Free space optical (FSO) communication systems provide wireless line of sight connectivity in the unlicensed spectrum, and wireless optical communication achieves higher data rates compared to their radio frequency (RF) counterparts. FSO systems are particularly attractive for last mile access problem by bridging fiber optic backbone connectivity to RF access networks. To cope with this practical deployment scenario, there has been increasing attention to the so-called dual-hop (RF/FSO) systems where RF transmission is used at a hop followed by FSO transmission to another. In this article, we study the performance of cooperative transmission systems using a mixed RF-FSO DF (decode and forward) relay using error-correcting codes including QC-LDPC codes at the relay level. The FSO link is modeled by the gamma-gamma distribution, and the RF link is modeled by the Additive White Gaussian Noise (AWGN) model. Another innovation in this article is the use of cooperative systems using a mixed FSO/RF DF relay using quasicyclic low-density parity check (QC-LDPC) codes at the relay level. We also use the space-coupled low-density parity check (SC-LDPC) codes on the same scheme to show its importance in cooperative optical transmission but also in hybrid RF/FSO transmission. The latter will be compared with QC-LDPC codes. The use of mixed RF/FSO cooperative transmission systems can improve the reliability and transmission of information in networks. The results demonstrate an improvement in the performance of the cooperative RF/FSO DF system based on QC-LDPC and SC-LDPC codes compared to RF/FSO systems without the use of codes, but also to the DF systems proposed in the existing literature.

中文翻译：

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基于准循环LDPC码和空间耦合LDPC码的混合RF / FSO协作系统的性能

自由空间光（FSO）通信系统在未许可的频谱中提供了无线视线连接，并且与之相比，无线光通信可实现更高的数据速率。FSO系统通过将光纤骨干网连接性连接到RF接入网络，特别适合最后一英里的接入问题。为了应对这种实际的部署方案，人们越来越关注所谓的双跳（RF / FSO）系统，其中在一个跳上使用RF传输，然后再将FSO传输到另一个跳。在本文中，我们研究在中继级使用混合纠错码（包括QC-LDPC码）的混合RF-FSO DF（解码和转发）中继的协作传输系统的性能。FSO链接由gamma-gamma分布建模，RF链路由加性高斯白噪声（AWGN）模型建模。本文的另一项创新是使用在混合系统中使用混合FSO / RF DF中继的系统，并在中继级使用准循环低密度奇偶校验（QC-LDPC）代码。我们还对同一方案使用了空间耦合的低密度奇偶校验（SC-LDPC）码，以显示其在协作光传输中以及在混合RF / FSO传输中的重要性。后者将与QC-LDPC码进行比较。混合使用RF / FSO协作传输系统可以提高网络中信息的可靠性和传输。结果表明，与不使用代码的RF / FSO系统相比，基于QC-LDPC和SC-LDPC代码的协作RF / FSO DF系统的性能有了改善，