Sixth-generation (6G) networks are expected to provide ubiquitous connectivity across terrestrial and non-terrestrial domains. This will be possible by integrating non-terrestrial networks (NTNs) to extend coverage to underserved areas. Antennas are central to this vision, with multiple-input multiple-output (MIMO) technologies receiving the most attention due to their ability to exploit spatial multiplexing to improve link capacity and reliability. However, conventional MIMO can consume significant energy, as each antenna element typically requires an independent RF chain. This limitation is particularly critical in non-terrestrial systems, where onboard energy resources are limited. Holographic MIMO (HMIMO) has emerged as a promising alternative in this context. These systems are based on theoretically continuous apertures, where radiation is generated through controlled modulation of surface impedance. This enables beamforming mechanisms with significantly fewer RF chains, reducing power consumption. In this work, we make the case for HMIMO as a suitable candidate for NTN integration within IMT-2030 systems. We discuss its advantages over conventional MIMO and present a case study of HMIMO integration in LEO-based multi-user communication.

翻译：第六代（6G）网络有望在地面与非地面域提供泛在连接。通过集成非地面网络（NTN）扩展覆盖至服务欠缺区域，这一目标将得以实现。天线是实现这一愿景的核心要素，其中多输入多输出（MIMO）技术因能够利用空间复用提升链路容量与可靠性而备受关注。然而，传统MIMO会消耗大量能量，因为每个天线单元通常需要独立的射频链路。这一限制在非地面系统中尤为关键——此类系统星载能量资源极其有限。在此背景下，全息MIMO（HMIMO）作为一种具有前景的替代方案应运而生。该技术基于理论连续孔径，通过表面阻抗受控调制产生辐射，从而以显著更少的射频链路实现波束赋形机制，降低功耗。本文论证了HMIMO作为IMT-2030系统中NTN融合候选方案的适用性，探讨了其相较传统MIMO的优势，并给出了低轨卫星多用户通信中HMIMO集成的案例研究。