The sixth-generation wireless networks are envisioned to deliver ubiquitous, seamless, and intelligent connectivity that reaches far beyond the limits of terrestrial infrastructure. Non-terrestrial networks (NTNs) are central to this vision, extending coverage to underserved regions, remote terrain, and disaster zones that terrestrial deployment cannot economically reach. However, NTN architecture faces numerous limitations: severe path loss over long distances, long propagation delays, large and time-varying Doppler shifts, limited visibility windows, and tight on-board energy and computing budgets. Semantic communication (SemCom), which conveys the meaning of data rather than its raw bit-level representation, is unusually well matched to these conditions: extreme compression rate for task-oriented eases bandwidth scarcity, deep joint source-channel coding prevents the cliff effect due to low signal-to-noise ratio, and generative-AI reconstructs content from sparse cues that survive rain-faded or blocked links. This observation, that each NTN limitation maps onto a SemCom property that addresses it, motivates our survey. We first walk through the NTN limitations one by one, pairing each with the SemCom design choices that complement it, then we organize the literature along three axes: the NTN platform, the semantic methodology, and the supporting techniques, and follow this with platform-by-platform deep dives on satellite-centric, UAV/HAPS-centric, and integrated SAGIN systems. The survey concludes by identifying open research problems, gaps in existing standards, and future directions, including the application of foundation models, energy-aware scheduling, and quantum-assisted SemCom for deep space communication.

翻译：第六代无线网络被设想为能够提供超越地面基础设施限制的泛在、无缝且智能的连通性。非地面网络（NTN）是实现这一愿景的核心，它将覆盖范围扩展至地面部署无法经济到达的欠发达地区、偏远地形及灾区。然而，NTN架构面临诸多限制：长距离下的严重路径损耗、长传播时延、大且时变的多普勒频移、有限的可视窗口，以及严格的星载能量与计算预算。语义通信（SemCom）传递的是数据的含义而非其原始比特级表示，与这些条件异常契合：面向任务的极端压缩率缓解了带宽稀缺性；深度联合源信道编码避免了低信噪比下的悬崖效应；生成式AI则能从经受雨衰或链路遮挡的稀疏线索中重建内容。这种观察——即每个NTN限制都映射至一个可应对该限制的SemCom特性——构成了本综述的动机。我们首先逐一审视NTN的限制，并将每个限制与互补的SemCom设计选择配对；随后沿三个维度组织文献：NTN平台、语义方法及支撑技术；接着针对以卫星为中心、以无人机/高空平台为中心及综合空天地一体化网络系统，逐一进行平台层面的深入剖析。本综述最后指出了开放的研究问题、现有标准的空白及未来方向，包括基础模型的应用、能量感知调度，以及面向深空通信的量子辅助语义通信。