On the Occurrence of Two-Wave with Diffuse Power Fading in MillimeterWave Communications

Mobile communications has become so successful today that conventional radio technologies, in traditional frequency bands below 6 GHz, are soon reaching their limits. To be able to develop massively deployed, ubiquitous, data-hungry, mobile applications, this study explores the use of higher frequency bands, or so-called millimeter waves in mobile communications. These radio bands above 30 GHz are mostly unoccupied and have dozens of gigahertz of bandwidth available. Moreover, advances in electronics have now made it possible to utilize these bands cost effectively. This thesis studied the millimeter wave wireless channel through conducting the following experiments: (1) two indoor millimeter wave measurement campaigns with directive horn antennas on both link ends, (2) an outdoor vehicular millimeter wave measurement campaign employing a horn antenna and an omni directional antenna, and (3) a railway communications ray-tracing study with directive antennas on both sides. In all the cases, the data obtained show that the millimeter wave wireless channel has very limited multipath propagation. The main reason for the absence of a rich multipath propagation is because the millimeter wave wireless channel requires high-gain directive antennas that compensate for the path loss. These directive antennas act as spatial filters, thereby effectively reducing the number of significant multipath components. All the cases presented in this thesis are characterized by one or two dominant multipath components. Small-scale fading is hence adequately modeled with a model named two-wave with diffuse power (TWDP). This TWDP model captures the effect of interference of two non-fluctuating radio signals and of many smaller so-called diffuse signals. A delay-Doppler analysis is also performed in this research based on the data obtained from the vehicular measurement campaign. The analysis reveals that the high maximum Doppler shift is not reflected in the Doppler spread values. Again, the effects of the Doppler shift in this setup are suppressed due to spatial filtering. Lastly, this thesis briefly addresses the modeling of the TWDP model parameters for a simplified railway communications scenario, and demonstrates the implications of TWDP fading through numerical simulations.