• beyond 5G
• non linearities
• ofdm
• sub-thz

With the fast development of smart terminals and emerging new applications (e.g., real-time and interactive services), wireless data traffic has drastically increased, and current cellular networks cannot completely match the quickly rising technical requirements. Historically, a new mobile generation appears every ten years. So, 6G is expected to emerge around 2030.

THz (0.1-10 THz) is recognized as a highly promising technology for 6G, thanks to:

- tens-hundreds gigahertz of contiguous bandwidth;
- ease of coexistence with other regulated spectra.


Due to its expansive bandwidth, Terahertz (THz) technology extends the quality of experience typically associated with fiber-optic systems to wireless connections. This translates to connectivity capable of delivering extremely high data rates (Tbps) with consistent performance, ensuring reliability and meeting latency requirements. However, employing THz waves presents significant challenges, primarily due to severe propagation losses that restrict communication coverage.
The THz band has traditionally been one of the least explored frequency bands in the electromagnetic (EM) spectrum, mostly due to the lack of efficient and practical THz transceivers and antennas. Nevertheless, to expedite the way of fulfilling this gap, practical THz communication systems are being enabled by the major progress in the last ten years.
Traditionally, the lack of compact energy-efficient high power THz transmitters and low-noise high-sensitivity receivers has limited the practical use of the THz band
for communication systems.

Radio Frequency (RF) building block performance generally degrades with increasing frequency. The power capability of power amplifiers for a given integrated circuit technology roughly degrades by 20 dB per decade.
There is a fundamental cause for this degradation; increased power capability and increased frequency capability are conflicting requirements as observed from the so-called Johnson limit. In short, higher operational frequencies require smaller geometries, which subsequently result in lower operational power in order to prevent dielectric breakdown from the increased field strengths. Moore’s Law does not favor power capability performance.
A remedy is however found in the choice of integrated circuit material. THz integrated circuits have traditionally been manufactured using so called III-V materials, i.e. a combination of elements from groups III and V of the periodic table, such as Gallium Arsenide (GaAs) and more recently Gallium Nitride (GaN). Integrated circuit technologies based on III-V materials are substantially more expensive than conventional silicon-based technologies and they cannot handle the integration complexity of e.g. digital circuits or radio modems for cellular handsets. Nevertheless, GaN-based technologies are now maturing rapidly and deliver power levels an order of magnitude higher compared to conventional technologies.


Additionally, there remains considerable uncertainty regarding the most efficient waveform for THz communications. The high-frequency nature of THz waves exacerbates issues like phase noise, nonlinear distortions, and high peak-to-average power ratios (PAPR), making traditional waveforms, such as those used in lower frequency bands, potentially less effective.

This thesis aims to conduct a comprehensive study of the performance and behavior of two amplifiers operating at different frequencies within both Orthogonal Frequency-Division Multiplexing (OFDM) and Single Carrier (SC) systems. By examining the operation of these amplifiers, the research seeks to provide a detailed comparison between these two communication paradigms, specifically in the context of Terahertz (THz) frequencies. The goal is to offer a clear and thorough understanding of the advantages and limitations of operating at THz frequencies, focusing on key aspects such as signal integrity, power efficiency, and overall system performance.

In addition, this study aims to evaluate the performance of both considered waveforms, particularly in terms of their resilience to nonlinearities and other challenges that arise at higher frequencies. Ultimately, this work aspires to contribute to the ongoing development of THz technology by laying the groundwork for future research. It also aims to highlight areas for further exploration, such as the inclusion of realistic channel models, phase noise effects, and I/Q imbalance modeling, all of which will be crucial in the search for the optimal waveform for next-generation communication systems.