Multipath Effect On Non-Terrestrial Network

Multipath propagation significantly impacts Non-Terrestrial Networks (NTNs) by influencing signal integrity, delay spread, and K-factor behavior. This study analyzes multipath effects in NTNs using ray tracing simulations in Bologna, Italy, across urban, dense urban, and suburban environments. A broad frequency range (2 GHz, 3.5 GHz, 25 GHz, 40 GHz, and 50 GHz) and multiple polarization configurations (VV, HH, HV, VH, CV, VC, CH, CC, HC) are evaluated to assess their role in K-factor trends and delay spread behavior. The study also considers nine elevation angles (10°–90°) and six azimuth directions to ensure a detailed characterization of multipath propagation. Findings indicate that lower frequencies experience higher delay spread at low elevations due to strong multipath interactions and reflections, whereas higher frequencies (mmWave bands) transition rapidly to LOS dominance but are highly sensitive to depolarization and scattering, leading to sharper K-factor variations. Cross-polarized signals (HV, VH, CV, HC, CH, VC) exhibit distinct behaviors, emphasizing the importance of polarization selection in NTN performance. Dense urban environments sustain longer multipath delays, while suburban settings transition faster to LOS-dominant conditions due to fewer obstructions. These insights are crucial for enhancing satellite-to-ground communication when receivers are at street level in NLOS conditions. By refining NTN channel models with high-resolution frequency-dependent data, this study bridges the gap between theoretical modeling and real-world signal behavior, contributing to the optimization of NTN architectures for 5G, 6G, and satellite networks, ensuring more reliable and efficient wireless communications in complex urban environments.