High frequency propagation in large and multiply connected electromagnetic environments

Emergent wireless telecommunications and 5G mobile networks will operate at very high frequencies, ranging from microwave (5GHz) to mmWave (28GHz and beyond) regimes. Indoor coverage is challenging at these frequencies, where environments are expected to be highly overmoded. We perform full-wave Transmission Line Matrix simulations of a test electromagnetic environment. For electrically large, multiply connected rooms with simple polygonal irregularities, e.g. blades, we show that different regimes occur in the spatial field pattern as the frequency increases. From 1 GHz to 5 GHz the pattern is speckled. At 8 and 12 GHz we observe the emergence of specular components existing on a noisy background. The statistics of fields in the background are important for small scale fading in non-line-of-sight conditions. We characterize the spatial statistics of the test environment. Because of coupling and partially regular boundary, fluctuations acquire non-generic features, and they result in non-Rayleigh distribution functions at the investigated frequencies. The resurgence of directionality in the high microwave regime has an effect in fading statistics in a similar way of shadowing, from which background field statistics are fitted by fat tail (Bessel K) distribution. However, since the transition from low to high microwave regimes has no defined separation between specular and noisy components, generated by reflection and diffraction, ray tracing algorithms - more appropriate to predict energy of specular components - need to be extended to cope with noisy fields. We envisage these methods to be fundamental in the description of mmWave propagation. The achieved results are useful to create channel models for the outdoor-to-indoor transition and to extend mobile signal coverage to indoor regions.