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International audience; A comprehensive approach is developed for the simulation of single particle displacement damage in silicon. The first step corresponding to Monte Carlo simulation of the primary interaction is presented.

International audience; The TID hardness of digital color CMOS camera-on-a-chip building blocks (radiation hardened pixel array, color filter arrays and radiation hardened column ADCs) is demonstrated in the multi-MGy range using Co-60 irradiations

Faster-than-Nyquist signalization allows for a better spectral efficiency at the expense of an increased complexity. Regarding multicarrier communications, previous work mainly relied on the study of non-linear systems exploiting coding and/or equalization techniques, with no particular optimization regarding the linear part of the system. In this paper, we analyse the behavior of the optimal linear multicarrier system when used with non-linear receiving structures (iterative decoding and direct feedback equalization), or in a standalone fashion. We also investigate the limits of the assumptions commonly made for the implementation of such non-linear systems. The use of this optimal linear system allows for a closed-form expression of the bit-error probability which can be used to predict the performances and help the design of coded systems. Our work also highlights the great performance/complexity trade-off offered by decision feedback equalization in a faster-than-Nyquist context., Les communications au delà de la cadence de Nyquist permettent une augmentation de l'efficacité spectrale en contre-partie d'une complexité plus élevée. Concernant les communications multiporteuses, les travaux menés jusque là se sont principalement focalisés sur l'étude des systèmes non-linéaires exploitant des techniques de codage et/ou d'égalisation, sans considération ou optimisation particulière de la partie linéaire du système. Dans cet article, nous analysons le compor-tement du système linéaire multiporteuse optimal lorsqu'il est utilisé seul ou avec des structures de réception non-linéaires (décodage itératif et égalisation à retour de décision). Nous nous intéressons également aux limites des hypothèses com-munément utilisées lors de l'implémentation de ces systèmes non-linéaires. L'utilisation du système linéaire optimal permet une expression analytique de la probabilité d'erreur qui peut être utilisée pour prédire les performances et aider la conception de systèmes codés. Ce travail met aussi en avant le bon compromis performances/complexité offert par l'égaliseur à retour de décision dans le contexte des communications au-delà de la cadence de Nyquist.

International audience; The dark current produced by neutron irradiation in CMOS Image Sensors (CIS) is investigated. Several CIS with different photodiode types and pixel pitches are irradiated with various neutron energies and fluences to study the influence of each of these optical detector and irradiation parameters on the dark current distribution. An empirical model is tested on the experimental data and validated on all the irradiated optical imagers. This model is able to describe all the presented dark current distributions with no parameter variation for neutron energies of 14 MeV or higher, regardless of the optical detector and irradiation characteristics. For energies below 1 MeV, it is shown that a single parameter has to be adjusted because of the lower mean damage energy per nuclear interaction. This model and these conclusions can be transposed to any silicon based solid-state optical imagers such as CIS or Charged Coupled Devices (CCD). This work can also be used when designing an optical imager instrument, to anticipate the dark current increase or to choose a mitigation technique.

International audience; A multicarrier signal can be seen as a Gabor family whose coefficients are the symbols to be transmitted and whose generators are the time-frequency shifted pulse shapes to be used. In this article, we consider the case where the signaling density is increased such that inter-pulse interference is unavoidable. Such an interference is minimized when the Gabor family used is a tight frame. We show that, in this case, interference can be approximated as an additive Gaussian noise. This allows us to compute theoretical and simulated bit-error-probability for a non-coded system using a quadrature phase-shift keying constellation. Such a characterization is then used in order to predict the convergence of a coded system using low-density parity check codes. We also study the robustness of such a system to errors on the received bits in an interference cancellation context.

International audience; The performance of most direction of arrival (DoA) estimation algorithms is driven by two different kinds of errors: small, local errors in the main lobe and possibly large errors due to sidelobe peaks ambiguities. Reducing these two kinds of errors simultaneously is not possible and therefore a compromise has to be made. Motivated by automotive applications with small arrays, we consider solving this tradeoff by modifying the positions of the sensors of the array. In this letter, two new criteria are proposed to solve the above mentioned tradeoff. Optimal solutions are derived and illustrations are provided with a 3-element non-uniform linear array.

Expected likelihood (EL) technique for quality assessment of parameter estimates of signals embedded in Gaussian noise is extended in this paper over the case where useful signals are immersed in a mixture of compound Gaussian and Gaussian-distributed noises. The main problem here is that analytical expressions for distributions of such mixtures do not exist in most cases. Moreover, in some cases like $K$ -distributed noise only, where closed-form expressions for the data distribution are available, the traditional Cramér-Rao bound does not exist. This makes the EL technique even more important for parameter estimation performance assessment. In this paper, for the so-called conditional model, we introduce test statistics whose distribution for the true (actual) parameters does not depend on these parameters and specifics of texture distribution, which makes them applicable for EL applications. We illustrate the utility of this EL technique by studying and predicting the performance breakdown of some direction of arrival estimators in a mixture of $K$-distributed and Gaussian noise. Refereed/Peer-reviewed

International audience; The dark current spectroscopy is tested on twenty CMOS image sensors irradiated with protons, neutrons and various ions at different energies. The aim of this work is to differentiate the effect of coulomb and nuclear interactions on the radiation-induced dark current distribution and to identify the main radiation-induced defects responsible for the dark current increase for each type of interaction. For low-energy protons and low-energy light ions (which produce well-separated low energy coulomb interactions), we find that most of the pixels belong to a quantized dark current spectrum at low dark current. In these pixels, the dark current increase seems mainly dominated by specific point defects such as the divacancy and the vacancy-phosphorus complex. Thus, these simple defects seem to form when the displacement damage is rather low and sparse. On the contrary, for nuclear interactions (with neutrons or high-energy protons) producing high coulomb NIEL silicon PKAs or for low energy heavy ions (also having high coulomb NIEL), the DCS spectrum is not visible and all the pixels belong to an exponential hot pixel tail which extends to very high dark current. In these pixels, the dark current increase is mainly dominated by defects with close-to-midgap energy levels. These defects seem more complex than point defects because they can have many different generation rates (explaining the smooth hot pixel tail) and because they tend to form when the displacement damage is high and dense.

International audience; Faster-than-Nyquist signalization enables a better spectral efficiency at the expense of an increased computational complexity. Regarding multicarrier communications, previous work mainly relied on the study of non-linear systems exploiting coding and/or equalization techniques, with no particular optimization of the linear part of the system. In this article, we analyze the performance of the optimal linear multicarrier system when used together with non-linear receiving structures (iterative decoding and direct feedback equalization), or in a standalone fashion. We also investigate the limits of the normality assumption of the interference, used for implementing such non-linear systems. The use of this optimal linear system leads to a closed-form expression of the bit-error probability that can be used to predict the performance and help the design of coded systems. Our work also highlights the great performance/complexity trade-off offered by decision feedback equalization in a faster-than-Nyquist context.; Les communications au-delà de la cadence de Nyquist permettent une augmentation de l'efficacité spectrale en contrepartie d'une complexité plus élevée. Concernant les communications multiporteuses, les travaux menés jusque-là se sont principalement focalisés sur l'étude des systèmes non linéaires exploitant des techniques de codage et/ou d'égalisation, sans considération ou optimisation particulière de la partie linéaire du système. Dans cet article, nous analysons le comportement du système linéaire multiporteuse optimal lorsqu'il est utilisé seul ou avec des structures de réception non linéaires (décodage itératif et égalisation à retour de décision). Nous nous intéressons également aux limites de l'hypothèse de normalité de l'interférence, laquelle est utilisée lors de l'implémentation de ces systèmes non linéaires. L'utilisation du système linéaire optimal permet d'obtenir une expression analytique de la probabilité d'erreur, laquelle peut alors être utilisée pour prédire les performances et aider à la conception de systèmes codés. Ce travail met aussi en avant le bon compromis performances/complexité offert par l'égaliseur à retour de décision dans le contexte des communications au-delà de la cadence de Nyquist.

International audience; Acoustic and gravity waves propagating in planetary atmospheres have been studied intensively as markers of specific phenomena such as tectonic events or explosions or as contributors to atmosphere dynamics. To get a better understanding of the physics behind these dynamic processes, both acoustic and gravity waves propagation should be modelled in a 3D attenuating and windy atmosphere extending from the ground to the upper thermosphere. Thus, in order to provide an efficient numerical tool at the regional or global scale we introduce a finite difference in the time domain (FDTD) approach that relies on the linearized compressible Navier-Stokes equations with a background flow (wind). One significant benefit of such a method is its versatility because it handles both acoustic and gravity waves in the same simulation, which enables one to observe interactions between them. Simulations can be performed for 2D or 3D realistic cases such as tsunamis in a full MSISE-00 atmosphere or gravity-wave generation by atmospheric explosions. We validate the computations by comparing them to analytical solutions based on dispersion relations in specific benchmark cases: an atmospheric explosion, and a ground displacement forcing.

In the frame of digital video broadcasting by satellite - second generation (DVB-S2), a faster-than-Nyquist (FTN) system based on turbo equalization and low-density parity-check (LDPC) codes is proposed. Truncated maximum a posteriori (MAP) and minimum mean square error (MMSE) equalizers provide a reduced complexity implementation of the FTN system. On the other hand, LDPC codes allow us to demonstrate attractive performance results over an additive white Gaussian noise (AWGN) channel while increasing spectral efficiency beyond the Nyquist rate up to 60 % and keeping a complexity comparable to a current DVB-S2 modem.

In this article, microwave signal generation is implemented by using the optical injection locking technique. Two semiconductor laser sources are used: a Fabry-Perot laser is mode-locked to a single mode Vertical-Cavity Surface Emitting Laser (VCSEL).

International audience; In statistical signal processing, hybrid parameter estimation refers to the case where the parameters vector to estimate contains both deterministic and random parameters. Lately computationally tractable hybrid Cramér-Rao lower bounds for discrete-time Markovian dynamic systems depending on unknown time invariant deterministic parameters has been released. However in many applications (radar, sonar, telecoms, ...) the unknown deterministic parameters of the measurement model are time variant which prevents from using the aforementioned bounds. It is therefore the aim of this communication to tackle this issue by introducing new computationally tractable hybrid Cramér-Rao lower bounds.

International audience; As CMOS image sensors become more and more attractive and with high performances, it becomes possible to use CCD on CMOS devices with reasonable lengths. However, no study has been done on the radiation hardness of such CCD on CMOS devices. Therefore, we propose in this paper a first study of Charge Transfer Inefficiency (CTI) and dark current degradation under TID and DDD irradiations. To do so, test chips have been processed in conventional deep submicron CMOS imaging technologies, and characterized before and after irradiations.

International audience; A Radiation Hard CMOS Active Pixel Image Sensor has been designed, manufactured and exposed to X and 60Co γ-ray sources up to several MGy of Total Ionizing Dose (TID). It is demonstrated that a Radiation-Hardened-By-Design (RHBD) CMOS Image Sensor (CIS) can still provide useful images after 10 MGy(SiO2) (i.e. 1 Grad). This paper also presents the first detailed characterizations of CIS opto-electrical performances (i.e. dark current, quantum efficiency, gain, noise, transfer functions, etc.) in the MGy range. These results show that it is possible to design a CIS with good performances even after having absorbed several MGy. Four different RHBD photodiode designs are compared: a standard photodiode design, two well known RHBD layouts and a proposed improvement of the gated photodiode design. The proposed layout exhibits the best performances over the entire studied TID range and further optimizations are discussed. Several original MGy radiation effects are presented and discussed at the device and circuit levels and mitigation techniques are proposed to improve further the radiation hardness of future Rad-Hard CIS developments for extreme TID applications (e.g. for nuclear power plant monitoring/dismantling, experimental reactors (e.g. ITER) or next generation particle physics experiments (e.g. CERN)).

This letter investigates hybrid lower bounds on the mean square error in order to predict the so-called threshold effect. A new family of tighter hybrid large error bounds based on linear transformations (discrete or integral) of a mixture of the McAulay–Seidman bound and the Weiss–Weinstein bound is provided in multivariate parameters case with multiple test points. For use in applications, we give a closed-form expression of the proposed bound for a set of Gaussian observation models with parameterized mean, including tones estimation which exemplifies the threshold prediction capability of the proposed bound.

This letter deals with the problem of fluctuating target detection in heavy-tailed $K$-distributed clutter over a number $T$ of independent coherent intervals, e.g., in the case of a long observation interval (``stare mode''), or that of independent (range) resolution cells as per the track before detect techniques. The generalized likelihood ratio test for the problem at hand is derived, as well as an approximation of it, whose distribution under the null hypothesis is derived. We also show some significant differences as compared to the usual Gaussian case, in particular the influence of $T$ and of the shape parameter of the $K$ distribution.

National audience

Dark Current Spectroscopy (DCS) is tested for the first time on irradiated Pinned PhohoDiode (PPD) CMOS Image sensors (CIS) to detect and identify radiation-induced silicon bulk defects in the depleted volume of the pixels. Two different CIS are tested: a 5MP Commercial-Off-The-Shelf (COTS) CIS from OmniVision (OV5647) and a 256x256 pixels custom CIS. These CISs are irradiated with alpha particles at various fluences and two different particle energies are tested on the custom CIS (4 MeV and < 500 keV). Several types of defects are detected in both CIS (up to five defects in the custom CIS). The dark current is measured at various temperatures to extract the activation energy and deduce the energy levels of the defects. The defect formation rate per unit fluence is calculated. In the custom CIS, the annealing behavior of the defects is also studied by performing an isochronal annealing. Two different defects are identified: the divacancy and the vacancy-phosphorus. This work proves that the DCS technique can be used on irradiated CIS to detect and identify radiation-induced defects in silicon.

Seismic shaking is an attractive mechanism to explain the destabilisation of regolith slopes and the regolith migration found on the surfaces of asteroids (Richardson et al. 2004; Miyamoto et al. 2007). Here, we use a continuum mechanics method to simulate the seismic wave propagation in an asteroid. Assuming that asteroids can be described by a cohesive core surrounded by a thin non-cohesive regolith layer, our numerical simulations of vibrations induced by micro-meteoroids suggest that the surface peak ground accelerations induced by micro-meteoroid impacts may have been previously under-estimated. Our lower bound estimate of vertical accelerations induced by seismic waves is about 50 times larger than previous estimates. It suggests that impact events triggering seismic activity are more frequent than previously assumed for asteroids in the kilometric and sub-kilometric size range. The regolith lofting is also estimated by a first order ballistic approximation. Vertical displacements are small, but lofting times are long compared to the duration of the seismic signals. The regolith movement has a non-linear dependence on the distance to the impact source which is induced by the type of seismic wave generating the first movement. The implications of regolith concentration in lows of surface acceleration potential are also discussed. We suggest that the resulting surface thermal inertia variations of small fast rotators may induce an increased sensitivity of these objects to the Yarkovsky effect., Accepted for publication in Icarus

We consider the problem of estimating the direction of arrival of a signal embedded in $K$-distributed noise, when secondary data which contains noise only are assumed to be available. Based upon a recent formula of the Fisher information matrix (FIM) for complex elliptically distributed data, we provide a simple expression of the FIM with the two data sets framework. In the specific case of $K$-distributed noise, we show that, under certain conditions, the FIM for the deterministic part of the model can be unbounded, while the FIM for the covariance part of the model is always bounded. In the general case of elliptical distributions, we provide a sufficient condition for unboundedness of the FIM. Accurate approximations of the FIM for $K$-distributed noise are also derived when it is bounded. Additionally, the maximum likelihood estimator of the signal DoA and an approximated version are derived, assuming known covariance matrix: the latter is then estimated from secondary data using a conventional regularization technique. When the FIM is unbounded, an analysis of the estimators reveals a rate of convergence much faster than the usual $T^{-1}$. Simulations illustrate the different behaviors of the estimators, depending on the FIM being bounded or not., 25 pages, 8 figures, submitted to IEEE Transactions Signal Processing

International audience; Total ionizing dose (TID) effects are studied for a long time in micro-electronic components designed to operate in natural and artificial environments. In most cases, TID induces both charge trapping in the bulk of irradiated oxides and the buildup of interface traps located at semiconductor/dielectric interfaces. Such effects result from basic mechanisms driven by both the shape of the electric field which stands into the oxide and of its fabrication process parameters which define pre-existing traps in the oxide’s bulk. From the pioneering studies based on “thick” oxides technologies to the most recent ones dedicated to innovative technologies, most of them concluded that the impact of total ionizingdose effects reduces with thinning the oxides. This is specifically the case for the gate-oxide of Metal-Oxide-Semiconductor Field Effect Transistors (MOSFET) for which it is generally considered that TID is not anymore a major issue at kGy dose ranges. TID effects are now mainly due to charge trapping in the field oxides such as Shallow Trench Isolation. This leads to create either parasitic conduction paths or to Radiation-Induced Narrow Channel Effects (RINCE). Static current-voltage (I-V) electrical characteristics are then modified through a significant increase of the off-current of NMOS transistors or by shifting the whole I-V curves (of both NMOS and PMOS transistors) respectively. Based on these assumptions, no significant shift of I-V curves should be observed in modern bulk CMOS technologies.However, this paper presents evidences of large threshold voltage shifts measured at MGy dose levels despite the fact that transistors are designed in a submicron bulk technology which features a 7-nm thin gate-oxide. These electrical shifts are encountered on PMOS transistors of different widths, WNARROW = 0.24 μm and WWIDE = 10 μm. The devices are irradiated using 10 keV X-rays at several total dose steps up to 3 MGy. On the one hand, negative threshold voltage shifts of more than 3.3 V are extracted after 3 MGy on narrow transistors. Even very high, this voltage shift is consistent with RINCE in narrow open layout transistors. On the other hand, voltage shifts greater than 2.5 V are extracted on wide transistors. Obviously, this result should not be associated neither to positive charge trapping in the thin gate oxide nor to any RINCE in this very wide transistor geometry.The final paper will thus provide an extensive study of this effect using other device designs and geometries tested with dedicated TID experiments to discuss whether or not this effect revealed at very high TID, i.e. several MGy, may be attributed to an enhanced high-TID induced charge trappingmechanism in thin gate oxides.

International audience; This study presents an analytical model of the Full Well Capacity(FWC) in Pinned Photodiode (PPD) CMOS image sensors. By introducing the temperature dependence of the PPD pinning voltage, the existing model is extended (with respect to previous works) to take into account the effect of temperature on the FWC. It is shown, with the support of experimental data, that whereas in dark conditions the FWC increases with temperature, a decrease is observed if FWC measurements are performed under illumination. This study also shows that after a light pulse, the charge stored in the PPD drops as the PPD tends toward equilibrium. On the base of these observations, an analytical model of the dynamic behaviour of the FWC in non-continuous illumination conditions is proposed. The model is able to reproduce experimental data over six orders of magnitude of time. Both the static and dynamic models can be useful tools to correctly interpret FWC changes following design variations and to accurately define the operating conditions during device characterizations.

This presentation provides an overview of Total Ionizing Dose effects in CMOS bulk and SOI technologies. The particular case of hardening-by-design of a CMOS imager for the MGy range is used as a practical example to illustrates the presented degradation mechanisms.

International audience; There is an increasing interest in developing cameras for surveillance systems to monitor nuclear facilities or nuclear waste storages [1]. Particularly, for today’s and the next generation of nuclear facilities increasing safety requirements consecutive to Fukushima Daiichi’s disaster have to be considered. For some applications, radiation tolerance needs to overcome doses in the MGy(SiO2) range whereas the most tolerant commercial or prototypes products based on solid state image sensors withstand doses up to few kGy [2]. The objective of this work is to present the radiation hardening strategy developed by our research groups to enhance the tolerance to ionizing radiations of the various subparts of these imaging systems by working simultaneously at the component and system design levels.Developing radiation-hardened camera implies to combine several radiation-hardening strategies. In our case, we decided not to use the simplest one, the shielding approach. This approach is efficient but limits the camera miniaturization and is not compatible with its future integration in remote-handling or obotic systems. Then, the hardening-by-component strategy appears mandatory to avoid the failure of one of the camera subparts at doses lower than the MGy.Concerning the image sensor itself, the used technology is a CMOS Image Sensor (CIS) designed by ISAE team with custom pixel designs used to mitigate the total ionizing dose (TID) effects that occur well below the MGy range in classical image sensors (e.g. Charge Coupled Devices (CCD), Charge Injection Devices (CID) and classical Active Pixel Sensors (APS)), such as the complete loss of functionality, the dark current increase and the gain drop. We’ll present at the conference a comparative study between these radiation-hardened pixel radiation responses with respect to conventional ones, demonstrating the efficiency of the choices made. The targeted strategy to develop the complete radiation hard camera electronics will be exposed. Another important element of the camera is the optical system that transports the image from the scene to the image sensor. This arrangement of glass based lenses is affected by radiations through two mechanisms: the radiation induced absorption andthe radiation induced refractive index changes. The first one will limit the signal to noise ratio of the image whereas the second one will directly affect the resolution of the camera. We’ll present at the conference a coupled simulation/experiment study of these effects for various commercial glasses and present vulnerability study of typical optical systems to radiations at MGy doses. The last very important part of the camera is the illumination system that can be based on various technologies of emitting devices like LED, SLED or lasers. The most promising solutions for high radiation doses will be presented at the conference.In addition to this hardening-by-component approach, the global radiation tolerance of the camera can be drastically improve by working at the system level, combining innovative approaches eg. for the optical and illumination systems. We’ll present at the conference the developed approach allowing to extend the camera lifetime up to the MGy dose range.[1] Cho, Jai Wan; Choi, Young Soo; Jeong, Kyung Min, “Monitoring Performance of the Cameras under the High Dose-Rate Gamma Ray Environments”, Health Physics:May 2014 - Volume 106 - Issue 5 - pS47-S58[2] Armani, J.M., Barrochin, P. ; Joffre, F. ; Gaillard, R. ; Saigne, F. ; Mainguy, J.L., “Enhancement of the total dose tolerance of a commercial CMOS active pixel sensor by use of thermal annealing”, Radiation and Its Effects on Components and Systems (RADECS 2011 Proceedings), pp. 340-344,2011.

We report seismic signals on a desert playa caused by convective vortices and dust devils. The long-period (10-100s) signatures, with tilts of ~10$^{-7}$ radians, are correlated with the presence of vortices, detected with nearby sensors as sharp temporary pressure drops (0.2-1 mbar) and solar obscuration by dust. We show that the shape and amplitude of the signals, manifesting primarily as horizontal accelerations, can be modeled approximately with a simple quasi-static point-load model of the negative pressure field associated with the vortices acting on the ground as an elastic half space. We suggest the load imposed by a dust devil of diameter D and core pressure {\Delta}Po is ~({\pi}/2){\Delta}PoD$^2$, or for a typical terrestrial devil of 5 m diameter and 2 mbar, about the weight of a small car. The tilt depends on the inverse square of distance, and on the elastic properties of the ground, and the large signals we observe are in part due to the relatively soft playa sediment and the shallow installation of the instrument. Ground tilt may be a particularly sensitive means of detecting dust devils. The simple point-load model fails for large dust devils at short ranges, but more elaborate models incorporating the work of Sorrells (1971) may explain some of the more complex features in such cases, taking the vortex winds and ground velocity into account. We discuss some implications for the InSight mission to Mars., Comment: Contributed Article for Bulletin of the Seismological Society of America, Accepted 29th August 2015

Asteroids and other Small Solar System Bodies (SSSBs) are currently of great scientific and even industrial interest. Asteroids exist as the permanent record of the formation of the Solar System and therefore hold many clues to its understanding as a whole, as well as insights into the formation of planetary bodies. Additionally, SSSBs are being investigated in the context of impact risks for the Earth, space situational awareness and their possible industrial exploitation (asteroid mining). In all these aspects, the knowledge of the geophysical characteristics of SSSB surface and internal structure are of great importance. Given their size, constitution, and the evidence that many SSSBs are not simple monoliths, these bodies should be studied and modelled as self-gravitating granular systems in general, or as granular systems in micro-gravity environments in particular contexts. As such, the study of the geophysical characteristics of SSSBs is a multi-disciplinary effort that lies at the crossroads between Granular Mechanics, Celestial Mechanics, Soil Mechanics, Aerospace Engineering and Computer Sciences. The authors acknowledge support by the International Space Science Institute (ISSI, Bern, Switzerland) and Paris observatory (France) to the international team «Asteroids & Self-Gravitating Bodies as Granular Systemsa». EO acknowledges European Space Agency program SpaceGrains and Prodex (Belspo, Brussels, Belgium) for financial support.

International audience; Multicarrier transmissions are classically based on undercomplete or exact Weyl–Heisenberg Riesz (biorthogonal or orthogonal) bases implemented thanks to oversampled filter-banks. This can be seen as a transmission below the Nyquist rate. However, when overcomplete Weyl–Heisenberg frames are used, we obtain a " faster-than-Nyquist " (FTN) system and it is theoretically impossible to recover exactly transmitted symbols using a linear receiver. Various studies have shown the interest of this high density signaling scheme as well as practical implementations based on trellis and/or iterative decoding. Nevertheless, there is still a lack of theoretical justifications with regard to pulse design in the FTN case. In this paper, we consider a linear transceiver operating over an additive white Gaussian noise channel. Using the frame theory and simulation results, we show that the mean squared error (MSE) is minimized when tight frames are used.

International audience; Wideband radar systems are highly resolved in range, which is a desirable feature for mitigating clutter. However, due to a smaller range resolution cell, moving targets are prone to migrate along the range during the coherent processing interval (CPI). This range walk, if ignored, can lead to huge performance degradation in detection. Even if compensated, conventional processing may lead to high sidelobes preventing from a proper detection in case of a multitarget scenario. Turning to a compressed sensing framework, we present a Bayesian algorithm that gives a sparse representation of migrating targets in case of a wideband waveform. Particularly, it is shown that the target signature is the sub-Nyquist version of a virtually well-sampled two-dimensional (2D)-cisoid. A sparse-promoting prior allows then this cisoid to be reconstructed and represented by a single peak without sidelobes. Performance of the proposed algorithm is finally assessed by numerical simulations on synthetic and semiexperimental data. Results obtained are very encouraging and show that a nonambiguous detection mode may be obtained with a single pulse repetition frequency (PRF).

International audience; In this paper we address the problem of fundamental limitations on resolution in deterministic parameters estimation. We introduce a definition of resolvability based on probability and incorporating a requirement for accuracy unlike most existing definitions. Indeed in many application the key problem is to obtain distributions of estimates that are not only distinguishable but also accurate and compliant with a required precision. We exemplify the proposed definition with estimators that produce normal estimates, as in the conditional model for which the Gaussianity and efficiency of maximum likelihood estimators (MLEs) in the asymptotic region of operation (in terms of signal-to-noise ratio and/or in large number of snapshots) is well established, even for a single snapshot. In order to measure the convergence in distribution, we derive a simple test allowing to check whether the conditional MLEs operate in the asymptotic region of operation. Last, we discuss the resolution of two complex exponentials with closely spaced frequencies and compare the results obtained with the ones provided by the various statistical resolution limit released in the open literature.

International audience; An experimental method using a CMOS image sensor as test device is proposed to study the kinetics of formation and annealing of Single Particle Displacement Damage (SPDD) events in arrays of silicon microvolumes. The dark current level is monitored in real time under neutron irradiation, allowing to detect SPDD events and follow their subsequent annealing behavior. Both short term and long term annealing results are presented, with recordings from 75 ms to 4.5 days after SPDD events, performed with different integration times. A majority of pixels exhibits a continuous logarithmic relaxation; a selection of particular cases is finally presented, corresponding to pixels exhibiting Random Telegraph Signals.

International audience; In recent work we showed the interest of using sparse representation techniques to estimate a target scene observed by wideband radar systems. However the principle was demonstrated in a white noise background only. In this paper, we present an extended version of our sparse estimation technique that attempts to take into account the (possible) presence of diffuse clutter. More specifically, an autoregressive model is considered for the noise vector. Performance of the technique is studied on synthetic and experimental data. Pertinence of the noise model is discussed.

A set of seven caged gadolinium complexes were used as vectors for introducing the chelated Gd3+ ion into protein crystals in order to provide strong anomalous scattering for de novo phasing. The complexes contained multidentate ligand molecules with different functional groups to provide a panel of possible interactions with the protein. An exhaustive crystallographic analysis showed them to be nondisruptive to the diffraction quality of the prepared derivative crystals, and as many as 50% of the derivatives allowed the determination of accurate phases, leading to high-quality experimental electron-density maps. At least two successful derivatives were identified for all tested proteins. Structure refinement showed that the complexes bind to the protein surface or solvent-accessible cavities, involving hydrogen bonds, electrostatic and CH-π interactions, explaining their versatile binding modes. Their high phasing power, complementary binding modes and ease of use make them highly suitable as a heavy-atom screen for high-throughput de novo structure determination, in combination with the SAD method. They can also provide a reliable tool for the development of new methods such as serial femtosecond crystallography. © 2014 International Union of Crystallography.

International audience; The characterization of GNSS position errors in urban environments is an important issue for integrity monitoring and classification of receivers’ performance. However, these errors are not observable directly by the receiver, therefore RAIM methods use statistics based on the pseudorange residuals (i.e. observable errors). In this work, we focus on the modelling and analysis of navigation errors in the position-domain rather than individual range-domain errors that are difficult to model in urban environments due to multipath and non-line-of-sight (NLOS) signals. Using a trajectory of reference we compute the horizontal position errors (HPE) and its non-parametric distribution function given by the empirical Cumulative Distribution Function (CDF). According to the results, we observe that these errors have a heavy-tailed distribution, and then we propose to fit the empirical CDF with the CDF of the generalized Pareto distribution (GPD). We use an inflated version of the fitted Pareto model to overbound the CDF of the HPE for the calculation of Horizontal Protection Level (HPL), i.e., bounding the radial position errors.

International audience; This paper focuses on the Dark Current-Random Telegraph Signal (DC-RTS) in solid-state image sensors. The DC-RTS is investigated in several bulk materials, for different surface interfaces and for different trench isolation interfaces. The main parameter used to characterize the DC-RTS is the transition maximum amplitude which seems to be the most appropriate for studying the phenomenon and identifying its origin. Proton, neutron and Co-60 Gamma-ray irradiations are used to study DC-RTS induced by both Total Ionizing Dose (TID) and Displacement damage (Dd) dose. Conclusions are drawn by analyzing the correlation between the exponential slope of the transition maximum amplitude histogram and the location of the DC-RTS-induced defects. The presented results can be extrapolated to predict DC-RTS distributions in various kinds of solid state image sensors.

In this letter, we consider two sets of observations defined as subspace signals embedded in noise and we wish to analyze the distance between these two subspaces. The latter entails evaluating the angles between the subspaces, an issue reminiscent of the well-known Procrustes problem. A Bayesian approach is investigated where the subspaces of interest are considered as random with a joint prior distribution (namely a Bingham distribution), which allows the closeness of the two subspaces to be adjusted. Within this framework, the minimum mean-square distance estimator of both subspaces is formulated and implemented via a Gibbs sampler. A simpler scheme based on alternative maximum a posteriori estimation is also presented. The new schemes are shown to provide more accurate estimates of the angles between the subspaces, compared to singular value decomposition based independent estimation of the two subspaces., Submitted for publication in IEEE Signal Process. Letters

International audience; Reliable GNSS positioning is difficult to be achieved in dense urban areas, because in these environments typically the satellite signals are often obscured or reflected by buildings and receiver-surrounding objects to cause multipath signal reflections, which distort measurements and bias the calculated position. Diffracted and reflected signals received with the direct signal can result in ten-meter-order positioning errors, and hundreds of meters of positioning error can be present in non-line-of-sight signals (NLOS) situations. Thus, degraded receptions due to these phenomena are the dominant causes of reduced reliability in urban environments positioning. The standard way to solve the NLOS problem in GNSS receivers is to identify and exclude the associated measurements in the navigation algorithm, with techniques such as RAIM, when the induced error is not acceptable. However, this approach is not adapted to positioning in harsh environments (urban canyons, deep urban and indoor), where only few satellites in NLOS situations may be available and PVT solution has to be computed even from these degraded measurements. Under such poor conditions of satellites visibility, the positioning algorithm has to take into account the fact that the received signal may be received from a non-direct path with an additional distance. The objective of this work is to introduce a new methodology of exploiting these NLOS measurements, usually removed by GNSS receivers in good availability conditions. In traditional RAIM, a local test checks the reliability of PR measurements, and the global test checks the reliability of position solution in presence of contaminated observables. In this paper, we apply robust statistics as a powerful tool for statistical analysis in presence of outliers. However using robust tests, (e.g. robust covariance estimation), achieve their limits when most of the data resemble outliers. The robustness of a robust estimation method is measured by the breakdown point, representing the proportion of incorrect observations that this estimator can handle when computing the robust estimate [1]. The maximum breakdown point in M-estimation methods is up to 50%, thus when the percentage of biased pseudorange (PR) exceeds the half, as in urban environments, robust RAIM techniques will fail also. To overcome this issue, a realistic NLOS bias model is developed based on the predicted PRs. When the number of reliable satellites measurements is insufficient, other sources of information need to be used to increase information redundancy and improve the PVT solution. The usual approach is to use dead-reckoning sensors (IMU, odometer, etc.) together with the GNSS measurements as inputs of a fusion algorithm. They can be integrated with the GNSS to compensate the navigation error even when the PRs are not available [2]. On the other hand, the PRs can calibrate the sensor when they are available. While there are many works describing the fusion of other sensors with GNSS to improve accuracy and availability, the aspect on the reliability of the navigation solutions based on such configurations are still needed. Instead of using least square residuals as in standard RAIM we propose in this paper to estimate the size of multipath errors in the observed PR using Doppler observables and odometer measurements. The size of multipath (MP) errors is computed as the difference between observations and predicted values, then used for reliability checking and measurements error modeling. More precisely we use the odometer to predict reliable PR measurements, such that PR(t) = PR(t-1) + DeltaR, where DeltaR is computed from the odometer and satellite velocity. Then the measured PR and predicted ones will be compared using a consistency checking metric such as Kullback-Leibler Divergence that permit us to compute the adaptive variance of the PR observation from the area of PDFs overlapping [3]. Therefore, we may use the odometer error distribution to compute the error distribution of the NLOS PR which can be exploited for reliability analysis in the range domain. In other words, this scheme provides a way to correct the NLOS bias of PRs from a trusted external sensor. Reliability checking is a challenging task in harsh urban environment because modeling the GNSS errors is quite complex. The work in [4] has demonstrated that using principle component analysis (PCA) for stochastic fault detection is viable without knowing the state-model a priori. This has sparked our interest to also investigate the PR reliability checking by means of PCA in this paper. However, the PRs measurement errors in deep urban areas could be correlated and as such, PCA is not optimal in this situation. In order to overcome this limitation, the PR reliability checking is implemented using a robust PCA. A robust PCA can be obtained by robust estimation of the measurements covariance [1] and the robust residuals permit us to address the identification of the biases. In the analysis, the validity of the predicted PR values and the model of the PR prediction error are studied as a function of time using a reference trajectory system (SPAN FSAS Novatel/iMAR IMU). The NLOS PR error distribution is estimated and validated from data. The reliability checking approaches described above will be discussed and analyzed in different scenarios for evaluation using real GPS signals. In summary, this work implements robust reliability checking with robust statistics to exploit NLOS measurements which are usually removed by GNSS receivers in urban navigation. Inclusive in the study are modeling of multipath errors, RAIM with MP residuals, use of odometer to predict reliable PR measurements, and applying PCA for GNSS reliability.

International audience; Radiation effects in thick isolation oxides of modern CMOS technologies are investigated using dedicated test structures designed using two commercial foundries. Shallow Trench Isolation and Pre-Metal Dielectric are studied using electrical measurements performed after X-ray irradiations and isochronal annealing cycles. This paper shows that trapping properties of such isolation oxides can strongly differ from those of traditional thermal oxides usually used to process the gate oxide of Metal Oxide Semiconductor Field Effect Transistors. Buildup and annealing of both radiation-induced oxide-trap charge and radiation-induced interface traps are discussed as a function of the oxide type, foundry and bias condition during irradiation. Radiation-induced interface traps in such isolation oxides are shown to anneal below 100°C contrary to what is usually observed in thermal oxides. Implications for design hardening and radiation tests of CMOS Integrated Circuits are discussed.

International audience; This paper investigates the TID sensitivity of silicon-based technologies at several MGy irradiation doses to evaluate their potential for high TID-hardened circuits. Such circuits will be used in several specific applications suc as safety systems of current or future nuclear power plants considering various radiation environments including normal and accidental operating conditions, high energy physics instruments, fusion experiments or deep space missions. Various device designs implemented in well established bulk silicon and Partially Depleted SOI technologies are studied here up to 3 MGy. Furthermore, new insights are given on the vulnerability of more advanced technologies including planar Fully Depleted SOI and multiple-gate SOI transistors at such high dose. Potential of tested technologies are compared and discussed for stand-alone integrated circuits.

International audience; Space missions1, 2 and thermal infrared observations3 have shown that small asteroids (kilometre-sized or smaller) are covered by a layer of centimetre-sized or smaller particles, which constitute the regolith. Regolith generation has traditionally been attributed to the fall back of impact ejecta and by the break-up of boulders by micrometeoroid impact4, 5. Laboratory experiments6 and impact models4, however, show that crater ejecta velocities are typically greater than several tens of centimetres per second, which corresponds to the gravitational escape velocity of kilometre-sized asteroids. Therefore, impact debris cannot be the main source of regolith on small asteroids4. Here we report that thermal fatigue7, 8, 9, a mechanism of rock weathering and fragmentation with no subsequent ejection, is the dominant process governing regolith generation on small asteroids. We find that thermal fragmentation induced by the diurnal temperature variations breaks up rocks larger than a few centimetres more quickly than do micrometeoroid impacts. Because thermal fragmentation is independent of asteroid size, this process can also contribute to regolith production on larger asteroids. Production of fresh regolith originating in thermal fatigue fragmentation may be an important process for the rejuvenation of the surfaces of near-Earth asteroids, and may explain the observed lack of low-perihelion, carbonaceous, near-Earth asteroids10.

International audience; This paper investigates the vulnerability of several micro- and nano-electronic technologies to a mixed harsh environment involving high total ionizing dose at MGy levels and high temperature. Such operating conditions emerge today for several applications like new security systems in existing or future nuclear power plants, fusion experiments, or deep space missions. In this work, the competing effects of ionizing radiations and temperature are characterized in elementary devices made of MOS transistors from several technologies. First, devices are irradiated using a radiation laboratory X-ray source up to MGy dose levels at room temperature. Devices are either grounded or biased during irradiation to simulate two major circuit cases: a circuit which waits for a wake up signal, representing most of the lifetime of an integrated circuit operating in a harsh environment, and a nominal circuit function. Devices are then annealed at several temperatures to discuss the post-irradiation behavior and to determine whether an elevated temperature is an issue or not for circuit function in mixed harsh environments.

National audience; Ce papier présente la caractérisation expérimentale de l'interaction entre une onde électromagnétique RF et une micro-décharge plasma à l'aide de deux dispositifs de mesure. Ces dispositifs consistent en l'intégration d'une micro-décharge plasma au sein de différentes lignes de transmission, à savoir une ligne microruban et une ligne microruban inversée. L'influence de la microdécharge plasma sur les paramètres S est ainsi mise en évidence, et plus particulièrement certaines propriétés d'absorption mais aussi de déphasage de l'onde RF.

International audience; Reliable GNSS positioning is a very challenging task in harsh urban environment. The main source of error is due to non-line-of-sight (NLOS) reception and multipath phenomena. The effect of assuming a direct path in a NLOS propagation environment leads to serious degradation in accuracy. Instead of discarding all measurements which are found to be in NLOS conditions, we propose to properly use these observations to improve the positioning accuracy and integrity in harsh environments. In this paper, we combine the sigma-ε variance model with a mean jump (i.e. NLOS bias) to model the pseudorange (PR) errors. First, we use a 3D model of the environment to detect the NLOS state of reception and to predict the NLOS bias related to the excess delay phenomenon. For reliable positioning, we use a C/No-based variance adjustment for the LOS PRs, and we subtract the bias from the NLOS PRs during the trilateration step of position computation. The performance of the proposed scheme is assessed using real data and compared to a standard Kalman filter without predicted information from the 3D simulator.

Adaptive detection of distributed radar targets in homogeneous Gaussian noise plus subspace interference is addressed. It is assumed that the actual steering vectors lie along a fixed and unknown direction of a preassigned and known subspace, while interfering signals are supposed to belong to an unknown subspace, with directions possibly varying from one resolution cell to another. The resulting detection problem is formulated in the framework of statistical hypothesis testing and solved using an ad hoc algorithm strongly related to the generalised likelihood ratio test. A performance analysis, carried out also in comparison to natural benchmarks, is presented.

This paper analyses the performance of TCP over random and dedicated access methods in the context of DVB-RCS2. Random access methods introduce a lower connection delay compared to dedicated methods. We investigate the poten- tial to improve the performance of short flows in regards to transmission delay, over random access methods for DVB- RCS2 that is currently under development. Our simulation experiments show that the transmission of the first ten IP datagrams of each TCP flow can be 500 ms faster with ran- dom access than with dedicated access making the former of interest to carry Internet traffic. Such methods, however, are less efficient in regards to bandwidth usage than dedicated access mecanisms and less reliable in overloaded network conditions. Two aspects of channel usage optimization can be distinguished: reducing the duration of ressource utiliza- tion with random access methods, or increasing the spec- trum efficiency with dedicated access methods. This article argues that service providers may let low-cost users exploit the DVB-RCS2 to browse the web by introducing different services, which choice is based on the channel access method., Comment: ACMLCDNet 2013

International audience

International audience; A hardening method is proposed to enable the use of CMOS image sensors for Fusion by Inertial Confinement Diagnostics. The mitigation technique improves their radiation tolerance using a reset mode implemented in the device. The results obtained evidence a reduction of more than 70% in the number of transient white pixels induced in the pixel array by the mixed neutron and $gamma$ -ray pulsed radiation environment.

International audience; We present an approach coupling a limited experimental number of tests with numerical simulations regarding the design of radiation-hardened (RH) rare earth (RE)-doped fiber amplifiers. Radiation tests are done on RE-doped fiber samples in order to measure and assess the values of the principal input parameters requested by the simulation tool based on particle swarm optimization (PSO) approach. The proposed simulation procedure is validated by comparing the calculation results with the measured degradations of two amplifiers made with standard and RH RE-doped optical fibers, respectively. After validation, the numerical code is used to theoretically investigate the influence of some amplifier design parameters on its sensitivity to radiations. Simulations show that the RE-doped fiber length used in the amplifier needs to be adjusted to optimize the amplifier performance over the whole space mission profile rather than to obtain the maximal amplification efficiency before its integration in the harsh environment. By combining this coupled approach with the newly-developed RH RE-doped fibers, fiber-based amplifiers nearly insensitive to space environment may be designed in the future.

This work presents an experimental design for studying low-velocity collisions into granular surfaces in low-gravity. In the experiment apparatus, reduced-gravity is simulated by releasing a free-falling projectile into a surface container with a downward acceleration less than that of Earth's gravity. The acceleration of the surface is controlled through the use of an Atwood machine, or a system of pulleys and counterweights. The starting height of the surface container and the initial separation distance between the projectile and surface are variable and chosen to accommodate collision velocities up to 20 cm/s and effective accelerations of ~0.1 - 1.0 m/s^2. Accelerometers, placed on the surface container and inside the projectile, provide acceleration data, while high-speed cameras capture the collision and act as secondary data sources. The experiment is built into an existing 5.5 m drop-tower frame and requires the custom design of all components, including the projectile, surface sample container, release mechanism and deceleration system. Data from calibration tests verify the efficiency of the experiment's deceleration system and provide a quantitative understanding of the performance of the Atwood system., 11 pages, 11 figures

In \cite{Abramovich04}, it was demonstrated that the likelihood ratio (LR) for multivariate complex Gaussian distribution has the invariance property that can be exploited in many applications. Specifically, the probability density function (p.d.f.) of this LR for the (unknown) actual covariance matrix $\R_{0}$ does not depend on this matrix and is fully specified by the matrix dimension $M$ and the number of independent training samples $T$. Since this p.d.f. could therefore be pre-calculated for any a priori known $(M,T)$, one gets a possibility to compare the LR of any derived covariance matrix estimate against this p.d.f., and eventually get an estimate that is statistically ``as likely'' as the a priori unknown actual covariance matrix. This ``expected likelihood'' (EL) quality assessment allows for significant improvement of MUSIC DOA estimation performance in the so-called ``threshold area'' \cite{Abramovich04,Abramovich07d}, and for diagonal loading and TVAR model order selection in adaptive detectors \cite{Abramovich07,Abramovich07b}. Recently, a broad class of the so-called complex elliptically symmetric (CES) distributions has been introduced for description of highly in-homogeneous clutter returns. The aim of this report is to extend the EL approach to this class of CES distributions as well as to a particularly important derivative of CES, namely the complex angular central distribution (ACG). For both cases, we demonstrate a similar invariance property for the LR associated with the true scatter matrix $\mSigma_{0}$. More precisely, we show that the probability density function (p.d.f.) of the likelihood ratio (LR) for the (unknown) actual scatter matrix $\mSigma_{0}$ does not depend on the latter: it only depends on the density generator for the CES distribution and is distribution-free in the case of ACG distributed data, i.e., it only depends on the matrix dimension $M$ and the number of independent training samples $T$. Furthermore, we derive fixed point regularized covariance matrix estimates using the generalized expected likelihood methodology. This first chapter of this report is devoted to the conventional scenario ($T \geq M$) while Chapter 2 deals with the under-sampled scenario ($T \leq M$). Although the two parts are closely related, each one is self-contained and could be read independently.