Characterizing Multipath Radio Environments for 5G Wireless Systems and Beyond

The envelope of performance in Fifth generation (5G) technology will be much greater than what we see in legacy technologies, featuring low latency, ultra-high data rates, massive connectivity, and increased security. 5G wireless systems operating in centimeter (cm) and millimeter (mm) wave parts of the frequency spectrum must deal with all sorts of radio wave propagation conditions imposed by a radio channel. This entails thoroughly characterizing radio channels across the desired frequency range for efficient system design and performance. The primary focus of this thesis is (1) to model the interaction of radio waves with material objects in radio environments, and (2) to characterize multipath radio channels at cmWave and mmWave frequencies. The key contributions of the thesis are summarized as follows. First, a comprehensive evaluation of transmission and reflection losses for material objects in built environments is carried out at the 70 GHz frequency band. The results demonstrate that energy-efficient building windows, laminated plywood, and plasterboard are good reflectors of mmWave signals, while humans and some energy-efficient windows attenuate mmWave signals as high as 40 dB. Second, a novel method is proposed for the on-site estimation of the permittivity of built-in materials using the point cloud geometrical database and limited channel measurements of a given radio environment. The estimated material permittivities of a large indoor office are visualized through a colored three-dimensional (3D) point cloud map of the environment. Third, human blockage losses are measured through anechoic chamber measurements for 15 human subjects with different weights and sizes at 15, 28, and 60 GHz frequency bands. Moreover, a novel double-truncated multiple knife-edge (DTKME) model is proposed that reasonably predicts the measured human blockage loss for different body orientations and illuminating antenna heights. Fourth, the feasibility of applying full-wave numerical techniques for coverage predictions is determined by finite-difference time-domain (FDTD) simulations for the coverage analysis inside a small indoor office. It is transpired that the full-wave methods are computationally expensive, and a trade-off exists between the accuracy and complexity of these simulations. Finally, multipath characterization of cmWave and mmWave radio channels is performed for indoor and outdoor radio environments in terms of their power, delay, and angular domain behavior. The fluctuations in the signal envelope of mmWave channels are more significant than their cmWave counterparts. The mmWave channels exhibit less delay dispersion compared to cmWave radio channels. The spatial spread of multipath is similar in line-of-sight (LOS) conditions across cmWave and mmWave radio channels, while in non-LOS (NLOS) propagation conditions, the cmWave radio channels offer more spatial spread of multipath than mmWave radio channels.