Ray-Tracing Channel Models for Near-Field Communication

Abstract

Extremely large-scale multiple-input multiple-output (XL-MIMO) and Terahertz-band communications (THz) are widely considered as key potential enabling technologies for sixthgeneration (6G) wireless networks to achieve their ambitious performance targets. Those advanced technologies induce a paradigm shift in the electromagnetic characteristics, such as a significant expansion of the near-field region, thereby redefining the 6G propagation model. The intrinsic differences between near-field and far-field wave propagation models introduce new challenges for near-field communications (NFC), particularly in accurately characterizing the underlying channel’s properties. Firstly, this article begins with an investigation into the complex phenomena induced by 6G.
enabling technologies and distinctive electromagnetic regions. We then provide rigorous derivations of
ray-tracing channel models for two widely adopted antenna array architectures, explicitly accounting
for the unique propagation characteristics of radiating near-field regions, and also contrast them with
the ongoing 3GPP standardization efforts. We also conduct a systematic review of the channel models
used in recent progress in channel estimation, and align them with our presented models. Finally, we
offer an overview that addresses key challenges and highlights emerging opportunities for NFC within
the 6G paradigm.