A Battery Lifespan-Aware Protocol for LPWAN

Energy harvesting sources, such as solar, wind, or vibration, combined with rechargeable batteries, are a promising way to power Low-Power Wide-Area Network (LPWAN) devices to reduce the cost and frequency of redeploying single-use batteries. However, being oblivious to the usage of rechargeable batteries can severely reduce their capacity to store energy, which is also known as the battery lifespan. Existing energy-aware protocols mostly focus on network lifetime and pay little attention to maximizing the battery lifespan of network nodes while the latter can directly help reduce battery waste and enhance environmental sustainability. In this paper, we propose the first Media Access Control (MAC) protocol to maximize the minimum battery lifespan among all nodes in an LPWAN based on LoRa. Our approach differs from traditional objectives focusing on min-imizing energy consumption or maximizing network lifetime as they may not necessarily maximize battery lifespan. The proposed MAC protocol leverages the concept of software-defined batteries to regulate the energy stored and consumed by each node's battery based on estimated energy requirements, green energy generation, and changes in data utility. To limit the degradation of battery capacity due to continuous charging/discharging, the underpinning idea is to determine an appropriate time for each transmission considering its impact on battery degradation while also minimizing the impact on data utility. Furthermore, the energy stored in each battery is limited to reduce calendar aging, the natural degradation of battery capacity over time. The proposed protocol is local, online, and asynchronous, and incurs low overhead. We evaluate our approach through experiments on a LoRa network and large-scale simulations in NS-3. The experiments show that the proposed MAC protocol improves battery lifespan by up to 69.7% and data utility by up to 39% in a current LoRa network while incurring a CPU utilization overhead of only 12 % at each LoRa node.