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Conference Paper

Wing 3D Reconstruction by Constraining the Bundle Adjustment with Mechanical Limitations

Authors: Demoulin Quentin, Lefebvre-Albaret François, Basarab Adrian, Kouamé Denis and Tourneret Jean-Yves

In Proc. 28th European Signal Processing Conference (EUSIPCO), Amsterdam, Netherlands, January 18-22, 2021.

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The estimation of wing deformation is part of the certification of an aircraft. Wing deformation can be obtained from 3D reconstructions based on conventional multiview photogrammetry. However, 3D reconstructions are generally degraded by the variable flight environments that degrade the quality of 2D images. This paper addresses this issue by taking benefit from a priori knowledge of the wing mechanical behaviour. Specifically, mechanical limits are considered to regularize the bundle adjustment within the photogrammetry reconstruction. The performance of the proposed approach is evaluated on a real case, using data acquired on an aircraft A350-900.

Signal and image processing / Aeronautical communication systems

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PhD Thesis

Routeur embarqué pour les communications critiques aéronautiques en environnement multi liens

Author: Tran N'Guyen Hoang Alexandre

Defended on January 20, 2021.

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Critical aeronautical communications are a major issue for flight safety. For a long time, these have relied solely on voice, which is transmitted via an analog communication system. Given the growth in air traffic, this mean of communication has reached saturation and moreover, it has sometimes shown its limits in terms of understanding voice messages, hence the need to find an alternative method. The development of communication technologies based on digital signals allows text messages to be exchanged over a long distance. Initially reserved for noncritical airline operations, it was quickly adopted for communications between the pilot and the air traffic controller, in order to offload the dedicated radio channel. This is known as Data Link. This system, included in a more global infrastructure called the ATN/OSI, has the double advantage of relieving congestion on the frequencies used, but also of limiting the misunderstanding of certain messages. The next evolutions of this aeronautical communication system based on the IP suite and called ATN/IPS is under development. It will have to solve certain problems by proposing new communication technologies and innovative network solutions that can adapt to the increase in critical air data traffic. In this thesis, we address several issues related to the development of ATN/IPS. The first one concerns the network mobility of the aircraft. Indeed, the ATN/IPS will gather several operators, each providing their own subnetworks composed of one or more access methods. Given the limited range of some of them, an aircraft necessarily needs to use several of them during a flight. A handover is triggered as soon as an aircraft connects to a new ground station, which in some cases requires a change in routing to the aircraft. We propose to combine and adapt two mobility protocols, PMIPv6 and LISP, to guarantee continuity of critical data transmission while minimizing the impact on the avionics architecture and the radio communication channel. Our solution is compared to a standard IP mobility solution in a simulated network environment and specifically developed under OMNeT++. The results show that our approach reduces the handover delay, while lightening the signaling traffic on the radio channel. Moreover, in order to propose the best aircraft connectivity, we propose an automation of the selection of the best links in the multilink and ATN/IPS context. Typically, multilink algorithms (or link selection) are split into three parts : collecting link information, deciding which links to use, and using the new links. As the mobility solution proposed in this thesis is also compatible with multilink, we are interested in the first two steps. We propose to use an active method to probe the links and estimate their quality. This approach has the advantage of being independent of the underlying communication technologies. We then compare three estimation methods based on round trip delay and evaluate the performance of each of them. The first method is based on threshold determination, the second is based on a probabilistic model and the third uses supervised learning. This learning-based method makes it possible to estimate the link over time with good precision. Finally, we propose a link selection algorithm in the case where the primary link no longer meets the quality of service requirements.

Networking / Aeronautical communication systems

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Journal Paper

Hypersphere Fitting from Noisy Data Using an EM Algorithm

Authors: Lesouple Julien, Pilastre Barbara, Altmann Yoann and Tourneret Jean-Yves

IEEE Signal Processing Letters, vol. 28, pp. 314-318, January, 2021.

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This letter studies a new expectation maximization (EM) algorithm to solve the problem of circle, sphere and more generally hypersphere fitting. This algorithm relies on the introduction of random latent vectors having a priori independent von Mises-Fisher distributions defined on the hypersphere. This statistical model leads to a complete data likelihood whose expected value, conditioned on the observed data, has a Von Mises-Fisher distribution. As a result, the inference problem can be solved with a simple EM algorithm. The performance of the resulting hypersphere fitting algorithm is evaluated for circle and sphere fitting.

Signal and image processing / Earth observation

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GNSS Data Demodulation over Fading Environments: Antipodal and M-ary CSK Modulations

Authors: Ortega Espluga Lorenzo, Vilà-Valls Jordi, Poulliat Charly and Closas Pau

IET Radar, Sonar & Navigation, January, 2021.

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This article investigates new strategies to compute accurate low-complexity Log Likelihood Ratio (LLR) values based on the Bayesian formulation under uncorrelated fading channels for both antipodal and CSK modulations when no Channel State Information (CSI) is available at the receiver. These LLR values are then used as input to modern error correcting schemes used in the data decoding process of last generation GNSS signals. Theoretical analysis based on the maximum achievable rate is presented for the different methods in order to evaluate the performance degradation with respect to the optimal CSI channel. Finally, Frame Error Rate (FER) simulation results are shown, validating the appropriate performance of the proposed LLR approximation methods.

Digital communications / Localization and navigation and Space communication systems

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PhD Defense Slides

Onboard IP router for critical aeronautical communications in a heterogeneous environment

Author: Tran N'Guyen Hoang Alexandre

Defended on January 20, 2021.

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Critical aeronautical communications are a major issue for flight safety. For a long time, these have relied solely on voice, which is transmitted via an analog communication system. Given the growth in air traffic, this mean of communication has reached saturation and moreover, it has sometimes shown its limits in terms of understanding voice messages, hence the need to find an alternative method. The development of communication technologies based on digital signals allows text messages to be exchanged over a long distance. Initially reserved for noncritical airline operations, it was quickly adopted for communications between the pilot and the air traffic controller, in order to offload the dedicated radio channel. This is known as Data Link. This system, included in a more global infrastructure called the ATN/OSI, has the double advantage of relieving congestion on the frequencies used, but also of limiting the misunderstanding of certain messages. The next evolutions of this aeronautical communication system based on the IP suite and called ATN/IPS is under development. It will have to solve certain problems by proposing new communication technologies and innovative network solutions that can adapt to the increase in critical air data traffic. In this thesis, we address several issues related to the development of ATN/IPS. The first one concerns the network mobility of the aircraft. Indeed, the ATN/IPS will gather several operators, each providing their own subnetworks composed of one or more access methods. Given the limited range of some of them, an aircraft necessarily needs to use several of them during a flight. A handover is triggered as soon as an aircraft connects to a new ground station, which in some cases requires a change in routing to the aircraft. We propose to combine and adapt two mobility protocols, PMIPv6 and LISP, to guarantee continuity of critical data transmission while minimizing the impact on the avionics architecture and the radio communication channel. Our solution is compared to a standard IP mobility solution in a simulated network environment and specifically developed under OMNeT++. The results show that our approach reduces the handover delay, while lightening the signaling traffic on the radio channel. Moreover, in order to propose the best aircraft connectivity, we propose an automation of the selection of the best links in the multilink and ATN/IPS context. Typically, multilink algorithms (or link selection) are split into three parts : collecting link information, deciding which links to use, and using the new links. As the mobility solution proposed in this thesis is also compatible with multilink, we are interested in the first two steps. We propose to use an active method to probe the links and estimate their quality. This approach has the advantage of being independent of the underlying communication technologies. We then compare three estimation methods based on round trip delay and evaluate the performance of each of them. The first method is based on threshold determination, the second is based on a probabilistic model and the third uses supervised learning. This learning-based method makes it possible to estimate the link over time with good precision. Finally, we propose a link selection algorithm in the case where the primary link no longer meets the quality of service requirements.

Networking / Aeronautical communication systems

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Patent

Codage LDPC à Protection Différenciée

Authors: Ortega Espluga Lorenzo, Poulliat Charly, Al Bitar Hanaa, Boucheret Marie-Laure and Aubault-Roudier Marion

n° FR3097388, BOPI 2020-51, December 18, 2020.

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The invention provides a new method of unequal error protection which is based on a particular parity matrix structure for LDPC-type codes - Figure 1.

Digital communications / Space communication systems

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Conference Paper

Robust Tracking under Measurement Model Mismatch via Linearly Constrained Extended Kalman Filtering

Authors: Ortega Espluga Lorenzo, Vilà-Valls Jordi, Chaumette Eric, Pages Gaël and Vincent François

In Proc. 59th IEEE Conference on Decision and Control (CDC), Jeju Island, Republic of Korea, December 14-18, 2020.

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Standard state estimation techniques, ranging from the linear Kalman filter to nonlinear sigma-point or particle filters, assume a perfectly known system model, that is, process and measurement functions and system noise statistics (both the distribution and its parameters). This is a strong assumption which may not hold in practice, reason why several approaches have been proposed for robust filtering. In the context of linear filtering, a solution to cope with a possible system matrices mismatch is to use linear constraints. In this contribution we further explore the extension and use of recent results on linearly constrained Kalman filtering (LCKF) for robust tracking/localization under measurement model mismatch. We first derive the natural extension of the LCKF to nonlinear systems, and its use to mitigate parametric modelling errors in the nonlinear measurement function. A tracking problem where a set of sensors at possibly mismatched (unknown to a certain extent) positions track a moving object from time of arrival measurements is used to support the discussion.

Signal and image processing / Localization and navigation and Space communication systems

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A Compact CRB for the Single Source Conditional Signal Model with Application to Delay-Doppler-Phase Estimation of Band-Limited Signals

Authors: Ortega Espluga Lorenzo, Medina Daniel, Vilà-Valls Jordi, Vincent François and Chaumette Eric

In Proc. 59th IEEE Conference on Decision and Control (CDC), Jeju Island, Republic of Korea, December 14-18, 2020.

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The derivation of tight estimation lower bounds is a key player to design and assess the performance of new estimators. In this contribution, we derive a new compact Cramér-Rao bound (CRB) for the conditional signal model, where the deterministic parameter's vector includes a real positive amplitude and the signal phase. Then, such CRB is particularized to the delay, Doppler, phase and amplitude estimation with band-limited (narrowband) signals, where transmitter and receiver are in relative uniform radial movement. The latter expression is especially easy to use because it only depends on the signal samples. We provide illustrative results for a representative Global Navigation Satellite System positioning example.

Signal and image processing / Localization and navigation and Space communication systems

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Reactivity Enhancement of Cooperative Congestion Control for Satellite Networks

Authors: Thibaud Adrien, Fasson Julien, Arnal Fabrice, Sallantin Renaud, Dubois Emmanuel and Chaput Emmanuel

In Proc. Hot Information-Centric Networking (HotICN), Hefei, Anhui, China, December 12-14, 2020.

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The new paradigm of Information Centric Network (ICN) proposes a shift from the host-centric model to a contentcentric model. This approach, especially well suited to the current Internet’s usage, is promising for Satellite Networks. In particular, Named Data Networking (NDN) architecture seems to be a great candidate: it gathers the benefits of Content Delivery Networks (CDN), Peer-to-Peer networks (P2P) and HTTP in the network layer. In this study, we propose to compare the performances of TCP-like congestion control algorithms and our new Cooperative Congestion Control (CCC) approach. CCC is a pace-based multipath and multi-flow aware congestion control. We evaluate those algorithms with simulations on a topology where we place the satellite link on different positions. We show that CCC outperforms window-based algorithms but has still some drawbacks. We thus proposed an enhancement of CCC that corrects the flaws by increasing its reactivity. Simulations results show that the performances on terrestrial scenarios are also enhanced.

Networking / Other

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Journal Paper

Joint Delay-Doppler Estimation Performance in a Dual Source Context

Authors: Lubeigt Corentin, Ortega Espluga Lorenzo, Vilà-Valls Jordi, Lestarquit Laurent and Chaumette Eric

Remote sensing, vol. 12, issue 3, p. 3894, November, 2020.

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Evaluating the time-delay, Doppler effect and carrier phase of a received signal is a challenging estimation problem that was addressed in a large variety of remote sensing applications. This problem becomes more difficult and less understood when the signal is reflected off one or multiple surfaces and interferes with itself at the receiver stage. This phenomenon might deteriorate the overall system performance, as for the multipath effect in Global Navigation Satellite Systems (GNSS), and mitigation strategies must be accounted for. In other applications such as GNSS reflectometry (GNSS-R) it may be interesting to estimate the parameters of the reflected signal to deduce the geometry and the surface characteristics. In either case, a better understanding of this estimation problem is directly brought by the corresponding lower performance bounds. In the high signal-to-noise ratio regime of the Gaussian conditional signal model, the Cramér-Rao bound (CRB) provides an accurate lower bound in the mean square error sense. In this article, we derive a new compact CRB expression for the joint time-delay and Doppler estimation in a dual source context, considering a band-limited signal and its specular reflection. These compact CRBs are expressed in terms of the baseband signal samples, making them especially easy to use whatever the baseband signal considered, therefore being valid for a variety of remote sensors. This extends existing results in the single source context and opens the door to a plethora of usages to be discussed in the article. The proposed CRB expressions are validated in two representative navigation and radar examples.

Signal and image processing / Localization and navigation

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Activity Report

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Apply for a PhD in Safran

Codirection by Toulouse INP & ISAE-Supaero

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PhD positions available at TeSA

PhD subjects available on the CNES site.
On line application before the 2nd of April.

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EUSIPCO 2020

Conference talk of Julien Lesouple at EUSIPCO 2020

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