By integrating a nearly infinite number of reconfigurable elements into a finite space, a spatially continuous array aperture is formed for holographic multiple-input multiple-output (HMIMO) communications. This three-part tutorial aims for providing an overview of the latest advances in HMIMO communications. As Part I of the tutorial, this letter first introduces the fundamental concept of HMIMO and reviews the recent progress in HMIMO channel modeling, followed by a suite of efficient channel estimation approaches. Finally, numerical results are provided for demonstrating the statistical consistency of the new HMIMO channel model advocated with conventional ones and evaluating the performance of the channel estimators. Parts II and III of the tutorial will delve into the performance analysis and holographic beamforming, and detail the interplay of HMIMO with emerging technologies.

翻译：通过在有限空间内集成近乎无限数量的可重构单元，形成了用于全息多输入多输出（HMIMO）通信的空间连续阵列孔径。本三部分教程旨在概述HMIMO通信领域的最新进展。作为教程的第一部分，本文首先介绍了HMIMO的基本概念，并回顾了HMIMO信道建模的最新进展，随后介绍了一系列高效的信道估计方法。最后，通过数值结果验证了所提出的新型HMIMO信道模型与传统模型之间的统计一致性，并评估了信道估计器的性能。教程的第二部分和第三部分将深入探讨性能分析与全息波束赋形，并详细介绍HMIMO与新兴技术的相互作用。