A Tutorial on Near-Field Driven 6G Networks

Integrating large-scale antenna arrays is essential for overcoming capacity limitations in wireless communications. This article examines secure wireless information and power transfer (SWIPT) within a near-field massive multiple-input singleoutput (MISO) system using extremely large-scale antenna arrays (ELAA). Traditional polar models inadequately capture realistic near-field propagation effects, so we adopt a three-dimensional (3D) spherical geometry for a more accurate representation. Our system simultaneously delivers power and information to zero-energy devices (ZEDs) via non-orthogonal multiple access (NOMA), while an eavesdropper (EVE) attempts to intercept confidential data. We formulate a non-convex optimization problem to maximize the secrecy rate while ensuring minimum quality-of-service (QoS) and energy-harvesting requirements for ZEDs. An iterative algorithm based on weighted sum-rate maximization and sequential convex approximations effectively mitigates strong interference through NOMA and beamfocusing techniques. Numerical simulations reveal that, with a 64-element uniform linear array (ULA) antenna and 40 dBm transmit power, near-field NOMA achieves a 18.41% higher secrecy rate than near-field spatial division multiple access (SDMA) and a remarkable 36.78-fold improvement over near-field orthogonal multiple access (OMA). Additionally, beamfocusing enhances harvested power by 6.39 dBm relative to SDMA. These findings underscore the importance of accurately modeling near-field spherical wavefronts in next-generation 6G networks, where densely packed antenna arrays at higher frequencies are crucial for short-range communication and expansive Internet of Things (IoT) applications. Furthermore, the implications extend beyond theoretical insights, particularly in industrial IoT networks and Industry 4.0 deployments, where achieving energy efficiency, security, and sustainability in dense, high-frequency communication environments is critical.