Energy Neutral User Equipment : powering cellular IoT applications using energy harvesting

Abstract: With the rise in the number of Internet of Things (IoT) applications, there is also an increase in the number of batteries being used to power these connected devices. The lifespan of IoT devices is usually limited by how long their batteries last. In some situations the maintenance cost of replacing the batteries can make these applications economically non-viable, while for others could mean having to replace (after a few years) thousands or millions of small batteries in massively deployed systems. Apart from the economic impact, the later could also bring with it a serious environmental impact associated to the production and (lack of) recycling of the batteries. To reduce the dependence on battery lifespan, alternative ways of supplying the energy needs of the IoT devices need to be explored. One possibility is to use energy harvesting, taking advantage of existent environmental energy to power the IoT devices, potentially allowing for long operating lifespan with a limited (or none) use of batteries. This concept of an autonomous powered and internet connected system is what defines the idea of the Energy Neutral User Equipment (UE). This thesis experimentally approaches the design of such an Energy Neutral UE system by implementing a typical asset tracker IoT application, focusing in the use of cellular Low Power Wide Area Networks (LPWAN) for communications, and in the development of a suitable energy harvesting solution using only Commercial-Off-The-Shelf (COTS) components. To implement such a system, the operating characteristics and power consumption of the LTE-M and NB-IoT LPWANs were studied, alongside with the selected energy harvesting devices for vibration and solar energy, and the characteristics of the asset tracking application. All of this led to the development of a complete autonomous system built using the nRF9160 System in Package as UE. The experiments showed that the implemented Energy Neutral UE is able to obtain and transmit location information at short intervals using only the energy harvested from ambient vibrations and light radiation, while only having a relatively small supercapacitor as energy storage.