Optimum Transmission Policies for Battery Limited Energy Harvesting Nodes

TLDR

Energy‑harvesting battery‑equipped wireless nodes are emerging as a promising technology for future networks, but their design must account for energy replenishment dynamics and battery storage limits. This study seeks to determine optimal transmission policies for rechargeable nodes, addressing two related optimization problems. The authors formulate the problems under energy‑causality and battery‑capacity constraints, model energy arrivals as discrete packets, derive necessary optimality conditions, and present an algorithm that yields the throughput‑optimal and minimum‑completion‑time policies. They show that the policy maximizing short‑term throughput also solves the minimum‑completion‑time problem, and numerical experiments validate the analytical results.

Abstract

Wireless networks with energy harvesting battery equipped nodes are quickly emerging as a viable option for future wireless networks with extended lifetime. Equally important to their counterpart in the design of energy harvesting radios are the design principles that this new networking paradigm calls for. In particular, unlike wireless networks considered to date, the energy replenishment process and the storage constraints of the rechargeable batteries need to be taken into account in designing efficient transmission strategies. In this work, such transmission policies for rechargeable nodes are considered, and optimum solutions for two related problems are identified. Specifically, the transmission policy that maximizes the short term throughput, i.e., the amount of data transmitted in a finite time horizon is found. In addition, the relation of this optimization problem to another, namely, the minimization of the transmission completion time for a given amount of data is demonstrated, which leads to the solution of the latter as well. The optimum transmission policies are identified under the constraints on energy causality, i.e., energy replenishment process, as well as the energy storage, i.e., battery capacity. For battery replenishment, a model with discrete packets of energy arrivals is considered. The necessary conditions that the throughput-optimal allocation satisfies are derived, and then the algorithm that finds the optimal transmission policy with respect to the short-term throughput and the minimum transmission completion time is given. Numerical results are presented to confirm the analytical findings.