Cellular communication standards have been established to ensure connectivity across most urban environments, complemented by deployment hardware and facilities tailored for city life. At the same time, numerous initiatives seek to broaden connectivity to rural and developing areas. However, with nearly half the global population still offline, there is an urgent need to drive research toward enhancing connectivity in areas and conditions that deviate from the norm. This article delves into innovative communication solutions not only for hard-to-reach and extreme environments but also introduces “hard-to-serve” areas as a crucial, yet underexplored, category within the broader spectrum of connectivity challenges. We explore the latest advancements in communication systems designed for environments subject to extreme temperatures, harsh weather, excessive dust, or even disasters such as fires. Our exploration spans the entire communication stack, covering communications on isolated islands, sparsely populated regions, mountainous terrains, and even underwater and underground settings. We highlight system architectures, hardware, materials, algorithms, and other pivotal technologies that promise to connect these challenging areas. Through case studies, we explore the application of 5G for innovative research, long range (LoRa) for audio messages and emails, LoRa wireless connections, free-space optics, communications in underwater and underground scenarios, delay-tolerant networks, satellite links, and the strategic use of shared spectrum and TV white space (TVWS) to improve mobile connectivity in secluded and remote regions. These studies also touch on prevalent challenges such as power outages, regulatory gaps, technological availability, and human resource constraints, where we introduce the concept of peri-urban hard-to-serve areas where populations might struggle with affordability or lack the skills for traditional connectivity solutions. This article provides an exhaustive summary of our research, showcasing how 6G and future networks will play a crucial role in delivering connectivity to areas that are hard-to-reach, hard-to-serve, or subject to extreme conditions (ECs).

中文翻译：

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探索互联系统的边界：难以到达的区域和极端条件的通信


蜂窝通信标准已经建立，以确保在大多数城市环境中的连接性，并辅以为城市生活量身定制的部署硬件和设施。与此同时，许多举措旨在扩大与农村和发展中地区的连接。然而，由于全球近一半的人口仍处于离线状态，因此迫切需要推动研究，以增强偏离常态的地区和条件的连通性。本文深入探讨了创新的通信解决方案，不仅适用于难以到达和极端环境，还介绍了“难以服务”的区域，这是更广泛的连接挑战中一个关键但未得到充分探索的类别。我们探索了通信系统的最新进展，这些系统专为承受极端温度、恶劣天气、过度灰尘甚至火灾等灾难的环境而设计。我们的探索跨越了整个通信堆栈，涵盖了孤岛、人烟稀少地区、山区地形，甚至水下和地下环境中的通信。我们重点介绍了有望连接这些具有挑战性的领域的系统架构、硬件、材料、算法和其他关键技术。通过案例研究，我们探讨了 5G 在创新研究中的应用、用于音频消息和电子邮件的远程 （LoRa）、LoRa 无线连接、自由空间光学器件、水下和地下场景中的通信、延迟容忍网络、卫星链路，以及战略性地使用共享频谱和电视空白 （TVWS） 来改善隐蔽和偏远地区的移动连接。 这些研究还涉及普遍的挑战，例如停电、监管差距、技术可用性和人力资源限制，其中我们引入了城郊难以服务区域的概念，这些地区的人们可能难以负担或缺乏传统连接解决方案的技能。本文对我们的研究进行了详尽的总结，展示了 6G 和未来网络将如何在为难以到达、难以服务或受极端条件 （EC） 影响的区域提供连接方面发挥关键作用。