Optimal policies for two-user energy harvesting device networks with imperfect state-of-charge knowledge

Energy Harvesting Devices (EHDs) are enjoying continuously increasing popularity in Wireless Sensor Network research, due to their ability to “harvest” energy from the environment, thus allowing long-term and autonomous operation. Traditional approaches generally assume that the exact energy value of the State-of-Charge (SOC) of an EHD is known. In reality, batteries are practically composed by electro-chemical rechargeable elements or super-capacitors, where the estimation of the energy levels is a complex task. In this paper, we analyze operation policies able to maximize the long-term reward for a network consisting of a pair of EHDs and a central controller (CC), under imperfect knowledge of the SOC. More precisely, we suppose that the CC only knows whether each EHD is “LOW” or ”HIGH,”and has to determine the amount of energy devoted to the transmission over a shared wireless channel. We show that the performance degradation due to the imperfect knowledge of the SOC decreases with the battery capacity of the two nodes, and is practically negligible when this value is sufficiently high.