Archives Ouvertes HAL

Toutes les publications de l'ENAC en direct.
All ENAC publications.

[hal-01496285] Circular formation control of fixed-wing UAVs with constant speeds

Publications ENAC - Mercredi, 29 mars 2017 - 15:50:52
In this paper we propose an algorithm for stabilizing circular formations of fixed-wing UAVs with constant speeds. The algorithm is based on the idea of tracking circles with different radii in order to control the inter-vehicle phases with respect to a target circumference. We prove that the desired equilibrium is exponentially stable and thanks to the guidance vector field that guides the vehicles, the algorithm can be extended to other closed trajectories. One of the main advantages of this approach is that the algorithm guarantees the confinement of the team in a specific area, even when communications or sensing among vehicles are lost. We show the effectiveness of...

[hal-01496280] Distributed algorithm for controlling scale-free polygonal formations

Publications ENAC - Mercredi, 29 mars 2017 - 15:49:24
This paper presents a distributed algorithm for controlling the deployment of a team of mobile agents in formations whose shapes can be characterized by a broad class of polygons, including regular ones, where each agent occupies a corner of the polygon. The algorithm shares the appealing properties of the popular distance-based rigid formation control, but with the additional advantage of requiring the control of fewer pairs of neighboring agents. Furthermore, the scale of the polygon can be controlled by only one pair of neighboring agents. We also exploit the exponential stability of the controlled formation in order to steer the formation as a whole with translations...

[hal-01429728] A Framework for Wind Sensitivity Analysis for Trajectory Tracking

Publications ENAC - Lundi, 27 mars 2017 - 13:26:58
In this paper a sensitivity analysis of trajectories w.r.t. wind effects is proposed. This analysis will allow to specify wind estimates properties as well as control reactiveness characteristics to ensure accurate guidance in real atmosphere. The mathematic model developed for flight dynamics is intended to take into account wind gust effects on AoA, sideslip angle and airspeed. A two layer Nonlinear Dynamic Inversion (NDI) structure has been considered to control fast and slow dynamics. In order to test the proposed approach, a full six degrees of freedom Matlab model with trained Neural Networks to emulate a Boeing 737-200 was developed.

[hal-01493782] Bayesian sparse estimation of migrating targets in autoregressive noise for wideband radar

Publications ENAC - Jeudi, 23 mars 2017 - 02:05:13
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.

[hal-01490632] Heads or tails in zero gravity: an example of a classical contextual "measurement

Publications ENAC - Jeudi, 23 mars 2017 - 02:00:55
Playing the game of heads or tails in zero gravity demonstrates that there exists a contextual "measurement" in classical mechanics. When the coin is flipped, its orientation is a continuous variable. However, the "measurement" that occurs when the coin is caught by clapping two hands together gives a discrete value (heads or tails) that depends on the context (orientation of the hands). It is then shown that there is a strong analogy with the spin measurement of the Stern-Gerlach experiment, and in particular with Stern and Gerlach’s sequential measurements. Finally, we clarify the analogy by recalling how the de Broglie-Bohm interpretation simply...

[hal-01492702] Formulation relaxée de la séparation équilibrée d’un graphe

Publications ENAC - Mercredi, 22 mars 2017 - 16:18:43
Dans ce travail, nous nous intéressons à la formulation de variantes du problème du séparateur dans un graphe (VSP , pour Vertex Separator Problem), permettant de fournir des méthodes alternatives aux méthodes classiques de clustering

[hal-01491205] A maximum likelihood-based unscented Kalman filter for multipath mitigation in a multi-correlator based GNSS receiver

Publications ENAC - Mardi, 21 mars 2017 - 02:01:09
In complex environments, the presence or absence of multipath signals not only depends on the relative motion between the GNSS receiver and navigation satellites, but also on the environment where the receiver is located. Thus it is difficult to use a specific propagation model to accurately capture the dynamics of multipath signal parameters when the GNSS receiver is moving in urban canyons or other severe obstructions. This paper introduces a statistical model for the line-of-sight and multipath signals received by a GNSS receiver. A multi-correlator based GNSS receiver is also exploited with the advantage to fully characterizing the impact of multipath signals on the...

[hal-01490737] Introduction to the Issue on Stochastic Simulation and Optimization in Signal Processing

Publications ENAC - Samedi, 18 mars 2017 - 02:09:22
The papers in this special issue seek to report cutting edge research on stochastic simulation and optimisation methodologies, and their application to challenging SP problems that are not well addressed by existing methodologies.

[hal-01486832] Convolutional Trees for Fast Transform Learning

Publications ENAC - Mardi, 14 mars 2017 - 02:09:42
—Dictionary learning is a powerful approach for sparse representation. However, the numerical complexity of classical dictionary learning methods restricts their use to atoms with small supports such as patches. In a previous work, we introduced a model based on a composition of convolutions with sparse kernels to build large dictionary atoms with a low computational cost. The subject of this work is to consider this model at the next level, i.e., to build a full dictionary of atoms from convolutions of sparse kernels. Moreover, we further reduce the size of the representation space by organizing the convolution kernels used to build atoms into a tree structure. The...

[hal-01486838] Learning a fast transform with a dictionary

Publications ENAC - Mardi, 14 mars 2017 - 02:09:42
— A powerful approach to sparse representation, dictionary learning consists in finding a redundant frame in which the representation of a particular class of images is sparse. In practice, all algorithms performing dictionary learning iteratively estimate the dictionary and a sparse representation of the images using this dictionary. However, the numerical complexity of dictionary learning restricts its use to atoms with a small support. A way to alleviate these issues is introduced in this paper, consisting in dictionary atoms obtained by translating the composition of K convolutions with S-sparse kernels of known support. The dictionary update step associated with...
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