The design dilemma of "What will be different between near-field communications (NFC) and far-field communications (FFC)?" is addressed from four perspectives. 1) From the channel modelling perspective, the differences between near-field and far-field channel models are discussed. A novel Green's function-based channel model is proposed for continuous-aperture antennas, which is contrasted to conventional channel models tailored for spatially-discrete antennas. 2) From the performance analysis perspective, analytical results for characterizing the degrees of freedom and the power scaling laws in the near-field region are provided for both spatially-discrete and continuous-aperture antennas. 3) From the beamforming perspective, far-field beamforming is analogous to a "flashlight" that enables beamsteering, while near-field beamforming can be likened to a "spotlight" that facilitates beamfocusing. As a further advance, a couple of new beamforming structures are proposed for exploiting the new characteristics of NFC. 4) From the application perspective, new designs are discussed in the context of promising next-generation technologies in NFC, where our preliminary numerical results demonstrate that distance-aware target sensing and enhanced physical layer security can be realized in NFC. Finally, several future research directions of NFC are discussed.

翻译：关于“近场通信（NFC）与远场通信（FFC）究竟有何不同”的设计困境，本文从四个角度予以阐释。1）从信道建模角度，讨论近场与远场信道模型之间的差异。针对连续孔径天线提出一种基于格林函数的新型信道模型，并与针对空间离散天线设计的传统信道模型形成对比。2）从性能分析角度，针对空间离散天线与连续孔径天线，给出表征近场区域自由度与功率缩放定律的解析结果。3）从波束成形角度，远场波束成形可类比为“手电筒”实现波束转向，而近场波束成形则类似于“聚光灯”实现波束聚焦。作为进一步发展，提出若干新型波束成形结构以利用近场通信的新特性。4）从应用角度，探讨近场通信背景下具有前景的下一代技术设计，初步数值结果表明近场通信可实现距离感知目标检测与增强的物理层安全。最后，讨论近场通信的若干未来研究方向。