A Parametric Replay-Based Framework for Underwater Acoustic Communication Channel Simulation

International audienceThis paper lays the foundation of an underwater acoustic channel simulation methodology that is halfway between parametric modeling and stochastic replay of at-sea measurements of channel impulse responses. The motivation behind this approach is to extend the scope of use of replay-based methods by allowing some parameterization of the channel properties while complying with some level of realism. Based on a relative entropy minimization between the original channel impulse response and the simulated one, the idea is to deliberately distort the original channel statistics in order to meet some specified constraints

Achievable Rates of Underwater Acoustic OFDM Systems over Highly Dispersive Channels

International audienceUnlike the capacity of other channels, the capacity of the shallow water UAC channel has been seldomly addressed. Motivated by recent results in information theory, this paper investigates achievable rates of underwater acoustic OFDM systems. We consider channels where time and frequency dispersion is high enough that (i) neither the transmitter nor the receiver can have a priori knowledge of the channel state information, and (ii) intersymbol/intercarrier interference (ISI/ICI) cannot be neglected in the information theoretic treatment

Intercomparison of Permittivity Measurement Techniques for Ferroelectric Thin Layers

International audienceThe dielectric properties of a KTa0.65Nb0.35O3 (KTN) ferroelectric composition for a submicronic thin layer were measured in the microwave domain using different electromagnetic characterization methods. Complementary experimental techniques (broadband methods versus resonant techniques, waveguide versus transmission line) and complementary data processing procedures (quasi-static theoretical approaches versus full-wave analysis) were selected to investigate the best way to characterize ferroelectric thin films. The measured data obtained from the cylindrical resonant cavity method, the experimental method that showed the least sources of uncertainty, were taken as reference values for comparisons with results obtained using broadband techniques. The error analysis on the methods used is discussed with regard to the respective domains of validity for each method; this enabled us to identify the best experimental approach for obtaining an accurate determination of the microwave dielectric properties of ferroelectric thin layers

Overlap and Mutual Distinctions between Clinical Recovery and Personal Recovery in People with Schizophrenia in a One-Year Study

Recovery is a multidimensional construct that can be defined either from a clinical perspective or from a consumer-focused one, as a self-broadening process aimed at living a meaningful life beyond mental illness. We aimed to longitudinally examine the overlap and mutual distinctions between clinical and personal recovery. Of 1239 people with schizophrenia consecutively recruited from the FondaMental Advanced Centers of Expertise for SZ network, the 507 present at one-year did not differ from those lost to follow-up. Clinical recovery was defined as the combination of clinical remission and functional remission. Personal recovery was defined as being in the rebuilding or in the growth stage of the Stages of Recovery Instrument (STORI). Full recovery was defined as the combination of clinical recovery and personal recovery. First, we examined the factors at baseline associated with each aspect of recovery. Then, we conducted multivariable models on the correlates of stable clinical recovery, stable personal recovery, and stable full recovery after one year. At baseline, clinical recovery and personal recovery were characterized by distinct patterns of outcome (i.e. better objective outcomes but no difference in subjective outcomes for clinical recovery, the opposite pattern for personal recovery, and better overall outcomes for full recovery). We found that clinical recovery and personal recovery predicted each other over time (baseline personal recovery for stable clinical recovery at one year; P =. 026, OR = 4.94 [1.30-23.0]; baseline clinical recovery for stable personal recovery at one year; P =. 016, OR = 3.64 [1.31-11.2]). In short, given the interaction but also the degree of difference between clinical recovery and personal recovery, psychosocial treatment should target, beyond clinical recovery, subjective aspects such as personal recovery and depression to reach full recovery. © 2021 The Author(s). Published by Oxford University Press on behalf of the Maryland Psychiatric Research Center. All rights reserved.Sorbonne Universités à Paris pour l'Enseignement et la RechercheFondaMental-Cohorte

Estimation par régions de confiance en trajectographie passive

En calculant de véritables régions de confiance, on montre qu'en Trajectographie Passive à partir d'Azimuts (TPA) les ellipses d'incertitude habituelles dans le plan (X,Y) donnent souvent des indications erronnées sur la précision effective. On propose ensuite une approximation en 1/R des regions de confiance en TPA, moins coûteuse à obtenir que les véritables regions, mais plus précise que les ellipses habituelles

Détection et localisation de sources faibles par intégration long terme

- On présente une méthode d'intégration dynamique (ou de voies défilantes) long terme, applicable de manière panoramique en gisement et fréquence. Cette méthode permet d'améliorer les performances théoriques en détection BE sur des sources proches et silencieuses dont le gisement défile

Manoeuvre optimale en trajectographie passive a partir d'azimut

En Trajectographie Passive par Azimut (TPA), la trajectoire de l'observateur influe fortement sur la précision d'estimation de la trajectoire de l'émetteur. Nous appliquons ici des éléments de la théorie du contrôle optimal pour déterminer la trajectoire de l'observateur qui optimise un critère de précision basé sur la matrice d'information de Fisher. Les conditions nécessaires d'optimalité sont établies et intégrées numériquement. Finalement, des exemples de trajectoires optimales sont présentés

Shallow water acoustic communications : how far are we from the channel capacity ?

International audienceThis paper focuses on the capacity of the underwater acoustic communications (UAC) channel under realistic assumptions: time-varying multi-paths channel, modelled as a stochastic doubly-spread frequency-selective channel,unknown actual realization of the channel at both transmitter and receiver, constraints on both transmitted power (rms and/or peak) and available frequency bandwidth. The exact channel capacity under such assumptions is still unknown. Therefore, several bounds for this capacity are given and then numerically assessed for a fewtypical shallow water UAC channels. The main conclusion is that, even with the above comprehensive set of demanding assumptions, as far as the theoretical channel capacity is considered, transmission with higher than often now spectral efficiency (e.g. 2 to 4 bits/sec/Hz) appears as a reasonable objective in typical time-varying underwater acoustic communication channels, providing SNR about 15 to 20 dB

High fidelity simulation tools for performance assessment of underwater acoustic communications modems

International audienceNew attractive techniques, such as multi-carrier modulations, efficient channel coding, iterative reception algorithms, and use of multiple antennas at reception or transmission, are now emerging in underwater acoustic communications (UAC). According to the published results, these techniques could provide, within the next years, a significant breakthrough with respects to the critical issue of robust and high bitrate (a few kbits/sec) tactical communications with submarines and/or AUV). Thales Underwater Systems (TUS), as a UAC equipments manufacturer and integrator, is therefore very interested in performance assessment of these techniques, either by implementing the corresponding signaling schemes and algorithms, or by testing them as black boxes from external suppliers. As long as possible this assessment has to be done without redoing expensive at sea experiments, but by using simulated data based upon previous experiments and/or high fidelity acoustic propagation modeling. A critical point is that UAC is likely one the most demanding applications for underwater acoustic propagation modeling. Indeed, apart from an accurate knowledge of the Signal-to-Noise ratio, the prediction and simulation of the UAC channel require a comprehensive modeling of the its time and spatial fluctuations (UAC channel modeled as a doubly dispersive Ricean channel). Constraints on the equipments (e.g. rms and peak transmitted power) have also to be taken into account. Specific tools which address the above aspects will be presented, from the computation of Shannon channel capacity under the above assumptions to high fidelity simulations tools relying on an explicit modeling of scattering of sound by the moving rough sea surface (e.g. NARCISSUS [1] developed by TUS). Emphasis will finally be laid upon a new innovative stochastic replay technique [2], which consists in simulating a random channel whose response has exactly the same statistical properties as a previously at sea recorded channel response, thus allowing perfect comparison of different modulation schemes or trimmings under the same environmental conditions

Simulation de canaux acoustiques sous-marins par rejeu stochastique paramétrique

National audienceContrairement au domaine des radio-communications, il n'existe pas de modèles standardisés pour simuler le canal de communication acoustique sous-marin (ASM). Cet article présente une méthodologie de simulation qui combine une modélisation paramétrique avec un rejeu stochastique de réponses impulsionnelles mesurées en mer. A partir d'une minimisation de l'entropie relative entre la réponse impulsionnelle du canal variant dans le temps mesuré et celui simulé, le principe consiste à distordre délibérément les statistiques du canal d'origine afin de répondre à certaines contraintes spécifiées par l'utilisateur. Une telle approche est bénéfique pour tester la robustesse des liens de communication acoustiques