To support the extremely high spectral efficiency and energy efficiency requirements, and emerging applications of future wireless communications, holographic multiple-input multiple-output (H-MIMO) technology is envisioned as one of the most promising enablers. It can potentially bring extra degrees-of-freedom for communications and signal processing, including spatial multiplexing in line-of-sight (LoS) channels and electromagnetic (EM) field processing performed using specialized devices, to attain the fundamental limits of wireless communications. In this context, EM-domain channel modeling is critical to harvest the benefits offered by H-MIMO. Existing EM-domain channel models are built based on the tensor Green function, which require prior knowledge of the global position and/or the relative distances and directions of the transmit/receive antenna elements. Such knowledge may be difficult to acquire in real-world applications due to extensive measurements needed for obtaining this data. To overcome this limitation, we propose a transmit-receive parameter separable channel model methodology in which the EM-domain (or holographic) channel can be simply acquired from the distance/direction measured between the center-points between the transmit and receive surfaces, and the local positions between the transmit and receive elements, thus avoiding extensive global parameter measurements. Analysis and numerical results showcase the effectiveness of the proposed channel modeling approach in approximating the H-MIMO channel, and achieving the theoretical channel capacity.

翻译：为支撑未来无线通信极高的频谱效率和能量效率需求及新兴应用，全息多输入多输出（H-MIMO）技术被视为最具前景的关键使能技术之一。该技术有望为通信与信号处理带来额外自由度，包括直视（LoS）信道中的空分复用以及利用专用器件实现的电磁（EM）场处理，从而逼近无线通信的极限性能。在此背景下，电磁域信道建模对于充分发挥H-MIMO技术的优势至关重要。现有电磁域信道模型基于张量格林函数构建，需要预先获取发射/接收天线单元的全局位置和/或相对距离与方向信息。在实际应用中，上述参数的获取需进行大量测量，导致实现困难。为突破这一限制，我们提出一种收发参数可分离信道建模方法，该方法仅需通过发射端与接收端曲面中心点间的距离/方向测量，以及收发单元间的局部位置信息即可简单获取电磁域（或全息）信道，从而避免繁复的全局参数测量。分析与数值结果表明，所提信道建模方法能够有效逼近H-MIMO信道，并实现理论信道容量。