Title: Energy Harvesting Communication Using Finite-Capacity Batteries with Internal Resistance,
Abstract: Modern systems will increasingly rely on energy harvested from their
environment. Such systems utilize batteries to smoothen out the random
fluctuations in harvested energy. These fluctuations induce highly variable
battery charge and discharge rates, which affect the efficiencies of practical
batteries that typically have non-zero internal resistances. In this paper, we
study an energy harvesting communication system using a finite battery with
non-zero internal resistance. We adopt a dual-path architecture, in which
harvested energy can be directly used, or stored and then used. In a frame,
both time and power can be split between energy storage and data transmission.
For a single frame, we derive an analytical expression for the rate optimal
time and power splitting ratios between harvesting energy and transmitting
data. We then optimize the time and power splitting ratios for a group of
frames, assuming non-causal knowledge of harvested power and fading channel
gains, by giving an approximate solution. When only the statistics of the
energy arrivals and channel gains are known, we derive a dynamic programming
based policy and, propose three sub-optimal policies, which are shown to
perform competitively. In summary, our study suggests that battery internal
resistance significantly impacts the design and performance of energy
harvesting communication systems and must be taken into account.