The quest for ubiquitous mobile coverage has catalyzed two fundamentally distinct architectural paradigms: Direct-to-Cell (D2C) and standardized 3GPP Non-Terrestrial Networks (NTN). D2C, pioneered by SpaceX Starlink and AST SpaceMobile, leverages existing terrestrial spectrum and unmodified consumer handsets to provide emergency connectivity as a market-driven overlay. In contrast, 3GPP NTN, standardized across Releases 17-19, offers a systematic satellite-native framework designed for long-term scalability, high-throughput broadband, and deep integration with terrestrial 5G/6G networks. This paper presents a comprehensive technical comparison of these approaches, analyzing their standardization trajectories, network architectures, physical-layer innovations, security postures, and operational trade-offs. We further examine their implications for emerging 6G use cases, particularly autonomous driving, where safety-critical redundancy motivates a hybrid tri-link architecture combining terrestrial 5G, NTN broadband, and D2C emergency fallback. Our analysis shows that, although D2C enables rapid market entry through legacy-device compatibility, NTN provides superior performance, security, and scalability, positioning it as the foundational framework for 6G satellite-terrestrial convergence. A hybrid model that combines the strengths of both paradigms is identified as the most practical path toward truly global connectivity.

翻译：实现无处不在的移动覆盖需求催生了两种本质不同的架构范式：直连手机（D2C）与标准化3GPP非地面网络（NTN）。由SpaceX星链和AST SpaceMobile率先提出的D2C技术，利用现有地面频谱和未经修改的消费级手机，以市场驱动的覆盖扩展形式提供应急连接。相比之下，3GPP NTN在Release 17-19中完成标准化，提供了专为长期可扩展性、高吞吐量宽带以及与地面5G/6G网络深度融合而设计的系统性卫星原生框架。本文对这两种方法进行全面技术对比，分析其标准化演进路线、网络架构、物理层创新、安全态势及运营权衡。我们进一步考察了它们对新兴6G应用场景的影响，特别是自动驾驶领域——其中安全关键冗余催生了融合地面5G、NTN宽带和D2C应急回退的混合三链路架构。分析表明，尽管D2C通过兼容现有终端实现快速市场进入，但NTN在性能、安全性和可扩展性方面具有更优表现，使其成为6G星地融合的基础框架。结合两种范式优势的混合模型被视为实现真正全球连接的最切实路径。