Online Power Control for Block i.i.d. Energy Harvesting Channels

Abstract

We study the problem of online power control for energy harvesting communication nodes with random energy arrivals and a finite battery. The stochastic model for the energy arrivals is block i.i.d., in which the energy arrivals are constant for a fixed duration T, but are independent across different blocks, drawn from an arbitrary distribution. This model can be regarded as a simple approximation to a random process with coherence time T. We propose a simple online power control policy, and prove that its performance gap to the optimal throughput is bounded by a constant which is independent of the parameters of the problem. This also yields a simple formula for the approximately optimal long-term average throughput, which sheds some light on the qualitative behavior of the throughput and how it depends on the ``coherence time'' of the energy arrival process. Our results show that, perhaps counter-intuitively, for a fixed mean energy arrival rate the throughput decreases with increasing coherence time T of the energy arrival process. In particular, the battery size needed to approach the AWGN capacity of the channel increases linearly with the coherence time of the process.