical OFDM Systems with Clipping Distortion

TL;DR

This paper investigates how probabilistic constellation shaping affects PAPR and clipping distortion in optical OFDM systems, proposing an optimized PCS approach that enhances channel capacity under severe clipping.

Contribution

It introduces an optimization method for PCS in optical OFDM that accounts for clipping distortion, improving spectral efficiency and system performance.

Findings

Optimized PCS increases channel capacity under clipping distortion.

Proposed method outperforms conventional uniform signaling.

Efficient suboptimal solution based on projected gradient descent.

Abstract

Optical orthogonal frequency-division multiplexing (OFDM) and probabilistic constellation shaping (PCS) have emerged as powerful techniques to enhance the performance of optical wireless communications (OWC) systems. While PCS improves spectral efficiency and adaptability, we show that its integration with optical OFDM can inadvertently increase the peak-to-average power ratio (PAPR) of the signal, exacerbating clipping distortion due to signal clipping. This letter investigates the impact of PCS on the PAPR of direct current-biased optical OFDM (DCO-OFDM) waveforms and proposes an optimization of PCS that maximizes channel capacity, considering clipping distortion. The optimization problem is shown to be complex and non-convex. We thus present a suboptimal yet efficient solving approach based on projected gradient descent to solve the problem. Simulation results demonstrate the superiority of the proposed approach over the conventional uniform signaling, particularly under severe clipping distortion conditions.