A New Adaptive Filter Approach for Acoustic Echo Canceller in Teleconference Systems

A flexible Frequency domain Block Recursive Least Squares (FBRLS) algorithm using the Multi-Delay Filter (MDF) is presented throughout this paper. In term of performances, the MDF-FBRLS adaptive filter introduces smaller block delay and is usually faster and suitable for ideal time-varying system such as an acoustic echo in a teleconference room. The implementation of the FBRLS algorithm using MDF adaptive filter allows reducing the FFT size and consequently optimizing the hardware implementation that could be performed using standard DSP chips. These good performances are achieved by using smaller block size and updating frequently the weight vectors which will reduce the total execution time of the adaptive process. Simulation results show that the MDF-FBRLS algorithm is better than the FBRLS algorithm in terms of the total execution time and the efficiency of the computational complexity

Simple pre-distortion schemes for improving the power efficiency of SOA-based IR-UWB over fiber systems

International audienceIn this paper, we investigate the usage of SOA for reach extension of an impulse radio over fiber system. Operating in the saturated regime translates into strong nonlinearities and spectral distortions, which drops the power efficiency of the propagated pulses. After studying the SOA response versus operating conditions, we have enhanced the system performance by applying simple analog pre-distortion schemes for various derivatives of the Gaussian pulse and their combination. A novel pulse shape has also been designed by linearly combining three basic Gaussian pulses, offering a very good spectral efficiency (>55%) for a high power (0 dBm) at the amplifier input. Furthermore, the potential of our technique has been examined considering a 1.5 Gbps-OOK and 0.75 Gbps-PPM modulation schemes. Pre-distortion proved an advantage for a large extension of optical link (150 Km), with an inline amplification via SOA at 40 Km

Improving the power efficiency of SOA-based UWB over fiber systems via pulse shape randomization

International audienceA simple pulse shape randomization scheme is considered in this paper for improving the performance of Ultra Wide band (UWB) communication systems using On Off Keying (OOK) or Pulse Position Modulation (PPM) formats. The advantage of the proposed scheme, which can be either employed for Impulse Radio (IR) or for carrier-based systems, is first theoretically studied based on closed-form derivations of power spectral densities. Then, we investigate an application to an IR-UWB over optical fiber system, by utilizing the 4-th and 5-th orders of Gaussian derivatives. Our approach proves to be effective for 1 Gbps-PPM and 2 Gbps-OOK transmissions, with an advantage in terms of power efficiency for short distances. We also examine the performance for a system employing an in-line Semiconductor Optical Amplifier (SOA) with the view to achieve a reach extension, while limiting the cost and system complexity

STEM nanoanalysis of Au/Pt/Ti-Si3N4 interfacial defects and reactions during local stress of SiGe HBTs

A new insight on the behavior of metal contact-insulating interfaces in SiGe heterojunction bipolar transistor is given by high-performance aberration-corrected scanning transmission electron microscopy (STEM) analysis tools equipped with sub-nanometric probe size. It is demonstrated that the presence of initial defects introduced during technological processes play a major role in the acceleration of degradation mechanisms of the structure during stress. A combination of energy-filtered transmission electron microscopy analysis with high angle annular dark field STEM and energy dispersive spectroscopy provides strong evidence that migration of Au-Pt from the metal contacts to Ti/Si3N4 interface is one of the precursors to species interdiffusion and reactions. High current densities and related local heating effects induce the evolution of the pure Ti initial layer into mixture layer composed of Ti, O, and N. Local contamination of Ti layers by fluorine atoms is also pointed out, as well as rupture of TiN thin barrier layer

Media's portrayal of social services' work and profession : A qualitative study on social workers' experience of the impact of media reporting on child and youth investigations

Based on media's influence on society, the study aims to investigate how social workers feel regarding their work with children and youth investigations which is affected by how the media portrays social services and social work. The study also aims to investigate how the media affects social workers as a profession. Through its reporting and review of social services, the media can reach out, generate interest, and create opinions among the public. Social workers who work with child and youth investigations establish strong emotions through their professional role and through their decisions. Previous research shows that social workers nationally and internationally share the image that the media's portrayal of social services and their work in negative terms is affected by social work and professions to varying extents. In this study, we have chosen to use scientific reviewed articles from Australia, England, New Zealand, USA, and Sweden. The implementation of the study consisted of five semi-structured interviews with social workers working in Malmo, which together with our theories; The agenda setting theory, the organization theory, and the profession theory, form the basis for our analysis and results. The result of the study shows that the social workers we interviewed experience a common image that the media's reporting regarding the social service and its work with child and youth investigations is predominantly negative. Although they see media's negative reporting as a good thing due it leads to improvement and keeps the work legally secure. Furthermore, our interviewed participants share a common view that a good collaboration with the media could have led to a positive image of the social services but also the profession. Utifrån medias inflytande över samhället syftar studien till att undersöka hur socialsekreterare upplever att deras arbete med barn- och ungdomsutredningar påverkas av hur media framställer socialtjänsten och det sociala arbetet men även hur media påverkar socialsekreterare som profession. Media kan genom sin rapportering och granskning av socialtjänsten nå ut, väcka, intresse och bilda åsikter hos allmänheten. Socialsekreterare som arbetar med barn- och ungdomsutredningar väcker i sin tur starka känslor genom sin yrkesroll och sina beslut. Tidigare forskning visar att socialsekreterare nationellt och internationellt delar bilden av att medias framställning av socialtjänsten och dess arbete i negativ bemärkelse påverkar det sociala arbetet och professionen i olika utsträckningar. Vi har i denna studie valt att använda oss utav vetenskapligt granskade artiklar från Australien, England, Nya Zeeland, USA och Sverige. Studiens genomförande bestod av fem semistrukturerade intervjuer med socialsekreterare yrkesverksamma i Malmö, vilket tillsammans med våra teorier; dagordningsteorin, organisationsteorin och professionsteorin utgör grunden för vår analys och vårt resultat. Resultatet i studien visar att socialsekreterare som vi intervjuat upplever en gemensam bild av att medias rapportering gällande socialtjänsten och dess arbete med barn-och ungdomsutredningar övervägande negativ men menade på att den negativa rapporteringen leder till att socialtjänstens arbete granskas vilket är en fördel så att arbetet förblir rättssäkert. Vidare delar våra intervjudeltagare bilden av att ett bra samarbete med media hade kunnat leda till en positiv bild av socialtjänsten men även professionen.  

Le Transistor Bipolaire à Hétérojonction Si/SiGe sous contraintes électromagnétiques : des dégradations électriques à l'analyse structurale

Cette thèse propose une nouvelle méthodologie pour l étude de la fiabilité des Transistors Bipolaires à Hétérojonctions (TBHs) en technologie SiGe. L originalité de cette étude vient de l utilisation d une contrainte électromagnétique efficace et ciblée à l aide du banc champ proche. Ce type de contrainte a permis de dégrader les performances de ce composant en mettant en évidence certains mécanismes de défaillance. Les caractérisations statiques ont montré la présence des courants de fuite à l interface Si/SiO2, non seulement entre la base et l émetteur, mais aussi entre la base et le collecteur. Ceci est attribué à un phénomène de piégeage induit par des porteurs chauds qui ont été engendrés pendant la durée du vieillissement. Ce phénomène a été abordé par la modélisation physique en étudiant l influence des pièges d interfaces sur la dérive des performances électriques du TBH. Afin de visualiser les défaillances qui peuvent être détectées par microscopie, des observations en haute résolution MET (Microscope Electronique à Transmission) et des analyses EDS (Energy Dispersive Spectroscopy) ont été présentées. Ces analyses microscopiques ont mis en évidence les dégradations des couches de titane autour de l émetteur, de la base et du collecteur. Ces dégradations sont attribuées à un phénomène de migration de l or (Au) vers le titane (Ti) due à la forte densité de courant induite par vieillissement. Ces réactions Au-Ti provoquent une augmentation de la résistivité des couches conductrices et expliquent une partie de la dégradation significative des performances dynamiques du TBH.This work proposes a new methodology for studying the reliability of the Heterojunction Bipolar Transistors (HBTs) in SiGe technology. The originality of this study comes from the use of a targeted electromagnetic field stress by using the near field bench. This type of stress has to degrade the performance of this component causing failure mechanisms. The DC characterizations showed the presence of leakage currents at Si/SiO2 interface, not only between the base and the emitter, but also between the base and the collector. This is attributed to a trapping phenomenon induced by hot carriers which have been generated during stress. This phenomenon has been addressed by the physical modeling, by studying the influence of interface traps on the drift of the HBT characteristics. To identify the failures that can be detected by microscopy, characterization of the structure before and after ageing was performed by Transmission Electron Microscopy (TEM) and energy dispersive spectroscopy (EDS). These analyses revealed the degradation of the titanium layers around the emitter, the base and the collector. The degradations are attributed to the gold (Au) migration into the titanium (Ti) due to the high current density induced by stress. Some of these Au Ti reactions are known to increase the resistivity of the conducting layers which directly affects the HBTs dynamic performances.ROUEN-BU Sciences Madrillet (765752101) / SudocSudocFranceF

Fast Convolution Using Generalized Sliding Fermat Number Transform with Application to Digital Filtering

International audienceThis paper is about a new efficient method for the implementation of a Block Proportionate Normalized Least Mean Square (BPNLMS++) adaptive filter using the Fermat Number Transform (FNT). An efficient state space method for implementing the FNT over rectangular windows is used in the cases where there is a large overlap between the consecutive input signals. This is called Generalised Sliding Fermat Number Transform (GSFNT) and is useful for reducing the computational complexity of finite ring convolvers and correlators. In this contribution, we propose, as a first objective, an efficient state algorithm with the purpose of reducing the complexity of inverse FNT. This algorithm, called Inverse Generalised Sliding Fermat Number Transform (IGSFNT) uses the technique of Generalised Sliding, associated to matricial calculations in the Galois Field. The second objective is to realize an implementation of the BPNLMS++ adaptive filter using GSFNT and IGSFNT, which can significantly reduce the computation complexity of the filter implantation on digital processors

OFDM signal up and down frequency conversions by a sampling method using a SOA-MZI

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Up and down frequency conversion of a QPSK signal by an all-optical radiofrequency sampling mixer based on a semiconductor optical amplifier Mach-Zehnder interferometer

International audienceAn all-optical sampling mixer based on a Semiconductor Optical Amplifier Mach-Zehnder Interferometer is performed. The frequency properties of a sampled signal are exploited to obtain both up and down frequency conversion of QPSK data. The optical pulse source, generating 10-ps width pulses at the repetition rate of 7.8 GHz as a sampling signal, allows operation in the 0.5-39.5 GHz range. The conversion gain of the all-optical sampling mixer is measured over all the frequency range. It varies over this range from 20.4 to 0 dB for frequency down-conversion and from 15.5 to -13.4 dB for frequency up-conversion. QPSK data at symbol rates between 8 MSymb/s to 128 MSymb/s are frequency converted. The Error Vector Magnitude is used to evaluate the quality of the frequency conversion. Exploitable EVMs in the range 14 to 27.4% are reached for up-conversion operation to the higher frequency for all the symbol rates. For down-conversion the EVM varies from 6.7 to 29.2% at the symbol rate of 64 MSymb/s for all the frequency range

Transposition de fréquence de signaux radiofréquences par échantillonnage tout-optique

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