The "near-field" propagation modeling of wireless channels is necessary to support sixth-generation (6G) technologies, such as intelligent reflecting surface (IRS), that are enabled by large aperture antennas and higher frequency carriers. As the conventional far-field model proves inadequate in this context, there is a pressing need to explore and bridge the gap between near and far-field propagation models. Although far-field models are simple and provide computationally efficient solutions for many practical applications, near-field models provide the most accurate representation of wireless channels. This paper builds upon the foundations of electromagnetic wave propagation theory to derive near and far-field models as approximations of the Green's function (Maxwell's equations). We characterize the near and far-field models both theoretically and with the help of simulations in a line-of-sight (LOS)-only scenario. In particular, for two key applications in multiantenna systems, namely, beamforming and multiple-access, we showcase the advantages of using the near-field model over the far-field, and present a novel scheduling scheme for multiple-access in the near-field regime. Our findings offer insights into the challenge of incorporating near-field models in practical wireless systems, fostering enhanced performance in future communication technologies.

翻译：无线信道的“近场”传播建模对于支持第六代（6G）技术（例如智能反射表面（IRS））至关重要，这些技术得益于大孔径天线和更高频率载波。由于传统远场模型在此背景下显得不足，因此迫切需要探索并弥合近场与远场传播模型之间的差距。尽管远场模型简单，能为许多实际应用提供计算高效的解决方案，但近场模型提供了无线信道最准确的表征。本文基于电磁波传播理论的基础，推导了近场和远场模型作为格林函数（麦克斯韦方程组）的近似。我们从理论和仿真两方面，在仅视距（LOS）场景下表征了近场和远场模型。特别是，针对多天线系统中的两个关键应用——波束赋形和多址接入——我们展示了使用近场模型优于远场模型的优势，并提出了一种近场环境下多址接入的新颖调度方案。我们的研究结果为在实用无线系统中融入近场模型这一挑战提供了见解，从而促进未来通信技术的性能提升。