With the blooming of Internet-of-Things (IoT), we are witnessing an explosion in the number of IoT terminals, triggering an unprecedented demand for ubiquitous wireless access globally. In this context, the emerging low-Earth-orbit satellites (LEO-SATs) have been regarded as a promising enabler to complement terrestrial wireless networks in providing ubiquitous connectivity and bridging the ever-growing digital divide in the expected next-generation wireless communications. Nevertheless, the stringent requirements posed by LEO-SATs have imposed significant challenges to the current multiple access schemes and led to an emerging paradigm shift in system design. In this article, we first provide a comprehensive overview of the state-of-the-art multiple access schemes and investigate their limitations in the context of LEO-SATs. To this end, we propose the amalgamation of the grant-free non-orthogonal multiple access (GF-NOMA) paradigm and the orthogonal time frequency space (OTFS) waveform, for simplifying the connection procedure with reduced access latency and enhanced Doppler-robustness. Critical open challenging issues and future directions are finally presented for further technical development.

中文翻译：

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免授权 NOMA-OTFS 范式：为 LEO 卫星物联网实现高效无处不在的访问

随着物联网（IoT）的蓬勃发展，我们见证了物联网终端数量的爆炸式增长，引发了对全球无处不在的无线接入的空前需求。在这种情况下，新兴的低地球轨道卫星（LEO-SAT）被认为是补充地面无线网络的有希望的推动者，可提供无处不在的连接性，并弥合预期的下一代无线通信中不断增长的数字鸿沟。然而，LEO-SAT 提出的严格要求对当前的多址接入方案提出了重大挑战，并导致系统设计出现新的范式转变。在本文中，我们首先全面概述了最先进的多址接入方案，并研究了它们在 LEO-SAT 环境中的局限性。为此，我们建议将免授权非正交多址 (GF-NOMA) 范式和正交时频空间 (OTFS) 波形合并，以简化连接过程，降低访问延迟并增强多普勒鲁棒性。最后提出了关键的开放性挑战问题和未来方向，以供进一步的技术发展。