The limited modulation bandwidth of the light emitting diodes (LEDs) presents a challenge in the development of practical high-data-rate visible light communication (VLC) systems. In this paper, a novel adaptive coded probabilistic shaping (PS)-based nonorthogonal multiple access (NOMA) scheme is proposed to improve spectral efficiency (SE) of VLC systems in multiuser uplink communication scenarios. The proposed scheme adapts its rate to the optical signal-to-noise ratio (OSNR) by utilizing non-uniformly distributed discrete constellation symbols and low complexity channel encoder. Furthermore, an alternate optimization algorithm is proposed to determine the optimal channel coding rate, constellation spacing, and probability mass function (PMF) of each user. The extensive numerical results show that the proposed PS-based NOMA scheme closely approaches the capacity of NOMA with fine granularity. Presented results demonstrate the effectiveness of our scheme in improving the SE of VLC systems in multiuser scenarios. For instance, our scheme exhibits substantial SE gains over existing schemes, namely, the pairwise coded modulation (PCM), geometric shaping (GS), and uniform-distribution schemes. These findings highlight the potential of our approach to significantly enhance VLC systems.

翻译：发光二极管（LED）的有限调制带宽对实用化高速率可见光通信（VLC）系统的发展构成了挑战。本文提出一种新颖的基于自适应编码概率整形（PS）的非正交多址接入（NOMA）方案，旨在提升多用户上行通信场景中VLC系统的频谱效率（SE）。该方案通过采用非均匀分布的离散星座符号与低复杂度信道编码器，根据光信噪比（OSNR）自适应调整传输速率。此外，提出一种交替优化算法以确定各用户的最优信道编码速率、星座间距及概率质量函数（PMF）。大量数值结果表明，所提基于PS的NOMA方案能以精细粒度逼近NOMA容量界。研究结果证实了本方案在多用户场景下提升VLC系统频谱效率的有效性。例如，与现有成对编码调制（PCM）、几何整形（GS）及均匀分布方案相比，本方案展现出显著的频谱效率增益。这些发现凸显了该方法在显著增强VLC系统性能方面的潜力。