Batteryless NB-IoT prototype for bidirectional communication powered by ambient light?

IoT use-cases aim to provide high-quality services where IoT infrastructures are always linked with the Internet. They require large scale deployment of small devices acting as sensors and actuators in different places. These devices need to be energy efficient and run sustainably. The maintenance of such large scale devices is difficult if they are powered by batteries that need to be replaced after some time. Moreover, disposing of these batteries also pollutes the soil and contaminates groundwater. Narrowband IoT (NB-IoT) is one of the long-range technologies that supports connectivity even in deep indoor closed areas such as underground parking lots, elevators, and tunnels. Therefore, in this article, the suitability of an NB-IoT device or User Equipment (UE) to be powered without any batteries to enable a long-term sustainable maintenance-free IoT network is demonstrated. We develop a prototype using a small photovoltaic solar panel for indoor light harvesting using sunlight or an artificial light bulb to power the NB-IoT UE. Due to the unpredictability of energy harvesting, the batteryless UE can experience frequent switches between the ON and OFF states. Therefore, we evaluate the performance of the solution where the UE communicates either uni-(uplink only) or bi-directionally (uplink and downlink) for different capacitor sizes at different artificial light intensities. We also evaluate the solution under dynamic harvesting power using natural light during daytime. The experimental results conclude that the batteryless NB-IoT UE supports a transmission interval of 60 s without experiencing any restarts when harvesting 6 mW or more, which can be harvested by placing a 6 W artificial light bulb at a distance of 60 cm or less.