E-WAN: Efficient Communication in Energy Harvesting Low-Power Networks

The ever-increasing number of distributed embedded systems in the context of the Internet of Things (IoT), Wireless Sensor Networks (WSN), and Cyber-Physical Systems (CPS) rely on wireless communication to collect and exchange data. Nodes can employ single-hop communication which, despite its ease, may necessitate energy-intensive long-range communication to cover long distances. Conversely, multi-hop communication allows for more energy-efficient short-range communication since nodes can rely on other nodes to forward their data. Yet, this approach requires relay nodes to be available and continuous maintenance of a dynamically changing distributed state. At the same time, energy harvesting has the potential to outperform traditional battery-based systems by improving their lifetime, scalability with lower maintenance costs, and environmental impact. However, the limited and temporally and spatially variable harvested energy poses significant challenges for networking in energy harvesting networks, particularly considering the energy demands and characteristics of both multi-hop and single-hop communication. We propose E-WAN, a protocol for energy harvesting wide-area low-power networks that builds on the concept of \emph{virtual sub-networks} to enable resource-efficient multi-hop communication when possible and reliable however energy-intensive point-to-point communication otherwise. Nodes autonomously and dynamically move between the two and adjust to changing network states and resources based only on easily obtainable network state information. We illustrate E-WAN's advantages both in terms of efficiency and adaptability in various communication and harvesting scenarios. Furthermore, we demonstrate E-WAN operating in a realistic setting by deploying an energy harvesting network in a real-world indoor environment.