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Dissertation digest: Designing Scalable yet Energy-Efficient Low-Power Wide-Area Networks
No full textInternational audienceLow-Power Wide-Area Networks (LPWANs) provide connectivity to widely-spread battery-powered devices. In such networks, very large numbers of terminals compete for radio access. Frame collisions naturally occur in the absence of coordination, which is detrimental to network performance. However, each terminal transmits relatively small and sporadic amounts of data. The design of strategies to operate large-scale LPWAN is challenging. In fact, any introduction of protocol overhead for terminal coordination purposes has a detrimental impact on device energy efficiency and ultimately battery life. Herein, this paper summarizes a doctoral thesis [1] focused on the design of scalable yet energy efficient access schemes for LPWAN. One of the key takeaways of this work is the need for dynamic access protocols, capable of adapting their behavior to the traffic load while minimizing the amount of control plane messages. In order to take a step back from the work accomplished, methodological insights about the approaches and performance evaluation tools used during the thesis are also provided. Finally, research perspectives are discussed. More specifically, the application of such schemes to Direct-to-Satellite IoT networks is foreseen as a means to enable worldwide and efficient low-power networks
Achieving reduced latency and energy efficiency in Direct-to-Satellite LoRaWAN communications
No full textInternational audienceDirect-to-satellite (DtS) communications are becoming increasingly popular in the field of connected objects, since Low Earth Orbit (LEO) satellites can be easily deployed at lower and lower costs. In fact, a DtS Internet of Things (IoT) paves the way for the development of an incredibly vast gamut of monitoring applications for very inaccessible areas, e.g., oceans, mountains, and deserts. In this context, the medium access protocol used for Long Range Wide Area Network (LoRaWAN) has recently been proposed as a viable solution for policing the communication between ground low power devices and LEO satellites equipped with LoRaWAN gateways. However, the default LoRaWAN medium access scheme is based on a "transmit first" policy that inevitably augments the collision rate among the increased number of concurrent devices in the satellite coverage. Instead, this paper focuses on a "listen first" policy enabled through LoRaWAN Class B beacons and the sole adoption of Activation-By-Personalization (ABP). In more detail, a wake-up strategy allowing ground LoRaWAN devices to intermittently switch on and off their own radio for listening to incoming beacons is studied and analyzed through simulations. By means of this investigation, it is possible to find the best timer settings guaranteeing a good compromise between energy saving and the need to reduce the time to catch the first beacon. Some preliminary results related to the availability of a single LoRaWAN-enabled LEO satellite show that a reduction of 33% in energy consumption can be achieved at the cost of a slightly increased "first catch" time
Neural Network-Based Estimation of Optical Feedback Factor in Self-Mixing Interferometry Systems across various feedback regimes
No full textInternational audienceSelf-mixing interferometry (SMI) system is a promising and low-cost approach for displacement measurements. The resolution and precision of displacement estimation depend on key parameters of the SMI system and, in particular, on the optical feedback factor (C). This article presents a new method for estimating this C factor based on an artificial neural network (ANN) that analyzes certain specific fringe shape features of SMI signals. Specifically, only six features of the SMI signal are taken into account as input to a compact neural network with one hidden neuron layer (14 neurons) by the estimation process, which reduces the computational cost and simplifies its deployment. This study evaluates the C-estimation capability of the method in various simulated and experimental scenarios, including variations in displacement amplitude and frequency, random displacements, noise levels, and speckle effects. These analyses show that the method works correctly for a moderate feedback regime ( 14.6 ), this error is less than 2% (for C<8 ). Comparisons with other methods show similar or better accuracy but with the advantage of being able to handle all displacement waveforms (sinusoidal or arbitrary) at low computational cost, which facilitates integration into a real-time embedded system
Evolution of Measures in Nonsmooth Dynamical Systems: Formalisms and Computation
No full textInternational audienceThis article develops mathematical formalisms and provides numerical methods for studying the evolution of measures in nonsmooth dynamical systems using the continuity equation. The nonsmooth dynamical system is described by an evolution variational inequality and we derive the continuity equation associated with this system class using three different formalisms. The first formalism consists of using the {superposition principle} to describe the continuity equation for a measure that disintegrates into a probability measure supported on the set of vector fields and another measure representing the distribution of system trajectories at each time instant. The second formalism is based on the regularization of the nonsmooth vector field and describing the measure as the limit of a sequence of measures associated with the regularization parameter. In doing so, we obtain quantitative bounds on the Wasserstein metric between measure solutions of the regularized vector field and the limiting measure associated with the nonsmooth vector field. The third formalism uses a time-stepping algorithm to model a time-discretized evolution of the measures and show that the absolutely continuous trajectories associated with the continuity equation are recovered in the limit as the sampling time goes to zero. We also validate each formalism with numerical examples. For the first formalism, we use polynomial optimization techniques and the moment-SOS hierarchy to obtain approximate moments of the measures. For the second formalism, we illustrate the bounds on the Wasserstein metric for an academic example for which the closed-form expression of the Wasserstein metric can be calculated. For the third formalism, we illustrate the time-stepping based algorithm for measure evolution on an example that shows the effect of the concentration of measures
Isolation of adipose stromal cells from blood using a two-step microfluidic platform ASCfinder
No full textInternational audienceMesenchymal stromal cells (MSCs) hold significant promise for their therapeutic potential and their possible role as disease biomarkers. While evidence suggests the presence of circulating Adipose-derived MSC (ASC) in peripheral blood (PB), isolating them is particularly challenging due to their low abundance, size variability, and incomplete characterization of their native immunophenotype in PB. Consequently, the relationship between ASC frequency in blood and various physiological or pathological conditions has been underexplored. In this study, we introduce ASC-Finder, a label-free isolation method specifically designed for adipose stromal cells (ASCs), a key MSC population. ASC-Finder integrates two independent modules: a size-dependent hydrodynamic filtration unit for sorting erythrocytes directly from PB and a negative enrichment module based on immunological markers to deplete remaining leukocytes. The device enabled removal of 99.98% of erythrocytes while achieving high recovery rates of spiked ASCs (> 81%) at rare-event concentrations (< 100 ASC/mL blood). Remarkably, ASC-Finder operates without clogging, even after multiple runs with donor blood samples. Crucially, our method bypasses the need for harsh lysis, centrifugation, or dilution buffers, preserving both cell integrity and phenotype—key factors for the discovery of novel cellular events. This work represents a significant advancement in the direct enrichment of circulating ASCs from whole PB without cell lysis, offering a crucial step toward investigating the characterization and role of blood-circulating ASCs
Disjunctive Scheduling in Tempo
No full textInternational audienceIn this paper we introduce a constraint programming lazy clause and literal generation solver embarking ideas from SAT Modulo theories. A key aspect of the solver are Boolean variables with an associated semantic in difference logic, i.e., systems of binary numeric difference constraints or edges, making it particularly adapted to scheduling and other temporal problems. We apply this solver to disjunctive scheduling problems, where edges are used as branching variables, can be inferred via the edge finding rule as well as by transitivity reasoning, and can in turn strengthen propagation via temporal graph reasoning. Our experiments on job-shop scheduling show that a deep integration of these techniques makes our solver competitive with state-of-the-art approaches on these problems
Exact algorithms in bar nesting: How to cut general items from linear stocks so that wastage is minimised
No full textInternational audienceThis paper proposes exact, polynomial-time algorithms that solve the problem of cutting items with angled sides from a single linear stock so that wastage is minimised. In industry, this problem is called ''bar nesting''. Here we give an algorithmic framework that solves several important variants of the problem, including cutting items from stocks with asymmetric cross-sections, cutting items whose sides occur on different planes, and the minimum score separation problem
Réseaux de Petri : Théorie et mise en oeuvre
No full textInternational audienceIn diesem Artikel werden die formalen und anwendungsbezogenen Aspekte von Petri-Netzen (RdP) vorgestellt. Dabei handelt es sich um ein Werkzeug zur Modellierung und Analyse von Systemen in Form von Zuständen, Übergängen und Token, in denen sich die Kontrolle asynchron und gleichzeitig entwickelt. Das Konzept der Token wird zur Darstellung der Kapazität verwendet. Es werden verschiedene Erweiterungen von RdP diskutiert, die eine größere funktionale Ausdruckskraft und eine kompaktere Modellierung bieten. Eine andere Art von Erweiterungen beinhaltet die Einbeziehung der Zeit. Diese Erweiterungen ermöglichen die Einführung von Begriffen wie Dringlichkeit, Watchdog und Dauer. Schließlich wird eine Reihe von Anwendungswerkzeugen für die Modellierung, Simulation und Codegenerierung vorgestellt.This article presents the formal and applicative aspects of Petri nets (RdP). This is a tool for modeling and analyzing systems in the form of states, transitions and tokens, in which control evolves asynchronously and concurrently. The concept of to- ken is used to represent capacity. Various extensions to RdP are discussed, offering greater functional expressiveness and more compact modeling. Another type of exten- sion involves the incorporation of time. These extensions make it possible to introduce the notions of urgency, watchdog and duration. Finally, a set of application tools is presented for modeling, simulation and code generation.Cet article présente les aspects formels et applicatifs des réseaux de Petri. C'est un outil qui permet de modéliser et d'analyser des systèmes sous forme d'états, de transitions et de jetons dans lequel l'évolution du contrôle se fait de manière asynchrone et concurrente. La notion de jeton permet de modéliser le concept de capacité. Différentes extensions de RdP sont détaillées, offrant une expressivité fonctionnelle accrue et proposant des modélisations plus compactes. Un autre type d'extension concerne l'introduction du temps. Ces extensions permettent d'introduire les notions d'urgence, de chien de garde et de durée. Enfin un ensemble d'outils applicatifs sont détaillés pour la modélisation, la simulation et la génération de code