Abstract
The emerging sixth generation (6G) of cellular networks are expected to use
a wide range of spectrum, including millimeter wave (mmWave), terahertz
(THz), and optical spectrum, to support ultra-data rates and low-latency ap
plications such as extended reality (XR) services and connected autonomous
systems. However, the directional nature of these bands introduces chal
lenges such as severe path loss, sensitivity to blockages, complex hardware
requirements, and strict beam alignment. In addition, the regulatory and
standardization landscape for these bands remains incomplete. This thesis
investigates these spectrum bands and beam alignment challenges through
two complementary research directions.
First, a comprehensive survey of 6G spectrum options is conducted, an
alyzing spectrum allocation approaches and the status of standardization
efforts for mmWave, THz, and optical wireless communication (OWC) tech
nologies. Second, the thesis develops an information-aware beam alignment
error model in mmWave. The proposed model introduces a novel alignment
information parameter to quantify the available directional knowledge and
jointly determine the variance and truncation boundaries, enabling a contin
uous transition from uniform error (no information) to truncated Gaussian
(partial information) and to a Dirac delta function (near-perfect informa
tion). An antenna inefficiency factor accounts for hardware imperfections.
Using stochastic geometry, downlink coverage probability is derived for both
omni-antenna and directional antenna users, and a discrete-gain approxima
tion is proposed to enable tractable analysis under cosine antenna patterns.
In summary, this thesis contributes to the understanding of high-frequency
6G networks by examining the opportunities, challenges, spectrum manage
ment considerations, and standardization status of mmWave, THz, and OWC
technologies, while also demonstrating how alignment information influences
beamwidth selection and coverage performance in mmWave systems.
