Rafic Hage Chehade

A real-time scheduling framework for embedded systems with environmental energy harvesting

Real-time scheduling refers to the problem in which there is a deadline associated with the execution of a task. In this paper, we address the scheduling problem for a uniprocessor platform that is powered by a renewable energy storage unit and uses a recharging system such as photovoltaic cells. First, we describe our model where two constraints need to be studied: energy and deadlines. Since executing tasks require a certain amount of energy, classical task scheduling like earliest deadline is no longer convenient. We present an on-line scheduling scheme, called earliest deadline with energy guarantee (EDeg), that jointly accounts for characteristics of the energy source, capacity of the energy storage as well as energy consumption of the tasks, and time. In order to demonstrate the benefits of our algorithm, we evaluate it by means of simulation. We show that EDeg outperforms energy non-clairvoyant algorithms in terms of both deadline miss rate and size of the energy storage unit.

A Nonclairvoyant Real-Time Scheduler for Ambient Energy Harvesting Sensors

Ambient energy harvesting also known as energy scavenging is the process where energy is obtained from the environment, converted, and stored to power small devices such as wireless sensors. We present a variant of EDF scheduling algorithm called EH-EDF (Energy Harvesting-Earliest Deadline First). Decisions are taken at run-time without having prior knowledge about the future energy production and task characteristics. We gauge the performance of EH-EDF by means of simulations in order to show its benefits. We evaluate and compare several variants of EH-EDF in terms of percentage of feasible task sets. Metrics such as average length of the idle times are also considered. Simulations tend to demonstrate that no online scheduler can reach optimality in a real-time energy harvesting environment.

Reduction of power field radiation for PLC applications

In this article, we present our investigations on the radiation of the power-line communication (PLC) system. Power line communication or power line carrier is a technology for carrying data on a conductor usually dedicated to electric power transmission. At high frequency, the power lines, whose are dimensioned and adjusted for electrical energy transfer, not to carry high frequency (HF) data signal, act then as radiating antennas.

Study of current distribution over a power cable presenting non-uniform geometry using the partial differential equations approach.

This paper presents a theoretical study of the currents and voltages characteristics transmission over an energy cable (Power Line Transmission PLT). The geometry of line is non-uniform. The proposed approach is based on the Distributed Network model, where the lumped parameters vary as the lines geometry.

Towards multiprocessor scheduling in distributed real-time systems under energy constraints

Performance boosting has been a highly important goal in system designs in the past decades. Not until recently, energy efficiency becomes another critical feature being pursued in a wide variety of products, especially for battery-powered devices. Various studies have been conducted for energy-efficient systems techniques. The most adopted ones are Dynamic Voltage Scaling (DVS) and Dynamic Power Management (DPM). However, all the previous research have disregarded an important aspect of these devices, namely rechargeability of the batteries. Several studies have explored the problem of scheduling real-time tasks in a monoprocessor rechargeable system. This paper summarizes the state-of-art research results of uniprocessor real-time systems under energy constraints. Then, we extend our work to deal with the problem of scheduling real-time tasks in a monoprocessor rechargeable systems.

Partitioned EDF scheduling in multicore systems with quality of service constraints

In this paper we study the partitioned EDF scheduling in a homogeneous multiprocessor environment with Quality of Service (QoS) constraints. The system considered here is a real-time multiprocessor system assumed to be powered by rechargeable batteries. We address the issue of how to best partition a set of firm real-time tasks that can occasionally skip one instance according to a predefined QoS threshold. The main goal is to minimize the energy consumption of the system while offering solutions with respect to transient energy starvation situations the system can experiment. The contribution of the paper is twofold. First, we present a schedulability analysis of firm multiprocessor task sets under QoS constraints. Second we propose new partitionning heuristics integrating skips. The evaluation is conducted from several points of view (minimization of the total processor number, maximization of the spare capacity on each processor).

Stability and Robustness Issues in Real-Time Sustainable Wireless Sensors

In this paper, we address the problem of periodic task scheduling in a sensor node powered with energy harvester. The scheduler can be occasionally forced to skip jobs because of energy shortage or processing overload. Every task executes jobs in conformance with the so-called Skip-Over model where blue jobs may be aborted at any time in contrast to red ones that should complete before deadline. The work presented here aims to consider stability and robustness issues for the Skip-Over model in a uniprocessor energy harvesting system. We present two scheduling strategies, called Green-BWP-LF and Green-BWP-MS specifically adapted to that context. A simulation study shows that these policies outperform the conventional Green-BWP algorithm based on the classical Earliest Deadline rule.

EH-EDF: An on-line scheduler for real-time energy harvesting systems

In this paper, we undertake the problem of on-line real-time scheduling in a uniprocessor platform that is powered by a renewable energy storage unit and uses a recharging system such as photovoltaic cells. Since executing tasks require a certain amount of energy, we must take into account the characteristics of the energy source, capacity of the energy storage as well as energy consumption of the tasks, and time. For this sake, we present a scheduling algorithm called EH — EDF (Energy Harvesting — Earliest Deadline First). In such algorithm, scheduling decisions are taken at run-time without having any prior knowledge about the characteristics of the future energy production and task characteristics.