Optical wireless communication (OWC) has garnered significant importance to provide gigabit capacity links owing to its unique features. Free-space optics (FSO) communication, which is the term used for OWC in an outdoor scenario, is a good candidate to establish ground-to-satellite/satellite-to-ground links. Despite of many advantages, FSO communication in uplink is limited by the adverse effects of beam-wander, beam scintillation, and pointing errors. Therefore, to counteract the limitations, it is wise to backup FSO links with reliable radio frequency (RF) links. In addition, the complementary characteristics exhibited by FSO and RF links to atmospheric effects have paved the way for hybrid FSO/RF communication. In recent years, a growing interest is also witnessed in the research and development of space–air–ground integrated network (SAGIN). This article aims to fuse FSO and RF technologies for integrated space–air–ground uplink networks utilizing unmanned aerial vehicle (UAV), such as high-altitude platform station (HAPS) as a relay station for achieving better reliability. Thus, we propose single-hop and SAGIN-based dual-hop system models for uplink satellite communication with hybrid FSO/RF links and the performance is investigated using analytical and simulation results. In summary, the results show that hybrid FSO/RF systems perform better than the FSO systems in an uplink scenario due to the backup RF link.

中文翻译：

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具有混合 FSO/RF 通信的基于 HAPS 的天-空-地综合网络中继：性能分析

由于其独特的功能，光无线通信 (OWC) 在提供千兆容量链路方面具有重要意义。自由空间光学 (FSO) 通信是室外场景中 OWC 的术语，是建立地对卫星/卫星对地链路的良好候选者。尽管有许多优点，但上行链路中的 FSO 通信受到波束漂移、波束闪烁和指向错误的不利影响。因此，为了抵消这些限制，明智的做法是使用可靠的射频 (RF) 链路备份 FSO 链路。此外，FSO 和 RF 链路对大气效应的互补特性为混合 FSO/RF 通信铺平了道路。近年来，空-空-地一体化网络（SAGIN）的研究和开发也越来越受到关注。本文旨在融合 FSO 和 RF 技术，以利用无人机 (UAV)，如高空平台站 (HAPS) 作为中继站，以实现更高的可靠性，以构建天-空-地一体化上行链路网络。因此，我们为具有混合 FSO/RF 链路的上行链路卫星通信提出了单跳和基于 SAGIN 的双跳系统模型，并使用分析和仿真结果研究了性能。总之，结果表明，由于备份 RF 链路，混合 FSO/RF 系统在上行链路场景中的性能优于 FSO 系统。我们为具有混合 FSO/RF 链路的上行链路卫星通信提出了单跳和基于 SAGIN 的双跳系统模型，并使用分析和仿真结果研究了性能。总之，结果表明，由于备份 RF 链路，混合 FSO/RF 系统在上行链路场景中的性能优于 FSO 系统。我们为具有混合 FSO/RF 链路的上行链路卫星通信提出了单跳和基于 SAGIN 的双跳系统模型，并使用分析和仿真结果研究了性能。总之，结果表明，由于备份 RF 链路，混合 FSO/RF 系统在上行链路场景中的性能优于 FSO 系统。