AI 中文总结
本综述针对非地面网络（NTN），系统回顾混合数模混合波束成形（HBF）技术，重点分析低轨卫星和无人机平台的HBF架构、设计挑战，梳理相关研究方向并展望未来。
AI 中文摘要
混合数模混合波束成形（HBF）已成为非地面网络（NTN）的关键使能技术，在该网络中需要大型天线阵列来补偿严重的传播损耗，但由于射频（RF）链的成本、功耗和有效载荷限制，全数字波束成形往往不切实际。与地面网络相比，低轨（LEO）卫星和无人机（UAV）等NTN平台带来了独特的HBF设计挑战，包括高移动性、多普勒效应、以视距为主的稀疏信道、严格的机载能量预算，以及对于无人机而言，波束成形与可控平台位置或轨迹之间的额外耦合。本综述对NTN系统的HBF技术进行了系统性回顾，重点关注LEO卫星和无人机通信。我们首先介绍了常见的HBF架构、信号模型、信道表示、模拟和数字预编码器设计，以及学习辅助方法，这些构成了现有研究的共同技术基础。随后，我们在五个共同类别下对两种平台进行了综述，涵盖系统架构与预编码设计、时变波束管理、网络级协作与调度、感知能力与可重构表面，以及安全性与多址接入。它们的平台特定内容在第二类差异最为显著，因为主导的时变机制在LEO有效载荷上是流量驱动的波束跳变，而在无人机上则是移动性感知的波束跟踪。最后，我们讨论了面向下一代NTN中可扩展、鲁棒且硬件高效的HBF的开放研究挑战和未来方向。
英文摘要
Hybrid analog-digital beamforming (HBF) has emerged as a key enabling technology for non-terrestrial networks (NTNs), where large antenna arrays are required to compensate for severe propagation loss but fully digital beamforming is often impractical due to radio-frequency (RF) chain cost, power consumption, and payload limitations. Compared with terrestrial networks, NTN platforms such as low Earth orbit (LEO) satellites and unmanned aerial vehicles (UAVs) impose distinctive HBF design challenges, including high mobility, Doppler effects, sparse line-of-sight-dominant channels, stringent on-board energy budgets, and, for UAVs, the additional coupling between beamforming and controllable platform placement or trajectory. This survey provides a systematic review of HBF techniques for NTN systems, with emphasis on LEO satellite and UAV communications. We first introduce common HBF architectures, signal models, channel representations, analog and digital precoder designs, and learning-aided approaches that form the shared technical foundation of existing works. We then survey both platforms under a common set of five categories, which cover system architecture and precoding design, time-varying beam management, network-level cooperation and scheduling, sensing capability and reconfigurable surfaces, and security and multiple access. Their platform-specific content differs most sharply in the second one, since the dominant time-varying mechanism is traffic-driven beam hopping on an LEO payload but mobility-aware beam tracking on a UAV. Finally, we discuss open research challenges and future directions toward scalable, robust, and hardware-efficient HBF in next-generation NTNs.
CommentsThis manuscript has been submitted to the IEEE Communications Surveys and Tutorials
