Réduction de la Complexité du Décodeur Sphérique grâce à l'Adaptation de la Décomposition QR

National audienceL'objet de cet article est de présenter une nouvelle technique de détection, le décodeur sphérique, qui utilise une Décomposition QR. Dans cet article, la Décomposition QR de Householder, qui permet d'obtenir des coefficients réels positifs sur la diagonale de R, est étudiée, alors que l'approche usuelle emploie la Décomposition QR de Gram Schmidt. Même si cette modification provoque une augmentation de la complexité des calculs de la Décomposition QR par rapport à la technique existante, elle permet de réduire fortement la complexité du Décodeur Sphérique adapté, de telle sorte que la complexité globale est réduite. L'objectif de l'étude est de quantifier la diminution de la complexité globale dans un contexte Long Term Evolution (LTE), le protocole utilisé pour la quatrième génération de téléphones portables, sur une cible Embedded Vector Processor (EVP)

Complexity gain of QR Decomposition based Sphere Decoder in LTE receivers

ISBN: 978-1-4244-2515-0International audienceIt has been widely shown that the Sphere Decoding can be used to find the Maximum Likelihood (ML) solution with an expected complexity that is roughly cubic in the dimensions of the problem. However, the computational complexity becomes prohibitive if the Signal-to-Noise Ratio is too low and/or if the dimension of the problem is too large. That is why another technique denoted as Fixed-complexity Sphere Decoder (FSD) is an interesting approach. This algorithm needs a preprocessing step, and in this paper the QR-Decomposition-based preprocessing technique, which is not inconsequential, will be studied. Two different techniques are exposed, including the classical Gram Schmidt orthonormalization process. Their computational complexities and their impacts on the FSD computational complexity are studied. In the LTE context, the overall computational complexities of the two detection techniques are quantified and are shown to be dependent on the constellation size

Turbulent Couette-Taylor flows with endwall effects: a numerical benchmark

International audienceThe accurate prediction of fluid flow within rotating systems has a primary role for the reliability and performance of rotating machineries. The selection of a suitable model to account for the effects of turbulence on such complex flows remains an open issue in the literature. This paper reports a numerical benchmark of different approaches available within commercial CFD solvers together with results obtained by means of in-house developed or open-source available research codes exploiting a suitable Reynolds Stress Model (RSM) closure, Large Eddy Simulation (LES) and a direct numerical simulation (DNS). The predictions are compared to the experimental data of Burin et al. (2010) in an original enclosed Couette-Taylor apparatus with endcap rings. The results are discussed in details for both the mean and turbulent fields. A particular attention has been turned to the scaling of the turbulent angular momentum G with the Reynolds number Re. By DNS, G is found to be proportional to Rea, the exponent a = 1.9 being constant in our case for the whole range of Reynolds numbers. Most of the approaches predict quite well the good trends apart from the k-w SST model, which provides relatively poor agreement with the experiments even for the mean tangential velocity profile. Among the RANS models, even though no approach appears to be fully satisfactory, the RSM closure offers the best overall agreement

Analysis of TerraSAR-X data and their sensitivity to soil surface parameters over bare agricultural fields

International audienceCette recherche a pour objectif de mettre en évidence la contribution des capteurs haute résolution pour une meilleure caractérisation de la surface du sol et pour analyser les effets de la polarisation et de l'angle d'incidence radar. L'objectif de cet article est d'analyser la sensibilité des données haute résolution Terrassar-X sur des sols sans couverture végétale et d'étudier la variabilité spatiale. Les relations entre le coefficient de rétrodiffusion et les paramètres du sol seront étudiés grâce aux images (TerraSAR, Ikonos, SPOT) ainsi que grâce aux mesures de terrain recueillies pendant plusieurs campagnes de terrain en hiver et printemps 2008-2009. Ce travail a été mené sur le bassin de l'Orgeval (France). / Our research aims to show the contribution of high resolution spatial sensors for a better characterization of soil surface, and to analyze polarization effects and radar incidence angle. The objective of this paper is to analyze the sensitivity of very high resolution TerraSAR-X radar data taken over bare soils, and to study the spatial variability. The relationship between backscattering coefficient and soil's parameters (moisture, surface roughness, and texture) will be examined by means of satellite images (TerraSAR, Ikonos, SPOT), as well as ground truth measurements, recorded during several field campaigns in the winter and spring of 2008 and 2009. This study is carried out on Orgeval catchment (France)

Transferts de chaleur et de masse dans de ecoulements turbulents de Taylor-Couette avec flux axial

International audienceNous nous intéressons ici aux transferts de chaleur et de masse dans unsys eme de Taylor-Couette avec flux axial. Un dispositif permettant des mesures de vitesse et de coefficients de transferts á eté développé. Les régime etudiés sont turbulents : nombre de Reynolds axial entre 5600 et 11200 et entre 7900 et 79 millios pour le nombre de Taylor. Nous reportons le nombre de Nusselt en fonction du nombre de Reynolds axial et du nombre de Taylor ainsi que des mesures de vitesse. La présence de structures organisées proche du rotor á eté observée, ce qui est confirmé par un calcul DNS

Analysis of TerraSAR-X data sensitivity to bare soil moisture, roughness, composition and soil crust

Le comportement du signal radar TerraSAR-X en fonction des paramètres du sol (rugosité, humidité, structure) a été analysé sur des données 2009 et 2010. Les résultats montrent que la sensibilité du signal radar à l'humidité est plus importante pour des faibles incidences (25° en comparaison à 50°). Pour des fortes valeurs d'humidité, le signal TerraSAR-X est plus sensible à la rugosité du sol à forte incidence (50°). La forte résolution spatiale des données TerraSAR-X (1 m) permet de détecter la croûte de battance à l'échelle intra parcellaire. / Soils play a key role in shaping the environment and in risk assessment. We characterized the soils of bare agricultural plots using TerraSAR-X (9.5 GHz) data acquired in 2009 and 2010. We analyzed the behavior of the TerraSAR-X signal for two configurations, HH-25° and HH-50°, with regard to several soil conditions: moisture content, surface roughness, soil composition and soil-surface structure (slaking crust).The TerraSAR-X signal was more sensitive to soil moisture at a low (25°) incidence angle than at a high incidence angle (50°). For high soil moisture (N25%), the TerraSAR-X signal was more sensitive to soil roughness at a high incidence angle (50°) than at a low incidence angle (25°). The high spatial resolution of the TerraSAR-X data (1 m) enabled the soil composition and slaking crust to be analyzed at the within-plot scale based on the radar signal. The two loamy-soil categories that composed our training plots did not differ sufficiently in their percentages of sand and clay to be discriminated by the X-band radar signal.However, the spatial distribution of slaking crust could be detected when soil moisture variation is observed between soil crusted and soil without crust. Indeed, areas covered by slaking crust could have greater soil moisture and consequently a greater backscattering signal than soils without crust

The Impact of Protected Areas on Deforestation: An Exploration of the Economic and Political Channels for Madagascar’s Rainforests (2001-12)

Protected areas (PAs) remain the primary conservation instrument of Madagascar’s unique but threatened biodiversity. We combine matching and panel regressions in a quasi-natural experiment setting to analyze PAs’ environmental effectiveness annually between 2001 and 2012 and study two channels that moderate the impact: initial poverty rates and local variations in law enforcement. Our findings show that PAs have stabilized deforestation around a positive trend without having halted it. Their overall environmental impact is however limited: PAs created before the 2000 have helped to slow down deforestation by approximately 20%, meaning that 80% of forests are still cleared even though they are protected. As for new PA created from the mid-2000s, the early impact is statistically not significant. As a result, the total welfare impact of protection is currently uncertain. We show that PAs have been effective for municipalities where overall law enforcement was the lowest: PAs have helped to limit what we call opportunistic deforestation. Meanwhile, PAs have been poorly effective when poverty rates were high: when necessity is the driver of deforestation, PAs are not sufficient to slow down deforestation. As a consequence, effectively stopping deforestation in Madagascar will require ambitious policies to trigger the necessary agricultural transition for the country

A 3D model with shape prior information for biological structures reconstruction using Multiple-Angle Total Internal Reflection Fluorescence Microscopy

International audienceWe propose a new model for the reconstruction of biological struc- tures using Multiple-Angle Total Internal Reflection Fluorescence Microscopy (MA-TIRFM). This recent microscopy technique allows the visualization of sub-cellular structures around the plasma mem- brane which is of fundamental importance in the comprehension of exchanges mechanisms of the cell. We present a 3D reconstruction method based on a shape prior information on the observed struc- tures and robust to shot noise and background fluorescence. A nov- elty with respect to the state of the art is to propose a method allow- ing the recovery of multiple objects aligned along the axial axis. The optimization problem can be formulated as a minimization problem where both the number of objects in the model and their parame- ters have to be estimated. This difficult combinatorial optimization problem is tackled by using a Marked Point Process approach which allows modelling interactions between the objects in order to regu- larize the inverse problem. Finally, performances of the proposed method are evaluated on synthetic data and real data

Exploring New Physics in the C7-C7' plane

The Wilson coefficient C7 governing the radiative electromagnetic decays of B meson has been calculated to a very high accuracy in the Standard Model, but experimental bounds on either the magnitude or the sign of C7 are often model-dependent. In the present paper, we attempt at constraining both the magnitude and sign of C7 using a systematic approach. We consider already measured observables like the branching ratios of B \rightarrow Xs mu+ mu- and B \rightarrow Xs gamma, the isospin and CP asymmetries in B \rightarrow K* gamma, as well as AFB and FL in B \rightarrow K*l+l-. We also discuss the transverse observable AT2 which, once measured, may help to disentangle some of the scenarios considered. We explore the constraints on C7, C9, C10 as well as their chirality-flipped counterparts. Within our framework, we find that we need to extend the constraints up to 1.6 sigma to allow for the "flipped-sign solution" of C7. The SM solution for C7 exhibits a very mild tension if New Physics is allowed in dipole operators only. We provide semi-numerical expressions for all these observables as functions of the relevant Wilson coefficients at the low scale.Comment: 54 pages, 16 figures, 15 tables. Normalization factor introduced for the integrated AFB and FL in Sec.2.5 (Eq.2.35-2.38). Conclusions unchanged. Not updated in JHE