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, orientations, and velocities. 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：未来无线网络地面基础设施规模化扩展的内在局限性，与空基及天基网络运营成本的持续下降相结合，正推动着对多段式地面-空中-空间（GAS）网络的广泛研究。在GAS网络中，地面与空中用户共享网络资源，无处不在且精准的用户定位变得不可或缺——这不仅作为终端用户服务，更是实现位置感知通信的关键使能技术。这打破了传统网络中定位仅作为通信附属功能的惯例。为满足这些迫切的定位需求，需对地面、空中及空间锚节点的设计与应用进行深入研究。本教程对GAS网络中的无线电定位问题进行了深入的系统性分析，将地面与空中用户视为待定位目标。首先综述了最具相关性的研究成果，继而界定了GAS网络中锚节点与目标节点的核心特征。随后详细阐述了GAS网络中的定位基础原理，涵盖三维位置、方向与速度的估计。接着系统分析了GAS网络中的无线电定位系统，分别针对三类GAS锚节点详述了系统模型、设计要素与考量要点。通过呈现初步实验结果，为基于GAS的定位场景关键设计要素提供了量化视角。最后，我们明确了6G使能技术在GAS网络无线电定位中预期发挥的关键作用。