Sixth-generation (6G) mobile communication networks are expected to have dense infrastructures, large-dimensional channels, cost-effective hardware, diversified positioning methods, and enhanced intelligence. Such trends bring both new challenges and opportunities for the practical design of 6G. On one hand, acquiring channel state information (CSI) in real time for all wireless links becomes quite challenging in 6G. On the other hand, there would be numerous data sources in 6G containing high-quality location-tagged channel data, making it possible to better learn the local wireless environment. By exploiting such new opportunities and for tackling the CSI acquisition challenge, there is a promising paradigm shift from the conventional environment-unaware communications to the new environment-aware communications based on the novel approach of channel knowledge map (CKM). This article aims to provide a comprehensive tutorial overview on environment-aware communications enabled by CKM to fully harness its benefits for 6G. First, the basic concept of CKM is presented, and a comparison of CKM with various existing channel inference techniques is discussed. Next, the main techniques for CKM construction are discussed, including both the model-free and model-assisted approaches. Furthermore, a general framework is presented for the utilization of CKM to achieve environment-aware communications, followed by some typical CKM-aided communication scenarios. Finally, important open problems in CKM research are highlighted and potential solutions are discussed to inspire future work.

翻译：第六代（6G）移动通信网络预计将具备密集基础设施、大维度信道、低成本硬件、多样化定位方法和增强智能等特征。这些趋势为6G的实际设计带来了新的挑战与机遇。一方面，在6G中实时获取所有无线链路的信道状态信息变得极为困难。另一方面，6G中将涌现大量包含高精度位置标签信道数据的数据源，使得更深入地学习本地无线环境成为可能。为利用这一新机遇并应对信道状态信息获取挑战，一种从传统环境非感知通信到基于信道知识地图这一创新方法的环境感知通信的范式转变已然显现。本文旨在提供基于CKM实现环境感知通信的全面教程性综述，以充分释放其在6G中的潜力。首先介绍CKM的基本概念，并讨论其与现有多种信道推断技术的差异。随后阐述CKM构建的核心技术，包括无模型和模型辅助两类方法。进一步地，提出利用CKM实现环境感知通信的通用框架，并展示若干典型CKM辅助通信场景。最后，重点指出CKM研究中亟待解决的关键问题，探讨潜在解决方案以启发未来研究。