Mathematical modeling for near-field 6G communications

Sammanfattning

The rapid growth of mobile communications and emerging technologies like extended reality (XR), Vehicle-to-Everything (V2X), and joint com- munications and sensing demands ultra-high data rates. To meet these requirements, research on future (Sixth-generation (6G) and beyond-6G) wireless networks is exploring Terahertz (THz, 300 Gigahertz (GHz) – 10 THz) and sub-Terahertz (sub-THz, 100 GHz – 300 GHz) bands as solutions to spectrum scarcity in currently used lower-frequency bands. One key challenge in these forthcoming THz and sub-THz wireless communication systems is distinguishing between near-field and far-field regions, as efficient communication techniques for these two ranges differ a lot (i.e., beamforming for the far field versus beamfocusing for the near field when using multi- antenna systems). The canonical model for this border distinction, the Fraunhofer distance equation, has limited applicability to practical sub-THz and THz communi- cation systems since the model is defined for point-source transmitters. This equation does not account for the complex geometries of phased antenna arrays nor antenna misalignment, which are essential for future (sub-)THz mobile communication systems. While previous studies have extended the Fraunhofer distance equation to address phased arrays Two-Dimensional (2D) and Three- Dimensional (3D) configurations, they do not take into account the effects of antenna misalignment relevant to real mobile communications scenarios. This thesis presents an extension of the canonical Fraunhofer distance model to incorporate antenna misalignment in both 2D and 3D configurations for phased antenna arrays. The extended model aims to more accurately define the near-field and far-field boundaries for (sub-)THz communication systems accounting for antenna misalignment. The research employs geometric modeling, trigonometric principles to develop the extended equation, computer simulations to validate the equation obtained and comparison with existing formulations to assess the effect of antenna misalignment. The key findings of this work demonstrate that the extended Fraunhofer distance models developed in this thesis successfully account for antenna misalignment. These results contribute to the optimization of communication systems in sub-THz and THz frequency bands, as it becomes possible to make more accurate decisions on near-field vs. far-field communication solutions to exploit in a particular configuration. The research outcomes open up new avenues for designing next-generation networks, particularly in optimizing communication across varying near-field and far-field regions, ultimately supporting the sustainability goals of future wireless technologies.