Predicting a User's Next Cell With Supervised Learning Based on Channel States

Knowing a user's next cell allows more efficient resource allocation and enables new location-aware services. To anticipate the cell a user will hand-over to, we introduce a new machine learning based prediction system. Therein, we formulate the prediction as a classification problem based on information that is readily available in cellular networks. Using only Channel State Information (CSI) and handover history, we perform classification by embedding Support Vector Machines (SVMs) into an efficient pre-processing structure. Simulation results from a Manhattan Grid scenario and from a realistic radio map of downtown Frankfurt show that our system provides timely prediction at high accuracy.Comment: The 14th IEEE International Workshop on Signal Processing Advances for Wireless Communications (SPAWC), Darmstadt : Germany (2013

Mean Field Energy Games in Wireless Networks

This work tackles the problem of energy-efficient distributed power control in wireless networks with a large number of transmitters. The problem is modeled by a dynamic game. Each transmitter-receiver communication is characterized by a state given by the available energy and/or the individual channel state and whose evolution is governed by certain dynamics. Since equilibrium analysis in such a (stochastic) game is generally difficult and even impossible, the problem is approximated by exploiting the large system assumption. Under an appropriate exchangeability assumption, the corresponding mean field game is well defined and studied in detail for special cases. The main contribution of this work is to show how mean field games can be applied to the problem under investigation and provide illustrative numerical results. Our results indicate that this approach can lead to significant gains in terms of energy-efficiency at the resulting equilibrium.Comment: IEEE Proc. of Asilomar Conf. on Signals, Systems, and Computers, Nov. 2012, Pacific Grove, CA, US

Stochastic Differential Games and Energy-Efficient Power Control

One of the contributions of this work is to formulate the problem of energy-efficient power control in multiple access channels (namely, channels which comprise several transmitters and one receiver) as a stochastic differential game. The players are the transmitters who adapt their power level to the quality of their time-varying link with the receiver, their battery level, and the strategy updates of the others. The proposed model not only allows one to take into account long-term strategic interactions but also long-term energy constraints. A simple sufficient condition for the existence of a Nash equilibrium in this game is provided and shown to be verified in a typical scenario. As the uniqueness and determination of equilibria are difficult issues in general, especially when the number of players goes large, we move to two special cases: the single player case which gives us some useful insights of practical interest and allows one to make connections with the case of large number of players. The latter case is treated with a mean-field game approach for which reasonable sufficient conditions for convergence and uniqueness are provided. Remarkably, this recent approach for large system analysis shows how scalability can be dealt with in large games and only relies on the individual state information assumption.Comment: The final publication is available at http://www.springerlink.com/openurl.asp?genre=article\&id=doi:10.1007/s13235-012-0068-

Cauchon diagrams for quantized enveloping algebras

Let $\mathfrak{g}$ be a finite dimensional complex simple Lie algebra, $\mathbb{K}$ a commutative field and $q$ a nonzero element of $\mathbb{K}$ which is not a root of unity. To each reduced decomposition of the longest element $w_0$ of the Weyl group $W$ corresponds a PBW basis of the quantised enveloping algebra $\mathcal{U}_q^+(\mathfrak{g})$, and one can apply the theory of deleting-derivation to this iterated Ore extension. In particular, for each decomposition of $w_0$, this theory constructs a bijection between the set of prime ideals in $\mathcal{U}_q^+(\mathfrak{g})$ that are invariant under a natural torus action and certain combinatorial objects called Cauchon diagrams. In this paper, we give an algorithmic description of these Cauchon diagrams when the chosen reduced decomposition of $w_0$ corresponds to a good ordering (in the sense of Lusztig \cite{Lu2}) of the set of positive roots. This algorithmic description is based on the constraints that are coming from Lusztig's admissible planes \cite{Lu2}: each admissible plane leads to a set of constraints that a diagram has to satisfy to be Cauchon. Moreover, we explicitely describe the set of Cauchon diagrams for explicit reduced decomposition of $w_0$ in each possible type. In any case, we check that the number of Cauchon diagrams is always equal to the cardinal of $W$. In \cite{CM}, we use these results to prove that Cauchon diagrams correspond canonically to the positive subexpressions of $w_0$. So the results of this paper also give an algorithmic description of the positive subexpressions of any reduced decomposition of $w_0$ corresponding to a good ordering.Comment: The section 4 was rewritten and split into section 4 and 5 for more clarity. An english version is now availabl

Spatio-temporal wavelet regularization for parallel MRI reconstruction: application to functional MRI

Parallel MRI is a fast imaging technique that enables the acquisition of highly resolved images in space or/and in time. The performance of parallel imaging strongly depends on the reconstruction algorithm, which can proceed either in the original k-space (GRAPPA, SMASH) or in the image domain (SENSE-like methods). To improve the performance of the widely used SENSE algorithm, 2D- or slice-specific regularization in the wavelet domain has been deeply investigated. In this paper, we extend this approach using 3D-wavelet representations in order to handle all slices together and address reconstruction artifacts which propagate across adjacent slices. The gain induced by such extension (3D-Unconstrained Wavelet Regularized -SENSE: 3D-UWR-SENSE) is validated on anatomical image reconstruction where no temporal acquisition is considered. Another important extension accounts for temporal correlations that exist between successive scans in functional MRI (fMRI). In addition to the case of 2D+t acquisition schemes addressed by some other methods like kt-FOCUSS, our approach allows us to deal with 3D+t acquisition schemes which are widely used in neuroimaging. The resulting 3D-UWR-SENSE and 4D-UWR-SENSE reconstruction schemes are fully unsupervised in the sense that all regularization parameters are estimated in the maximum likelihood sense on a reference scan. The gain induced by such extensions is illustrated on both anatomical and functional image reconstruction, and also measured in terms of statistical sensitivity for the 4D-UWR-SENSE approach during a fast event-related fMRI protocol. Our 4D-UWR-SENSE algorithm outperforms the SENSE reconstruction at the subject and group levels (15 subjects) for different contrasts of interest (eg, motor or computation tasks) and using different parallel acceleration factors (R=2 and R=4) on 2x2x3mm3 EPI images.Comment: arXiv admin note: substantial text overlap with arXiv:1103.353

Variable density sampling based on physically plausible gradient waveform. Application to 3D MRI angiography

Performing k-space variable density sampling is a popular way of reducing scanning time in Magnetic Resonance Imaging (MRI). Unfortunately, given a sampling trajectory, it is not clear how to traverse it using gradient waveforms. In this paper, we actually show that existing methods [1, 2] can yield large traversal time if the trajectory contains high curvature areas. Therefore, we consider here a new method for gradient waveform design which is based on the projection of unrealistic initial trajectory onto the set of hardware constraints. Next, we show on realistic simulations that this algorithm allows implementing variable density trajectories resulting from the piecewise linear solution of the Travelling Salesman Problem in a reasonable time. Finally, we demonstrate the application of this approach to 2D MRI reconstruction and 3D angiography in the mouse brain.Comment: IEEE International Symposium on Biomedical Imaging (ISBI), Apr 2015, New-York, United State

Status and Contracts in Industrial Relations: "La Refondation sociale", a new Bottle for an old (French) Wine?

"Seit 1999 betreibt der französische Arbeitgeberverband (Medef) eine radikale Umwandlung des institutionellen Rahmens der industriellen Beziehungen und des Wohlfahrtsstaats. Diese Initiative wird als soziale Neugründung bezeichnet. Um die Bedeutung dieses Vorgangs würdigen zu können, wird in dem Papier zunächst ein kurzer historischer Überblick über die Institutionen der industriellen Beziehungen in Frankreich gegeben. Besondere Aufmerksamkeit wird dabei den schändlichen korporatistischen Mechanismen geschenkt, die Arbeit und Kapital die Aufgabe übertragen, staatliche Normen in diesem Bereich anzuwenden, zu konkretisieren oder in definierten Fällen auch zu modifizieren. Die Autoren hinterfragen anschließend die Annahmen und Motive hinter dem Anspruch der sozialen Neugründer, die kollektive Autonomie der Sozialpartner gegenüber staatlichen Gesetzen zu stärken, indem sie zeigen, dass die dichotomische Konzeption von Gesetz und Vertrag nicht mit der komplexen institutionellen Wirklichkeit übereinstimmt. Abschließend wird die Annahme begründet, dass das wichtigste von Medef angestrebte Ziel in der Förderung der Vertragsfreiheit auf der untersten, der betrieblichen Ebene der industriellen Beziehungen besteht, um die dezentralen Gestaltungsmöglichkeiten der Unternehmen zu erweitern. Dies würde allerdings eine Rückkehr zum individualistischen Begriff des Einzelvertrags im bürgerlichen Recht als Basis der industriellen Beziehungen implizieren, also zum Gegenteil dessen, worauf Arbeitsrecht und industrielle Beziehungen seit dem späten 19. Jahrhundert aufgebaut wurden." (Autorenreferat)"Since 1999, the main French employers organisation (Medef) has been promoting a radical transformation of the institutional framework of industrial relations and the welfare state. This initiative, known as the Social Re-foundation agenda, has started to be implemented through a new cycle of inter-sectoral negotiations with the unions, on major issues such as the reform of the social security and unemployment insurance schemes: the ways and means for the development of collective bargaining , etc. Echoing the trends observed in many national industrial relations systems in Europe and also at the UE level, the Social Re-foundation represents the most ambitious attempt ever made in France at redefining the boundaries between legal and contractual rules in the regulation of employment relations. In order to assess the issues at stake with the Social Re-foundation , the paper first provides a brief historical overview of the French industrial relations institutions, focusing on the shameful corporatist mechanisms through which labour and capital were authorised to apply, spell out, in some cases also modify state regulations in this field. Then the authors question the assumptions and the motives of the social re-founders when they claim to promote the collective autonomy of social partners against state law, by showing how their dualistic conception of law and contract is not in accordance with the complex institutional reality. Finally, it is suggested that the main aim of the Medef s strategy is to favour contractual autonomy at the lowest levels of collective bargaining, so as to develop firms self-regulation. This would also mean a return to the individualist contractual philosophy of civil law, i.e the very opposite conception on which labour law and industrial relations institutions have been built up since the late 19th century." (author's abstract

Méthodes de volumes finis en maillages variables pour des équations hyperboliques en une dimension

Le but de ce travail est de présenter des méthodes numériques utilisant des volumes finis sur des maillages variables (mobiles et potentiellement auto-adaptatifs) pour la résolution d'équations hyperboliques linéaires ou non-linéaires en une dimension d'espace. La difficulté pour les maillages raffinés provient du fait que nous devons utiliser un schéma implicite en temps pour des raisons de stabilité. Nous regardons ici un schéma implicite localement. Parallèlement, nous modifions les schémas envisagés afin de les écrire en maillages mobiles à topologie non constante

: Rapport final

Rapport de recherche réalisé en réponse à l’appel d’offres du Commissariat général du Plan « L’évolution des relations professionnelles en France ».L'objet de cette recherche est d'examiner comment les composantes du système français de relations professionnelles — ses acteurs, ses règles et ses institutions — tendent à se reconfigurer pour faire face aux nouveaux enjeux résultant des risques du travail et de l'emploi, en subissant l'influence des formes d'organisation et d'action des pouvoirs publics et privés (entreprises et regroupements d'employeurs). Sept « chantiers », eux-mêmes souvent constitués de plusieurs études de cas, ont été retenus ; le principe général ayant présidé à la sélection des terrains d'investigation est celui de la confrontation entre une variété d'espaces de régulation (nationaux et teritoriaux) dans lesquels sont mises en tension les formes traditionnelles d'appréhension et de prise en charge, par les partenaires sociaux et les pouvoirs publics, des risques du travail et de l'emploi. La référence à la problématique des risques n'est pas artificielle, dès lors que l'on ne reste pas prisonnier de logiques nominalistes. Elle a en effet un double avantage : elle permet d'apprécier le degré de formalisation des problèmes en jeu ; elle invite à s'interroger sur les connaissances mobilisées pour construire les problèmes en cause avant éventuellement, de les convertir en risques, en tout cas en enjeux politiques. Ce processus de problématisation et de mise sur agenda s'opère au sein de réseaux d'acteurs hétérogènes, mêlant, dans des proportions variables selon les cas, autorités politico-administratives et représentants des intérêts socioéconomiques. Les types de règles produites peuvent emprunter aux formalismes « classiques » des relations professionnelles (accords collectifs) ou à des formules « contractuelles » relevant davantage de la « soft law » (chartes de bonne conduite) ou des instruments de l'action publique « négociée » (du type « contrats d'objectifs »). L'usage de la notion de régime d'action collective permet précisément d'englober ces différentes configurations d'acteurs et de règles. On distingue ainsi plusieurs régimes d'action collective explicités dans le corps du texte selon que celle-ci se fait « tutélaire », « régulatoire », « facilitatrice », « entrepreneuriale », « opportuniste ». Bien évidemment, ces novations bousculent le jeu classique de la négociation collective, appellent une mobilisation accrue de l'expertise et de la réflexivité des parties prenantes, au risque d'un excès de procéduralisation conjuguant coûts de transaction et coûts de traduction et conjurant les risques de prises de responsabilité politique. Sous le surplomb du principe de précaution, se fait jour une tendance à réunifier les approches sectorielles du social, en particulier en matière de travail et d'emploi : l'impact sur la santé des personnes des conditions d'emploi et de travail – que ce soit au regard de la précarité des parcours ou de la gestion des ressources humaines dans la firme — re-légitime économiquement et politiquement une gestion décloisonnée des divers secteurs de l'action publique. Autrement dit, le développement durable des ressources humaines tend à s'imposer progressivement aux décideurs publics et privés, à tout le moins, comme un thème légitime de débat et demain, peut-être, un objet de décision «précautionneuse »