Design and Analysis of Non-Orthogonal Multiple Access Techniques for Terahertz Networks

Fueled by the emergence of machine-type communications in a variety of wireless applications, the provisioning of massive connectivity becomes instrumental. On the other hand, accommodating trillions of devices within the extremely congested and limited sub-6GHz spectrum is becoming challenging. In this context, shifting to higher frequency terahertz (THz) communication is under consideration to obtain the data rates in the order of hundreds of gigabits per second (Gbps). Also, non-orthogonal multiple access schemes are becoming popular to support multiple users in the same frequency and time resource block, while leveraging on efficient interference cancellation mechanisms. In this thesis, I develop a comprehensive mathematical framework to analyze the performance of emerging non-orthogonal channel access schemes, such as non-orthogonal multiple access (NOMA) and rate-splitting multiple access (RSMA), in THz networks. In the first part of the thesis, I develop a statistical framework to analyze the performance of NOMA in the downlink of a single-carrier and multi-carrier THz network considering Nakagami-m fading and molecular absorption noise. In this context, I first develop a novel user pairing scheme which ensures the performance gains of NOMA over orthogonal multiple access (OMA) for each individual user in the NOMA pair and adapts according to the THz molecular absorption. Then, I characterize novel outage probability expressions considering a single-carrier and multi-carrier THz-NOMA network in the presence of various user pairing schemes, Nakagami-m channel fading, and molecular absorption noise. Specifically, I propose a moment-generating-function (MGF) based approach to analyze the outage probability of users in a multi-carrier THz network. For negligible thermal noise, I provide simplified single-integral expression to compute the outage in a multi-carrier network. Numerical results demonstrate the efficiency of the proposed user-pairing scheme compared to the existing benchmarks and validate the accuracy of the derived expressions. Finally, in the second part of the thesis, I extend the developed framework to analyze the performance of RSMA in the downlink transmission of Sub-6 GHz and THz networks.