The inherent limitations in scaling up ground infrastructure for future wireless networks, combined with decreasing operational costs of aerial and space networks, are driving considerable research interest in multisegment ground-air-space (GAS) networks. In GAS networks, where ground and aerial users share network resources, ubiquitous and accurate user localization becomes indispensable, not only as an end-user service but also as an enabler for location-aware communications. This breaks the convention of having localization as a byproduct in networks primarily designed for communications. To address these imperative localization needs, the design and utilization of ground, aerial, and space anchors require thorough investigation. In this tutorial, we provide an in-depth systemic analysis of the radio localization problem in GAS networks, considering ground and aerial users as targets to be localized. Starting from a survey of the most relevant works, we then define the key characteristics of anchors and targets in GAS networks. Subsequently, we detail localization fundamentals in GAS networks, considering 3D positions and orientations. Afterward, we thoroughly analyze radio localization systems in GAS networks, detailing the system model, design aspects, and considerations for each of the three GAS anchors. Preliminary results are presented to provide a quantifiable perspective on key design aspects in GAS-based localization scenarios. We then identify the vital roles 6G enablers are expected to play in radio localization in GAS networks.

翻译：未来无线网络中地面基础设施扩展的固有局限性，加之空中与空间网络运营成本的持续降低，正推动多段式空地-空间（GAS）网络研究的热潮。在GAS网络中，地面与空中用户共享网络资源，普适且精准的用户定位已成为不可或缺的技术需求——不仅作为终端用户服务，更是实现位置感知通信的关键支撑。这打破了传统通信网络将定位作为副产品的惯例。为满足这些迫切的定位需求，需深入探究地面、空中与空间锚点的设计与应用。本教程系统分析GAS网络中的无线电定位问题，将地面与空中用户作为待定位目标，从相关研究综述切入，定义GAS网络中锚点与目标的关键特征。随后，考虑三维位置与朝向，详述GAS网络定位基础原理。在此基础上，深入分析GAS网络中的无线电定位系统，系统阐述系统模型、设计考量及三类GAS锚点的特性，并通过初步实验给出量化视角的关键设计要素。最后，本文识别了6G关键技术将在GAS网络无线电定位中发挥的重要作用。