The emerging space-air-ground integrated network has attracted intensive research and necessitates reliable and efficient aeronautical communications. This paper investigates terahertz Ultra-Massive (UM)-MIMO-based aeronautical communications and proposes an effective channel estimation and tracking scheme, which can solve the performance degradation problem caused by the unique {\emph{triple delay-beam-Doppler squint effects}} of aeronautical terahertz UM-MIMO channels. Specifically, based on the rough angle estimates acquired from navigation information, an initial aeronautical link is established, where the delay-beam squint at transceiver can be significantly mitigated by employing a Grouping True-Time Delay Unit (GTTDU) module (e.g., the designed {\emph{Rotman lens}}-based GTTDU module). According to the proposed prior-aided iterative angle estimation algorithm, azimuth/elevation angles can be estimated, and these angles are adopted to achieve precise beam-alignment and refine GTTDU module for further eliminating delay-beam squint. Doppler shifts can be subsequently estimated using the proposed prior-aided iterative Doppler shift estimation algorithm. On this basis, path delays and channel gains can be estimated accurately, where the Doppler squint can be effectively attenuated via compensation process. For data transmission, a data-aided decision-directed based channel tracking algorithm is developed to track the beam-aligned effective channels. When the data-aided channel tracking is invalid, angles will be re-estimated at the pilot-aided channel tracking stage with an equivalent sparse digital array, where angle ambiguity can be resolved based on the previously estimated angles. The simulation results and the derived Cram\'{e}r-Rao lower bounds verify the effectiveness of our solution.
翻译:正在形成的空空综合网络吸引了大量研究,需要可靠和高效的航空通信。 具体地说, 根据从导航信息中获得的粗角度估计, 建立了一个初始的航空链接, 通过使用一个名为“ tremph{ triple later- beam- Doppler squtr communication community communication, 并提议一个有效的频道估算和跟踪系统, 从而解决由独特的 emph{ triple- beam- Doppler compatial communical communical complical complication, 建立初始的航空连接, 通过使用一个名为“ Ulight- be massion loadal directive” 的延迟数据分析器来大大降低运行延迟- 。 设计了一个名为“ xemphetropplemill- locelectiveal commodeal lider ”, 可以在一个预设的迭交错点上进行计算, 可以估算, 并且采用这些角度可以实现精确的对等等值的对等值的转换。