To achieve reliable and efficient transmissions in free-space optical (FSO) communication, this paper designs a new protograph low-density parity-check (PLDPC) coded generalized spatial multipulse position modulation (GSMPPM) system over weak turbulence channels. Specifically, we investigate the PLDPC code, generalized space shift keying (GSSK) modulation, and MPPM constellation. First, we propose a type of novel GSMPPM constellations that intelligently integrates the GSSK into MPPM, referred to as asymmetric dual-mode (ADM) constellations, so as to improve the performance of the PLDPC-coded GSMPPM system. Furthermore, exploiting a protograph extrinsic information transfer (PEXIT) algorithm, we construct a type of improved PLDPC code, referred to as I-PLDPC code, which outperforms the existing PLDPC codes over weak turbulence channels. Analytical and simulation results show that the proposed ADM constellations and the proposed I-PLDPC code can obtain noticeable performance gains over their counterparts. Therefore, the proposed PLDPC-coded GSMPPM system with ADM constellations is competent to satisfy the high-reliability requirement for FSO applications.

翻译：为了实现自由空间光通信中的可靠高效传输，本文针对弱湍流信道设计了一种新型原型图低密度奇偶校验（PLDPC）码编码的广义空间多脉冲位置调制（GSMPPM）系统。具体而言，我们研究了PLDPC码、广义空间移位键控（GSSK）调制以及MPPM星座。首先，我们提出了一类新型GSMPPM星座，该星座将GSSK智能集成到MPPM中，称为非对称双模（ADM）星座，从而提升PLDPC编码GSMPPM系统的性能。此外，利用原型图外信息转移（PEXIT）算法，我们构建了一种改进型PLDPC码（记为I-PLDPC码），其在弱湍流信道中性能优于现有PLDPC码。分析与仿真结果表明，所提出的ADM星座与I-PLDPC码相比同类方案可取得显著性能增益。因此，采用ADM星座的PLDPC编码GSMPPM系统能够满足FSO应用的高可靠性需求。