The far-field channel model has historically been used in wireless communications due to the simplicity of mathematical modeling and convenience for algorithm design. With the need for high data rates, low latency, and ubiquitous connectivity in the sixth generation (6G) of communication systems, new technology enablers such as extremely large antenna arrays (ELAA), reconfigurable intelligent surfaces (RISs), and distributed multiple-input-multiple-output (D-MIMO) systems will be adopted. These enablers not only aim to improve communication services but also have an impact on localization and sensing (L&S), which are expected to be integrated into future wireless systems. Despite appearing in different scenarios and supporting different frequency bands, these enablers share the so-called near-field (NF) features, which will provide extra geometric information. In this work, we describe the NF features, namely, the spherical wave model, spatial non-stationarity, and beam squint effect. After discussing how L&S see NF differently from communication, the opportunities and open research challenges are provided.

翻译：历史上，远场信道模型因数学建模简单且便于算法设计，被广泛应用于无线通信。随着第六代（6G）通信系统对高数据速率、低时延及全域连接的需求，超大规模天线阵列（ELAA）、可重构智能超表面（RIS）及分布式多输入多输出（D-MIMO）系统等新型技术使能器将被采用。这些使能器不仅旨在提升通信服务质量，还将对定位与感知（L&S）产生深远影响——而这两者预计将集成于未来无线系统中。尽管这些使能器应用于不同场景并支持不同频段，但它们均具备所谓的近场（NF）特征，这一特征将提供额外的几何信息。本文描述了近场的三大核心特征：球面波模型、空间非平稳性及波束斜视效应。在探讨L&S如何从通信视角理解近场差异后，本文进一步阐述了相关机遇与开放性研究挑战。