Precipitated by the technological innovations in near-space platform stations (NSPSs), the near-space communication (NS-COM) network has emerged as an indispensable part of the next-generation space-air-ground integrated network (SAGIN) that facilitates ubiquitous coverage and broadband data transfer. This article aims to provide a comprehensive overview of NS-COM. First, we investigate the differences between NS-COM and the existing terrestrial cellular networks as well as satellite-based and unmanned-aerial-vehicle (UAV)-based communication networks, which is followed by a review of NS-COM development. Then we explore the unique characteristics of NS-COM regarding the platforms and the propagation environment of near space. The main issues of NS-COM are identified, resulting from the extremely long transmission distance, limitations of the communication payloads on NSPS, and the complex atmospheric constitution of near space. Then various application scenarios of NS-COM are discussed, where the special technical requirements are also revealed, from physical-layer aspects like transceiver design to upper-layer aspects like computational offloading and NSPS placement. Furthermore, we investigate the coexistence of NS-COM and ground networks by treating each other as interferers or collaborators. Finally, we list several potential technologies for NS-COM from the perspective of spectrum usage, and highlight their technical challenges for future research.

中文翻译：

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近空通信：天空地一体化网络的新机制

受近空平台站（NSPS）技术创新的推动，近空通信（NS-COM）网络已成为下一代空天地综合网络（SAGIN）不可或缺的一部分，可促进无处不在的通信覆盖和宽带数据传输。本文旨在全面概述 NS-COM。首先，我们研究了 NS-COM 与现有地面蜂窝网络以及基于卫星和无人机 (UAV) 的通信网络之间的差异，然后回顾了 NS-COM 的发展。然后我们探讨了NS-COM在临近空间平台和传播环境方面的独特特征。确定了 NS-COM 的主要问题，由于传输距离极长，NSPS 上通信有效载荷的局限性，以及临近空间复杂的大气结构。然后讨论了NS-COM的各种应用场景，其中还揭示了特殊的技术要求，从收发器设计等物理层方面到计算卸载和NSPS放置等上层方面。此外，我们通过将彼此视为干扰者或合作者来调查 NS-COM 和地面网络的共存。最后，我们从频谱使用的角度列出了 NS-COM 的几种潜在技术，并强调了它们对未来研究的技术挑战。从收发器设计等物理层方面到计算卸载和 NSPS 放置等上层方面。此外，我们通过将彼此视为干扰者或合作者来调查 NS-COM 和地面网络的共存。最后，我们从频谱使用的角度列出了 NS-COM 的几种潜在技术，并强调了它们对未来研究的技术挑战。从收发器设计等物理层方面到计算卸载和 NSPS 放置等上层方面。此外，我们通过将彼此视为干扰者或合作者来调查 NS-COM 和地面网络的共存。最后，我们从频谱使用的角度列出了 NS-COM 的几种潜在技术，并强调了它们对未来研究的技术挑战。