Sub-terahertz (Sub-THz) communication is considered as a key enabler for sixth-generation (6G) and beyond communication systems, owing to its abundant spectrum resources that support extreme data rates, high spatial resolution, and low latency. However, the unfavorable propagation characteristics and significant hardware impairments pose substantial challenges to practical deployment, often resulting in high implementation costs.

Current commercial communication systems predominantly rely on colocated multiple-input multiple-output (MIMO) architectures to provide high spectral efficiency and reliable service. At sub-THz frequencies, although the severe free-space path loss can be largely compensated by large antenna arrays and highly directional beamforming, the susceptibility to blockage remains a fundamental limitation of co-located MIMO systems. Due to the strong dependence on a dominant line-of-sight path and the co-located nature of the antenna elements, obstruction by human bodies, objects, or environmental dynamics can simultaneously degrade all antenna links, resulting in abrupt signal attenuation and intermittent connectivity. Moreover, the pronounced hardware impairments at sub-THz frequencies, such as power amplifier (PA) inefficiency, phase noise, and limited data-converter resolution,increase system complexity and implementation cost, thereby challenging the practical deployment of co-located MIMO architectures in mobile sub-THz communications.

Recent advancements in polymer microwave fiber (PMF) technology have created significant opportunities for robust, low-cost, and high-speed sub-THz radio-over-fiber (RoF) communications. As an alternative, novel RoF architectures can facilitate cost-effective realization of sub-THz systems.

Recognizing these potential benefits, this thesis explores a novel RoF structure that interconnects multiple radio units (RUs), booster units (BUs), and a central unit (CU) in cascade via PMF, envisioning its application in indoor scenarios. This structure creates several research opportunities when considering cascaded distortion effects introduced by non-linear PAs and the propagation channel over the fiber.

Within this context, the contributions of this thesis are twofold.

i) Uplink positioning: We propose uplink positioning algorithms that exploit the cumulative effects of cascaded non-linear PAs and dispersive PMFs. Specifically, we develop maximum-likelihood and non-linear least-squares estimators to determine the entry RU and the time-of-arrival between the RoF system and the user equipment, where identifying the entry RU corresponds to estimating the signal propagation distance along the RoF stripe. For the special case of linear PAs, we derive the Cramér–Rao lower bound (CRLB)to benchmark estimator performance. Our simulation results demonstrate that the proposed estimators remain effective even under cascaded non-linear distortions, and that the architecture enables cost-efficient, high-resolution indoor positioning. In the numerical evaluations, experimentally measured PMF characteristics for high-density polyethylene fibers are also incorporated.

ii) Waveform selection: We introduce a set of candidate waveforms and compare them using multiple performance metrics to assess their robustness against hardware impairments. The considered waveforms are categorized into three operational regimes, each associated with a distinct system configuration. Several waveforms are then generated and evaluated within the considered cascade-structured RoF Sub-THz system. Importantly, we provide new insights and an in-depth comparative analysis of the dominant characteristics of each waveform, highlighting the most suitable option for the envisioned architecture and offering a detailed complexity assessment.