Feasibility analysis of periodic real-time systems with energy harvesting capabilities

Abstract

Energy harvesting now appears as a feasible solution to power wireless devices. Such ones including sensor nodes have to be energy neutral i.e. be able to never consume more energy than available. Energy can be drawn from many ambient sources including solar, vibration, etc. Most of wireless devices perform periodic sampling and computations using a microprocessor for real-time monitoring. The software tasks that typically take place in these systems are time critical and cyclic with specified deadlines attached to finishing times. In this paper, we explore the problem of feasibility analysis of hard real-time periodic task sets on a single processor powered by renewable energy. Firstly, we investigate the notion of robustness as the capability of the system to remain stable even in case of positive changes in its operating environment. We prove that our feasibility test is robust with respect to the profile of the energy source. Secondly, we prove that for asynchronous tasks whose initial release times are not known in advance, feasibility can be checked considering the synchronous activation pattern which corresponds to the worst-case scenario. Finally, whenever accurate prediction of the incoming environmental energy is impossible, a sufficient feasibility test with high implementation efficiency is proposed.