EH-CRAM: A Sustainable Energy Harvesting Algorithm for LPWANs

Low Power Wide Area Network (LPWAN) technologies offer the advantage of wide coverage areas and low power consumption for low data-rate Internet-of-Things (IoT) applications. LoRaWAN, the Long Range Wide Area Network is a key technology in this space, with a growing worldwide presence. LoRa devices are expected to operate autonomously for extended periods in order to support diverse IoT applications. Despite being energy efficient, frequent battery replacements are typically required over the lifetime of a LoRa device. This increases maintenance costs and furthermore, disposing of large numbers of dead batteries is damaging to the environment. Energy harvesting offers a potential solution, but it is difficult to ensure sustainability. In this paper, we propose EH-CRAM, a centralised Kalman filter-based optimisation algorithm where the gateway is responsible for controlling End-Device configurations (i.e: data transmission rates, spreading factors and energy harvesting period) based upon incoming traffic and solar energy, thus balancing energy supply and demand. In addition, by using a time-synchronised cryptographic frequency hopping scheme, EH-CRAM also tackles the issues of energy efficiency and performance. Our evaluation shows that EH-CRAM significantly reduces contention, while maximising reliability and energy efficiency to support sustainable energy-harvesting for LoRa EndDevices (ED's).