As the backbone of the fifth-generation (5G) cellular network, massive multiple-input multiple-output (MIMO) encounters a significant challenge in practical applications: how to deploy a large number of antenna elements within limited spaces. Recently, holographic communication has emerged as a potential solution to this issue. It employs dense antenna arrays and provides a tractable model. Nevertheless, some challenges must be addressed to actualize this innovative concept. One is the mutual coupling among antenna elements within an array. When the element spacing is small, near-field coupling becomes the dominant factor that strongly restricts the array performance. Another is the polarization of electromagnetic waves. As an intrinsic property, it was not fully considered in the previous channel modeling of holographic communication. The third is the lack of real-world experiments to show the potential and possible defects of a holographic communication system. In this paper, we propose an electromagnetic channel model based on the characteristics of electromagnetic waves. This model encompasses the impact of mutual coupling in the transceiver sides and the depolarization in the propagation environment. Furthermore, by approximating an infinite array, the performance restrictions of large-scale dense antenna arrays are also studied theoretically to exploit the potential of the proposed channel. In addition, numerical simulations and a channel measurement experiment are conducted. The findings reveal that within limited spaces, the coupling effect, particularly for element spacing smaller than half of the wavelength, is the primary factor leading to the inflection point for the performance of holographic communications.

中文翻译：

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致密 MIMO：全息通信的信道建模、物理约束和性能评估


作为第五代（5G）蜂窝网络的骨干，大规模多输入多输出（MIMO）在实际应用中遇到了重大挑战：如何在有限的空间内部署大量天线单元。最近，全息通信成为解决这一问题的潜在方案。它采用密集的天线阵列并提供易于处理的模型。然而，要实现这一创新概念，必须解决一些挑战。一是阵列内天线单元之间的相互耦合。当阵元间距较小时，近场耦合成为强烈限制阵列性能的主导因素。另一个是电磁波的极化。作为一种内在属性，在之前的全息通信通道建模中并没有充分考虑到它。第三是缺乏现实世界的实验来展示全息通信系统的潜力和可能的缺陷。在本文中，我们根据电磁波的特性提出了一种电磁信道模型。该模型涵盖了收发器侧的互耦和传播环境中的去极化的影响。此外，通过近似无限阵列，还从理论上研究了大规模密集天线阵列的性能限制，以开发所提出的信道的潜力。此外，还进行了数值模拟和通道测量实验。研究结果表明，在有限的空间内，耦合效应，特别是元件间距小于波长一半的耦合效应，是导致全息通信性能拐点的主要因素。