Smart City Internet of Things will become a fundamental infrastructure to support massive machine-type communications between the widely deployed sensors serving big cities. Since there exists many location constraints for the existing terrestrial Internet of Things, the non-terrestrial Internet of Things sheds light on breaking these limits. Therefore, this article conducts a comprehensive survey on non-terrestrial Internet of Things technologies for Smart City, which is an important complement to terrestrial Internet of Things. We first present the application scenarios of Internet of Things and point out where the existing terrestrial Internet of Things cannot work perfectly. Two non-terrestrial Internet of Things technical proposals are then introduced, namely satellite Internet of Things and unmanned aerial vehicle Internet of Things. However, the focuses of these non-terrestrial Internet of Things are distinct, that is, the major problems of satellite and unmanned aerial vehicle Internet of Things are the high dynamic nature of channel and high maneuverability of unmanned aerial vehicles, respectively. The key technologies for satellite and unmanned aerial vehicle Internet of Things are then reviewed separately. Both physical and non-physical layer technologies are surveyed for satellite Internet of Things, and the route planning is mainly investigated for the unmanned aerial vehicle Internet of Things. Finally, we draw a conclusion and give some potential research directions of non-terrestrial Internet of Things.

中文翻译：

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智慧城市物联网非地面无线技术综述

智慧城市物联网将成为支持服务于大城市的广泛部署的传感器之间大规模机器类型通信的基础设施。由于现有的地面物联网存在许多位置限制，非地面物联网为打破这些限制提供了线索。因此，本文对智慧城市的非地面物联网技术进行了全面调研，是地面物联网的重要补充。我们首先介绍了物联网的应用场景，指出了现有的地面物联网不能完美运行的地方。接着介绍了两个非地面物联网技术方案，即卫星物联网和无人机物联网。然而，这些非地面物联网的侧重点各不相同，即卫星和无人机物联网的主要问题分别是信道的高动态性和无人机的高机动性。然后分别对卫星和无人机物联网的关键技术进行了回顾。卫星物联网研究物理层和非物理层技术，无人机物联网主要研究航线规划。最后，我们得出结论并给出了一些非地面物联网的潜在研究方向。卫星和无人机物联网的主要问题分别是信道的高动态性和无人机的高机动性。然后分别对卫星和无人机物联网的关键技术进行了回顾。卫星物联网研究物理层和非物理层技术，无人机物联网主要研究航线规划。最后，我们得出结论并给出一些非地面物联网的潜在研究方向。卫星和无人机物联网的主要问题分别是信道的高动态性和无人机的高机动性。然后分别对卫星和无人机物联网的关键技术进行了回顾。卫星物联网研究物理层和非物理层技术，无人机物联网主要研究航线规划。最后，我们得出结论并给出了一些非地面物联网的潜在研究方向。卫星物联网研究物理层和非物理层技术，无人机物联网主要研究航线规划。最后，我们得出结论并给出了一些非地面物联网的潜在研究方向。卫星物联网研究物理层和非物理层技术，无人机物联网主要研究航线规划。最后，我们得出结论并给出一些非地面物联网的潜在研究方向。