Visible Light Communication (VLC) leverages the visible light spectrum to establish wireless communication, offering advantages such as broader bandwidth, and reduced energy consumption compared to traditional radio frequency methods. VLC offers two main approaches: passive and active. Passive VLC takes advantage of sunlight, which is pervasive and highly power-efficient. However, its reliability can be affected by weather conditions and the absence of sunlight at night. On the other hand, active VLC which uses artificial light sources like LEDs, provides more consistent performance but is not power-efficient when sunlight is available. For example, during the day when ample sunlight could be used for passive VLC, turning on a light bulb for active VLC is unnecessary and wasteful.

This thesis tackles these challenges by combining the best of active and passive systems to create an even more power-efficient and reliable system. It addresses two key problems in passive VLC: reducing the power consumption of passive VLC transmitters and enhancing the reliability of passive VLC links through a hybrid system. By replacing the FPGA-based controller with a low-power microcontroller, the power consumption of the Digital Micro-mirror Device used for sunlight modulation was significantly reduced from 1.3W to 36.85mW, while achieving a data rate of 25 kbps with a bit error rate (BER) of less than 1% at a distance of 25 cm. Its maximum range was determined to be 75 cm at 10 kbps. Additionally, integrating an LED component into the passive VLC communication link improved reliability in varying ambient light conditions. The hybrid system demonstrated enhanced performance in low ambient light scenarios, ensuring a BER below 1% regardless of ambient light conditions. In high ambient light scenarios, the LED can be dimmed or turned off, conserving power and making the system more efficient than a purely active VLC system. This thesis contributes to the advancement of energy-efficient and reliable VLC technologies, paving the way for their broader adoption.

Privacy and security are important topics in data aggregation, as companies are aggregating large amounts of sensitive data from their users. The aim of this paper is to improve the security and privacy of data aggregation using smart contracts, homomorphic encryption and post-quantum encryption methods on Hyperledger Fabric. After a literature study, the protocol discussed in \cite{Regueiro2021} was taken as the starting point for an adapted protocol. The adapted protocol is implemented and tested on performance and the security is discussed. The protocol is improved in terms of security by resolving or lowering the chance of security flaws that were present in the protocol in \cite{Regueiro2021}, and introducing post-quantum encryption. However, the adapted protocol in its current implementation is not scalable.