Ultra-dense low-Earth-orbit (LEO) satellite communication networks have significant potential for providing high-speed data services. To compensate the severe path loss in satellite communications, a key conceptual enabler is the holographic multiple input multiple output (HMIMO) with a spatially continuous aperture which can achieve a high directive gain with a small antenna size. In this paper, we consider a novel metamaterial antenna called a reconfigurable holographic surface (RHS) integrated with a user terminal (UT) to support LEO satellite communications. Composing of densely packing sub-wavelength metamaterial elements, the RHS can realize continuous or quasi-continuous apertures and provide a practical way towards the implementation of HMIMO. To obtain the desired beam directions towards the satellites, we propose a LEO satellite tracking scheme based on the temporal variation law such that frequent satellite positioning can be avoided. A holographic beamforming algorithm for sum rate maximization is then developed where a closed-form for the optimal holographic beamformer is derived. The robustness of the algorithm against the tracking errors of the satellites’ positions is also proved. Simulation results verify the theoretical analysis and show that the RHS outperforms the traditional phased array of the same physical dimension in terms of the sum rate when the compact element spacing of the RHS leads to much more RHS elements. Moreover, the RHS also provides a more cost-effective solution for pursuing high data rate compared with the phased array.

中文翻译：

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可重构全息表面辅助的 LEO 卫星通信全息 MIMO


超密集低地球轨道（LEO）卫星通信网络在提供高速数据服务方面具有巨大潜力。为了补偿卫星通信中严重的路径损耗，一个关键的概念推动者是具有空间连续孔径的全息多输入多输出（HMIMO），它可以通过小天线尺寸实现高定向增益。在本文中，我们考虑了一种称为可重构全息表面（RHS）的新型超材料天线，它与用户终端（UT）集成以支持LEO卫星通信。 RHS由密集排列的亚波长超材料元件组成，可以实现连续或准连续孔径，为HMIMO的实现提供了一种实用的方法。为了获得所需的卫星波束方向，我们提出了一种基于时间变化规律的低轨卫星跟踪方案，以避免频繁的卫星定位。然后开发了一种用于总速率最大化的全息波束形成算法，其中导出了最佳全息波束形成器的封闭形式。还证明了该算法对卫星位置跟踪误差的鲁棒性。仿真结果验证了理论分析，表明当RHS阵元间距紧凑导致RHS阵元数量更多时，RHS在总和速率方面优于相同物理尺寸的传统相控阵。此外，与相控阵相比，RHS还为追求高数据速率提供了更具成本效益的解决方案。