发表机构
University of Luxembourg; University of Rome Tor Vergata（卢森堡大学; 罗马托尔维加塔大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文提出可移动单元STAR-RIS（ME-STAR-RIS）用于6G非地面网络，通过结合全空间控制与表面几何重构增加空间自由度，并探讨架构、使能技术及挑战，数值案例显示其相对固定STAR-RIS的性能优势。
AI 中文摘要
非地面网络（NTN）正通过将无处不在且稳健的连接扩展到卫星、空中和地面层，成为6G系统的关键组成部分。然而，严重的传播损耗、快速变化的几何结构、多普勒效应、阻塞以及严格的载荷和能量约束，使得高效的波束和传播控制尤为具有挑战性。可移动单元STAR-RIS（ME-STAR-RIS）通过将全空间透射/反射控制与可重构表面几何结构相结合，提供了一种新方法，从而为几何感知的NTN操作引入了额外的空间自由度。在本文中，我们首先描述了ME-STAR-RIS的工作原理、移动约束和潜在的硬件实现，然后介绍了代表性的星载、空中中继和跨层NTN架构。我们讨论了关键使能机制，包括联合几何-电磁优化、移动感知信道获取、多时间尺度控制和预测性配置。一项以低轨卫星（LEO）为中心的数值案例研究将ME-STAR-RIS与完全相同的固定STAR-RIS进行了比较，展示了单元移动性在不同发射功率、移动范围和表面尺寸下的优势，同时揭示了日益增大的位移带来的收益递减。最后，我们讨论了主要的硬件、信道状态信息（CSI）、可扩展性、近场、感知、安全性、可靠性和标准化挑战，并强调了实现实用ME-STAR-RIS赋能NTN的有前景方向。
英文摘要
Non-terrestrial networks (NTNs) are emerging as a key component of 6G systems by extending ubiquitous and resilient connectivity across satellite, aerial, and terrestrial layers. However, severe propagation loss, rapidly varying geometry, Doppler, blockage, and stringent payload and energy constraints make efficient beam and propagation control particularly challenging. Movable-element STAR-RIS (ME-STAR-RIS) offers a new approach by combining full-space transmission/reflection control with reconfigurable surface geometry, thereby introducing an additional spatial degree of freedom for geometry-aware NTN operation. In this article, we first describe the operating principle, movement constraints, and potential hardware realizations of ME-STAR-RIS, and then present representative satellite-borne, aerial-relay, and cross-tier NTN architectures. We discuss the key enabling mechanisms, including joint geometry--electromagnetic optimization, mobility-aware channel acquisition, multi-timescale control, and predictive configuration. A LEO-centered numerical case study compares ME-STAR-RIS with an otherwise identical fixed STAR-RIS and demonstrates the benefit of element mobility across different transmit powers, movement ranges, and surface sizes, while revealing diminishing returns from increasingly large displacements. Finally, we discuss the main hardware, CSI, scalability, near-field, sensing, security, reliability, and standardization challenges, and highlight promising directions toward practical ME-STAR-RIS-enabled NTNs
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