Is training of adaptive equalizers still useful ?

International audienceWe present a novel unsupervised adaptive equalizer. It has the same computational complexity, convergence speed and steady-state MSE as a trained LMS adaptive DFE, but it is not subject to error propagation. Therefore, it can equalize even severe and/or quickly varying channels. This follows from the very structure of the equalizer, which allows a completely reversible transition between (i) a linear structure in the starting mode : the decoupled cascade of a recursive adaptative predictor and a transversal phase equalizer and (ii) a classical DFE in the tracking mode. The equalizer behaviour is fully satisfactory during hours of real underwater communications. It reaches the standard of trained equalizers. Hence the question in the title

Egalisation autodidacte adaptative : Application aux systèmes d'accès multiples à répartition dans le temps

L'égalisation adaptative, autodidacte ou entraînée, nécessite en général un temps de convergence qui s'accomode mal des systèmes d'accès multiples à répartition dans le temps (AMRT), systèmes dans lesquels la transmission s'effectue en mode paquets. Par ailleurs le nombre d'applications utilisant ce type d'accès ne cesse de croître. De ce point de vue, il paraît opportun de réfléchir à des solutions permettant à un égaliseur de converger sur des paquets (ou blocs) courts, comportant quelques dizaines de symboles. Parmi les applications visées on peut citer, de manière non exhaustive, le GSM, le DECT, etc. Dans chacun de ces systèmes, le bloc comporte une séquence connue dont la longueur s'avère généralement insuffisante pour permettre la convergence d'un égaliseur adaptatif entraîné. Au travers de cet article nous allons montrer que l'égaliseur autodidacte adaptatif récemment introduit par Labat et al peut s'accomoder de cette contrainte, avec une complexité raisonnable

Environmental characterisation of retification process by-products (liquid and gaseous wastes)

6th International Symposium “Environment and Wood Preservation” Cannes-Mandelieu, France 7-8 February 2005 14 pagesIn order to reduce environmental risks during the service life of the treated wood and to find new alternative developments on the durability of wood, some research and technology development have been made on thermal treatment. The retification process is one of these processes. The retification process induces chemical modification of the lignin and cellulosic components and modifies the intrinsic properties of wood : efficient increases the durability against fungi and insects, increases of the dimensional stability, decrease of the mechanical properties. The interest of this process is to reduce the environmental impact during the service life. In order to confirm the high interest of this process for the reduction of the environmental impact, an environmental characterisation of wastes on pilot plant have been carried out. Chemical analysis on gaseous and liquid effluents have been performed. An energetic assessment has been realised. The results indicate the high interest of this process in terms of possible biodegradable wastes and chemical valorisation interest, interest on energetic consumption in comparison with other wood processing treatment, interest on using retification treated wood in flooring according to indoor air quality requirements

Characterization Study of CO2, CH4, and CO2/CH4 Hydroquinone Clathrates Formed by Gas–Solid Reaction

Hydroquinone (HQ) is known to form organic clathrates with some gaseous species such as CO2 and CH4. This work presents spectroscopic data, surface and internal morphologies, gas storage capacities, guest release temperatures, and structural transition temperatures for HQ clathrates obtained from pure CO2, pure CH4, and an equimolar CO2/CH4 mixture. All analyses are performed on clathrates formed by direct gas–solid reaction after 1 month’s reaction at ambient temperature conditions and under a pressure of 3.0 MPa. A collection of spectroscopic data (Raman, FT-IR, and 13C NMR) is presented, and the results confirm total conversion of the native HQ (α-HQ) into HQ clathrates (β-HQ) at the end of the reaction. Optical microscopy and SEM analyses reveal morphology changes after the enclathration reaction, such as the presence of surface asperities. Gas porosimetry measurements show that HQ clathrates and native HQ are neither micro- nor mesoporous materials. However, as highlighted by TEM analyses and X-ray tomography, α- and β-HQ contain unsuspected macroscopic voids and channels, which create a macroporosity inside the crystals that decreases due to the enclathration reaction. TGA and in situ Raman spectroscopy give the guest release temperatures as well as the structural transition temperatures from β-HQ to α-HQ. The gas storage capacity of the clathrates is also quantified by means of different types of gravimetric analyses (mass balance and TGA). After having been formed under pressure, the characterized clathrates exhibit exceptional metastability: the gases remain in the clathrate structure at ambient conditions over time scales of more than 1 month. Consequently, HQ gas clathrates display very interesting properties for gas storage and sequestration applications

Breast cancer stem cells: tools and models to rely on

There is increasing evidence for the "cancer stem cell (CSC) hypothesis", which holds that cancers are driven by a cellular component that has stem cell properties, including self-renewal, tumorigenicity and multi-lineage differentiation capacity. Researchers and oncologists see in this model an explanation as to why cancer may be so difficult to cure, as well as a promising ground for novel therapeutic strategies. Given the specific stem cell features of self-renewal and differentiation, which drive tumorigenesis and contribute to cellular heterogeneity, each marker and assay designed to isolate and characterize CSCs has to be functionally validated. In this review, we survey tools and markers available or promising to identify breast CSCs. We review the main models used to study breast CSCs and how they challenge the CSC hypothesis

Improved Blind Decision Equalizer with self-adapted structure for High Order QAM signals

International audienceThis paper brings some noticeable improvements to a blind decision feedback equalizer recently introduced and mainly characterized by its self-adapted structure. In its starting-up mode, this equalizer is linear and recursive and controlled by a withening criterion for the recursive part and the Godard criterion for the transversal one. However, in the case of high order QAM signals, the whole performances can be largely improved when the Godard algorithm is gradually replaced by the radius directed algorithm. This novel switching procedure is investigated for a 64-QAM on a typical telephone line and on a severe non minimum phase channel. The results are really convincing since this strategy brings a more accurate equalization, which allows the new equalizer to safely reach its final state of decision feedback equalize (tracking mode). Needless to say that such an improved blind equalizer turns out to be particulary well-suited for applications such as HDT

Blind spatio-temporal Decision Feedback Equalization : a Self Adaptative Structure Approach

International audienceIt is well known that the performances of any receiver can be improved by means of equalization and diversity combining. However, the problem of the blind adaptation is entirely open in the case of decision feedback equalization. This paper attempts to introduce a new scheme of blind spatio-temporal equalizer whose main feature is its ability to self-adapt both its structure and its criteria to the encountered situations. Simulations results are given for a 4-QAM signal and compared to those of the classical constant modulus algorithm (CMA) spatio-temporal equalizer. The results are really convincing : it clearly appears that the new equalizer exhibits very good performances in terms of mean square erro, bit error rate as well as convergence speed. From all these points of view, it largely outperforms the classical CMA linear equalizer. As a result, this new blind spatio-temporal equalizer turns out to be very attractive for many applicationsIt is well known that the performances of any receiver can be improved by means of equalization and diversity combining. However, the problem of the blind adaptation is entirely open in the case of decision feedback equalization. This paper attempts to introduce a new scheme of blind spatio-temporal equalizer whose main feature is its ability to self-adapt both its structure and its criteria to the encountered situations. Simulations results are given for a 4-QAM signal and compared to those of the classical constant modulus algorithm (CMA) spatio-temporal equalizer. The results are really convincing : it clearly appears that the new equalizer exhibits very good performances in terms of mean square erro, bit error rate as well as convergence speed. From all these points of view, it largely outperforms the classical CMA linear equalizer. As a result, this new blind spatio-temporal equalizer turns out to be very attractive for many applications

Blind adaptive multiple-input decision-feedback equalizer with a self-optimized configuration

International audienceThis paper introduces a novel blind adaptive multiple-input decision-feedback equalizer (MI-DFE) which is basically characterizd by its ability to self-optimize its configuration, in terms of both structure and criteria, according to the severity of the transmission medium. In the first running mode, the novel equalizer is recursive, linear and "blindly" adapted by criteria leading to a solution closely related to the minimum MSE solution. In the second running mode, it becomes the conventional MI-DFE. From the viewpoints of both robustness and spectral efficiency, this equalizer proves to be very attractive since it avoids pathological behaviors, often encountered with the conventional trained MI-DFE, while requiring no training sequence. Furthermore, its very high speed of convergence renders it competitive in various standard applications, even in the case of burst mode transmission systems. Finally the novel blingd MI-DFE has been successfully tested on underwater acoustic communications signals, in a very severe context. The results are clearly convincing

Egalisation Autodidacte Adaptative : Application aux Systèmes d'Accès à Répartition dans le temps

International audienceAdaptive blind or trained equalization usually involves a convergence time that is not compatible with time division multiple access (TDMA) systems. Furthermore, the number of applications using this king of access is still increasing, form this point of view, it seems of prime importance to lead a global reflection about solutions allowing an adaptive equalizer to converge very quickly, that is, on a few tens of symbol periods and even less. Among the current applications, one can cite, in a non exhaustive way, the GSM and DECT standards. In each system, the bursts contain a training sequence, the lengh of which is generally insufficient to allow the convergence of an adaptive equalizer, even in a trained mode. In this contribution, we show that the novel and very powerful adaptive blind equalizer recently proposed by Labat et al can take up this challenge at the prince of a reasonable complexity.L'égalisation adaptative, autodidacte ou entraînée, nécessite en général un temps de convergence qui s'accomode mal des systèmes d'accès multiples à répartition dans le temps (AMRT), systèmes dans lesquels la transmission s'effectue en mode paquets. Par ailleurs le nombre d'applications utlisant ce type d'accès ne cesse de croître. De ce point de vue, il paraît opportun de réfléchir à des solutions permettant à un égaliseur de converger sur des paquets (ou blocs) courts, comportant quelques dizaines de symboles. Parmi les applications visées on peut citer, de manière non exhaustive, le GSM, le DECT, etc. Dans chacun de ces systèmes, le bloc comporte une séquence connue dont la longueur s'avère généralement insuffisante pour permettre la convergence d'un égaliseur adaptatif entraîné. Au travers de cet article, nous allons montrer que l'égaliseur autodidacte adaptatif récemment introduit par Labat et al peut s'accomoder de cette contrainte, avec une complexité raisonnable