Applications and challenges of free-space optics for next-generation wireless communications

• Autor(a) principal: Nascimento, José Leonardo Bernardes
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/32521
• topic: Free-space optics; Optical beam steering; Data-center interconnects; 5G

As the demand for faster and more secure communication systems continues to exhibit an exponential growth trend, thanks to the advent of 5G and the ever-increasing number of bandwidth-hungry devices, the development of new high-capacity communication technologies becomes imperative. With optical fiber networks not being of feasible implementation in every scenario, such as in remote locations or low population density areas, Free-Space Optics (FSO) systems appear as a high-throughput, low-cost and secure solution, that can complement traditional fiber-based infrastructures. Infrared FSO communications are a Line-of-sight (LOS) high-capacity optical transmission technology that resorts to the propagation of an optical beam through open air. As open air transmissions lead to atmospheric interactions, the performance of FSO systems suffers from the effects of atmospheric events. This thesis explores the FSO technology as a whole, starting with the characterization of two distinct FSO receiver typologies in terms of misalignment tolerance: i) photodetector-based receivers, in which the FSO signal is directly detected and converted to the electrical domain; and ii) seamless air-to-fiber receivers, in which the interface between wireless and wired media is implemented by an optical fiber collimator, keeping the signal in the optical domain. The impact of channel distortions in an FSO system is also an object of study, with the impact of atmospheric turbulence in an indoor link for Data Center Interconnects (DCI) being assessed through the fitting of the Log-Normal Model. The last section demonstrates the implementation of a 5G-compatible 400 MHz FSO link, with both seamless air-to-fiber and photodetector-based receiver typologies.