Analysis and Design of Finite Alphabet Iterative Decoders Robust to Faulty Hardware

This paper addresses the problem of designing LDPC decoders robust to transient errors introduced by a faulty hardware. We assume that the faulty hardware introduces errors during the message passing updates and we propose a general framework for the definition of the message update faulty functions. Within this framework, we define symmetry conditions for the faulty functions, and derive two simple error models used in the analysis. With this analysis, we propose a new interpretation of the functional Density Evolution threshold previously introduced, and show its limitations in case of highly unreliable hardware. However, we show that under restricted decoder noise conditions, the functional threshold can be used to predict the convergence behavior of FAIDs under faulty hardware. In particular, we reveal the existence of robust and non-robust FAIDs and propose a framework for the design of robust decoders. We finally illustrate robust and non-robust decoders behaviors of finite length codes using Monte Carlo simulations.Comment: 30 pages, submitted to IEEE Transactions on Communication

Density Evolution and Functional Threshold for the Noisy Min-Sum Decoder

This paper investigates the behavior of the Min-Sum decoder running on noisy devices. The aim is to evaluate the robustness of the decoder in the presence of computation noise, e.g. due to faulty logic in the processing units, which represents a new source of errors that may occur during the decoding process. To this end, we first introduce probabilistic models for the arithmetic and logic units of the the finite-precision Min-Sum decoder, and then carry out the density evolution analysis of the noisy Min-Sum decoder. We show that in some particular cases, the noise introduced by the device can help the Min-Sum decoder to escape from fixed points attractors, and may actually result in an increased correction capacity with respect to the noiseless decoder. We also reveal the existence of a specific threshold phenomenon, referred to as functional threshold. The behavior of the noisy decoder is demonstrated in the asymptotic limit of the code-length -- by using "noisy" density evolution equations -- and it is also verified in the finite-length case by Monte-Carlo simulation.Comment: 46 pages (draft version); extended version of the paper with same title, submitted to IEEE Transactions on Communication

Density Evolution for the Design of Non-Binary Low Density Parity Check Codes for Slepian-Wolf Coding

International audienceIn this paper, we investigate the problem of designing good non-binary LDPC codes for Slepian-Wolf coding. The design method is based on Density Evolution which gives the asymptotic error probability of the decoder for given code degree distributions. Density Evolution was originally introduced for channel coding under the assumption that the channel is symmetric. In Slepian-Wolf coding, the correlation channel is not necessarily symmetric and the source distribution has to be taken into account. In this paper, we express the non-binary Density Evolution recursion for Slepian-Wolf coding. From Density Evolution, we then perform code degree distribution optimization using an optimization algorithm called differential evolution. Both asymptotic performance evaluation and finite-length simulations show the gain at considering optimized degree distributions for SW coding

Toxicity of pesticides, singly and in mixtures, towards marine microalgae and oyster larvae : approach combining laboratory micro-bioassays with the use of POCIS passive sampler extracts

La viticulture génère un potentiel risque de toxicité pour les écosystèmes aquatiques. Dans ce contexte, cette thèse visait à : i) effectuer le screening de toxicité de pesticideschoisis sur des microalgues marines et la larve d’huître creuse ; ii) évaluer la toxicité de mélanges binaires de pesticides sur des microalgues marines via des approches demodélisation ; iii) comparer la toxicité de mélanges complexes issus de l’environnement d’étude par l’utilisation d’extraits d’échantillonneurs passifs de type POCIS. Des POCIS ont été déployés mensuellement, d’une part pour évaluer la contamination chimique du bassin versant expérimental de Marcillac (Gironde, France), d’autre part afin de les extraire pour en étudier le potentiel toxique. Les extraits constituaient un mélange complexe représentatif de la contamination chimique pour la station/période suivie. Un test de toxicité en microplaques a été optimisé pour permettre de répondre aux différents objectifs identifiés. Deux fongicides et un insecticide ont induit une très forte toxicité pour les larves d'huître. Deux herbicides et un fongicide ont induit une toxicité importante pour les microalgues testées. Des interactions additives, antagonistes et synergiques ont pu être mises en évidence. Les effets de ces mélanges sur la physiologie des microalgues étudiées ont également été évalués. Les extraits de POCIS ont induit une toxicité significative et variable en fonction des stations et périodes suivies. Les résultats obtenus au cours de cette thèse contribuent à améliorer nos connaissances sur les potentiels effets toxiques associés au transfert des pesticides issus de la viticulture vers les milieux aquatiques.Viticulture is responsible for a potential toxicity risk towards aquatic ecosystems. In this context, this thesis aimed to: i) perform a toxicity screening of chosen pesticidestowards marine microalgae and oyster larvae; ii) evaluate the toxicity of pesticides binary mixtures on marine microalgae using modelling approaches; iii) compare the toxicityof complex mixtures from the study site using POCIS passive sampler extracts. POCIS were deployed monthly, firstly to evaluate the chemical contamination of theexperimental watershed of Marcillac (Gironde, France), secondly in order to study the toxic potential of the extracts. The extracts constituted in a complex mixturerepresentative of the chemical contamination for the followed station/period. A toxicity test using microplates was optimized to meet the identified objectives. Two fungicidesand one insecticide induced a very strong toxicity for oyster larvae. Two herbicides and one fungicide induced a significant toxicity for the tested microalgae. Additive,antagonistic and synergistic interactions were highlighted. Effects of these mixtures on the physiology of the studied microalgae were also evaluated. POCIS extracts induceda significant toxicity that varied depending on the stations and periods considered. Results obtained during this thesis contributed to improve our knowledge towards thepotential toxic effects associated with the transfer of pesticides used in viticulture towards aquatic environments

Finite Alphabet Iterative Decoders Robust to Faulty Hardware: Analysis and Selection

Abstract-In this paper, we analyze Finite Alphabet Iterative Decoders (FAIDs) running on faulty hardware. Under symmetric error models at the message level, we derive the noisy Density Evolution equations, and introduce a new noisy threshold phenomenon (called functional threshold), which accurately characterizes the convergence behavior of LDPC code ensembles under noisy-FAID decoding. The proposed functional threshold is then used to identify FAIDs which are particularly robust to the transient hardware noise. Finite-length simulations are drawn to verify the validity of the asymptotical study

Finite alphabet iterative decoders robust to faulty hardware: Analysis and selection

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Outil de la valorisation des données de l’environnement littoral pour la Directive Cadre Européenne sur l’eau (DCE). Atlas en ligne interactif : présentation de l’outil, fonctionnement du module d’administration

La diffusion et la valorisation des résultats des suivis DCE passe notamment par la mise en ligne des informations régulièrement mises à jour concernant les réseaux de surveillance, les masses d’eau et les résultats de la surveillance. L’outil spécifiquement dédié à ces mises à jour a été développé par la société Alkante. Les instructions pour l’utilisation de cet outil dans chaque bassin, remises à jour des évolutions de 2014, sont présentées ici

Toxicity of binary mixtures of pesticides to the marine microalgae Tisochrysis lutea and Skeletonema marinoi: Substance interactions and physiological impacts

This study screened binary mixtures of pesticides for potential synergistic interaction effects on growth of the marine microalgae Tisochrysis lutea and Skeletonema marinoi. It also examined the single and combined effects of three of the most toxic substances on microalgal physiology. Single substances were first tested on each microalgal species to determine their respective EC50 and concentration-response relationships. The toxicity of six and seven binary mixtures was then evaluated in microplate experiments on the growth of T. lutea and S. marinoi, respectively, using two mixture modelling approaches: isobolograms and the MIXTOX tool, based on Concentration Addition (CA) or Independent Action (IA) models. Significant cases of antagonism (for both species) and synergism (for S. marinoi) were observed for the mixtures of isoproturon and spiroxamine, and isoproturon and metazachlor, respectively. These two mixtures, together with that of isoproturon and diuron, for which additivity was observed, were further studied for their impacts on the physiology of each species. Exposures were thus made in culture flasks at three concentrations, or concentration combinations for mixtures, selected to cause 25%, 50% and 75% growth rate inhibition. The effects of the selected pesticides singly and in combination were evaluated at three perceived effect concentrations on esterase metabolic activity, relative lipid content, cytoplasmic membrane potential and reactive oxygen species (ROS) content by flow cytometry, and on photosynthetic quantum yield (ϕ’M) by PAM-fluorescence. Isoproturon and diuron singly and in mixtures induced 20–40% decreases in ϕ’M which was in turn responsible for a significant decrease in relative lipid content for both species. Spiroxamine and metazachlor were individually responsible for an increase in relative lipid content (up to nearly 300% for metazachlor on S. marinoi), as well as cell depolarization and increased ROS content. The mixture of isoproturon and metazachlor tested on S. marinoi caused a 28–34% decrease in ϕ’M that was significantly higher than levels induced by each of substances when tested alone. This strong decrease in ϕ’M could be due to a combined effect of these substances on the photosynthetic apparatus, which is likely the cause of the synergy found for this mixture