First of all, we identified the materials that can perform as RIS: metasurfaces and mirrors. We first evaluated the placement of mirrors to minimize the outage area, which is the key performance metric for IoT devices. This contribution was published in the flagship conference IEEE Globecom 2023.
We extended the first contribution with the introduction of movable mirrors. We studied the specular and diffuse reflections of mirrors and wall elements, and we formulated an optimization problem to minimize the outage probability while minimizing one of the two available resources, the number of mirrors and the total optical power allocated among LEDs. This work was published in IEEE Transactions on Wireless Communications. Then, we studied the performance of ORIS in a multi-user scenario to minimize the outage probability, and it was published in IEEE Photonics Technology Letters.
The third main contribution was published in IEEE Globecom 2024, where we studied the potential of curved mirrors as static reflective surfaces to provide a broadening specular reflection that increases the signal coverage in mirror-assisted VLC scenarios.
The study of ORIS was combined with angle diversity receivers, and it was discovered that both must coexist as they complement and enable each other. This work was published in IEEE Globecom 2025.
Finally, the autonomy of IoT devices has been studied together with their communication performance. We introduced, for the first time, the Maximum Communication Point (MCP), a new operating point that complements the traditional Maximum Power Point (MPP) by optimizing communication performance. This was published in IEEE Transactions on Communications.
Note that these contributions contributed to the achievement of the objectives O1, O2, O3 and O4.
Additionally, in line with the evolving horizon of RISA-VLC’s research, we have performed the following activities:
We studied multi-chip LEDs to increase the data rate and energy harvested. In this context, we derived an exact closed-form procedure for the allocation of power per individual LED chip for any tri-color combination, which is beyond the state of art, and we evaluated communication and illumination metrics for multiple LED combinations. This contribution was published in the IEEE/Optica Journal of Lightwave Technology.
Besides, the usage of RGB LEDs was extended to vehicular scenarios that call for high data rates and low latencies. We proposed a novel transmission scheme referred to as colored blind interference alignment (cBIA), and it was published in IEEE Transactions on Vehicular Technology.
Still working on the transmitter side, we evaluated the communication and energy harvesting performance in dimming mode, which was published in Computer Communications journal. Besides, we studied the performance of low-power metasurfaces installed at the transmitter to modulate sunlight and increase the spectral efficiency. This contribution was published in the conference MedComNet 2023.
Looking at the autonomy performance of the IoT device, we proposed a system architecture for battery-free IoT systems, that was published in IEEE ICNP 2023. Additionally, a demonstration for a battery-free LiFi-based IoT device was presented in ACM Mobicom 2023.
Note that these last works contributed to attaining the objective O4 of RISA-VLC.
Finally, RISA-VLC went beyond the planned activities and studied the performance of LiFi, which is the core technology of the project, together with other widespread RF systems such as WiFi. We have designed a classification model to predict the type of user’s trajectory and assist a reinforcement learning algorithm to make handover decisions that are automatically adapted to new network conditions. This work was published in the IEEE/Optica Journal of Optical Communications and Networking.
