This thesis focuses on identifying, investigating, and addressing three main limitations of LiFi systems in a typical indoor scenario. First, this thesis addresses the backhaul connectivity of the LiFi Access Points (AP) to the Internet. Current backhaul solutions for LiFi networks face practical limitations, especially for battery-free IoT applications. To fill this gap, the thesis proposes LoW-Fi. This novel downlink backhaul solution reuses the existing lighting and WiFi infrastructure to ensure the scalability, flexibility, and low power consumption required by battery-free IoT deployments. Then, this thesis proposes a comprehensive and bi-directional system architecture, integrating LoW-Fi for downlink and PassiveLiFi RF backscatter system for uplink. This results in a novel network architecture suitable for applications like precision agriculture. The proposed solutions were implemented and tested in a real greenhouse applications scenario. Second, this thesis targets the dimming problem in LiFi networks. Domming is the functionality of LiFi systems that allows users to adapt the illumination conditions to their eye comfort without compromising the LiFi communication performance. Existing dimming schemes for LiFi networks have many drawbacks, including limited precision on the adjustment of the dimming level, constrained dimming range, and high complexity. The thesis presents a novel modulation and dimming scheme that addresses such limitations by operating in both VL and IR bands, maintaining good communication performance even under extreme illumination conditions. Additionally, the thesis tackles the handover decision-making problem in hybrid LiFi and WiFi networks, introducing RL-HO, a handover algorithm leveraging machine learning techniques to optimize handover rate and average throughput. Overall, this thesis contributes practical solutions to enhance the performance and applicability of LiFi technology in real scenarios, addressing critical challenges for its widespread adoption.

About Dayrene Frómeta

Dayrene Frómeta is a Ph.D. candidate of the Pervasive Wireless Systems Group at IMDEA Networks Institute since July 2020. She worked as a lecturer in the department of Telematics in the University of Havana José Antonio. Her current main research is working as an Early Stage Researcher on Marie-Curie ITN project: Enlightem. This project focuses on low energy VLC systems for the IoT. Her research targets a topic which is how to provide backhaul connectivity to hundreds or thousands of VLC Aps under dense VLC deployments of the IoT.

PhD Thesis Advisor: Dr. Domenico Giustiniano and Dr. Borja Genovés Guzmán, IMDEA Networks Institute, Spain

University: University Carlos III of Madrid, Spain

Doctoral Program: Telematic Engineering

PhD Committee members:

• President: Marco Antonio Zúñiga Zamalloa, Professor, Delft University of Technology (TU Delft)
• Secretary: Ana García Armada, Researher, Carlos III University, Madrid, Spain
• Panel member: Victor Guerra Yánez, Researcher, Pi Lighting Sarl, R&D company, Switzerland