Performance of Energy-Harvesting Receivers with Batteries Having Internal Resistance

Modern communication systems will increasingly rely on energy harvested from their environment. Energy harvesting power supplies typically use batteries to store energy and smoothen out the random fluctuation in energy arrivals and have, by nature, an intermittent power profile. This necessitates a rethinking of how we design energy harvesting communication systems, from the viewpoint of both the transmitting device and the destined receiver. Due to the intermittent power profile, both the charge and discharge powers of the battery are more variable and unpredictable than in conventional systems. This impacts the charge and discharge efficiencies when the batteries exhibit non-negligible internal resistance. In this paper, we study the impact of internal resistance at an energy harvesting receiver, that harvests energy both from the received signal and from ambient radio frequency signals. We note that the receiver consumes energy mainly for decoding and model the energy required for decoding as an increasing convex function of the normalized code rate. In this setting, we formulate optimization problems to maximize the amount of information decoded at the receiver. Our study suggests that the internal resistance significantly impacts the design and performance of energy harvesting communication systems and must be taken into account.