The Landscape of Near-Field Communications: Pathways, Opportunities, and Challenges

With the rapid development of sixth generation (6G) mobile communication, the demands for terabit per second data rates and high-density connections have sharply increased, driving the adoption of innovative technologies such as extremely large-scale antenna arrays (ELAA) and terahertz (THz) spectrum. Built on this, near-field communication (NFC) has been introduced with spherical wave, which differs to the traditional channel modeling of far-field communication and renders existing methods such as plane wave assumption ineffective. Fortunately, near-field beamfocusing can concentrate energy at a specific point in space by controlling the spherical wave, significantly improving the transmission performance. Therefore, to fully clarify the superior energy positioning and high spatial resolution characteristics of NFC, we firstly elaborate the boundary between near-field and far-field region, the features of beamfocusing, novel structure and design of antenna array, and cross-field transmission schemes. Following that, the integrations of emerging technologies and NFC are explored, including of reconfigurable intelligent surface (RIS), integrated sensing and communication (ISAC), multiple access, and physical layer security (PLS). In addition, the antenna array design is studied by a simple case, where the optimal shape of array is obtained. Moreover, the challenges of NFC are provided to support the future ultra dense networks and secure Internet of Things (IoT), such as accurate near-field channel modeling, effective channel estimation, challenges of practical deployment, and artificial intelligence (AI) utilization of NFC.