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Conference Paper

Doubly-Selective Channel Estimation for Continuous Phase Modulation

Authors: Chayot Romain, Thomas Nathalie, Poulliat Charly, Boucheret Marie-Laure, Van Wambeke Nicolas and Lesthievent Guy

In Proc. 37th premier international conference for military communications (MILCOM), Los Angeles, USA, October 29-31, 2018.

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In this paper, we present two Data-Aided channel estimators for Continuous Phase Modulation (CPM) in the case of transmissions over doubly-selective channels. They both capitalize on the Basis Expansion Model (BEM), widely used for OFDM systems and for Single Carrier transmission with linear modulation. However, in the case of CPM signals, we need to work on a over-sampled received signal (fractionally-spaced representation) as the equalization techniques are also working on the over-sampled received signal. The first one is a classical Least Squares (LS) estimation of the BEM parameters whereas the second channel estimator introduces first a parametric dependence on the paths delays. Indeed, in the case where those delays are known (by estimation or by geometrical consideration as for the aeronautical channel by satellite), the second LS estimation on the BEM parameters is improved and less computationally demanding. Simulations results are provided and show good performance of our parametric LS estimation.

Digital communications / Aeronautical communication systems and Space communication systems

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Precoding for Non-coherent detection of continuous phase modulations

Authors: Piat-Durozoi Charles-Ugo, Poulliat Charly, Thomas Nathalie, Boucheret Marie-Laure, Lesthievent Guy and Bouisson Emmanuel

In Proc. 37th premier international conference for military communications (MILCOM), Los Angeles, USA, October 29-31, 2018.

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Non-coherent trellis based receiver (TBR) is an effective method to demodulate noncoherent continuous-phase modulated sequences. However it requires to increase the observation length to reach the performance of classical coherent TBRs. Furthermore it appears that both receivers offers different behaviours when considered in a bit-interleaved coded modulation (BICM) system using iterative decoding. Indeed, trellis based outer coding schemes performing well in coherent regime generate error floors in non-coherent regime. In this paper, we show that precoding of the continuous phase modulation (CPM) encoder can deal with the latter issue. The optimization of this non-coherent precoding relies on different objectives than the existing precoding methods introduced in the coherent case. The optimization relies on some asymptotic arguments enabling an efficient BICM scheme using iterative decoding. Using the proposed precoding approach enables to remove error floors in the non-coherent regime while enabling transparent use in the coherent case.

Digital communications / Space communication systems

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Cardiac Motion Estimation with Dictionary Learning and Robust Sparse Coding in Ultrasound Imaging

Authors: Ouzir Nora, Chiril Patricia, Basarab Adrian and Tourneret Jean-Yves

In Proc. EEE International Ultrasonics Symposium, Kobe, Japan, October 22-25, 2018.

Earth observation

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PhD Thesis

Advanced Signal Processing Methods for GNSS Positioning with NLOS/Multipath Signals

Author: Kbayer Nabil

Defended on October 9, 2018.

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Signal and image processing / Localization and navigation

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PhD Defense Slides

Advanced Signal Processing Methods for GNSS Positioning with NLOS/Multipath Signals

Author: Kbayer Nabil

Defended on October 9, 2018.

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Signal and image processing / Localization and navigation

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Conference Paper

Cycle Slip Detection in Galileo Widelane Signals Tracking

Authors: Paimblanc Philippe, Jardak Nabil, Bouilhac Margaux, Junique Thomas and Robert Thierry

In Proc. 31st International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS+), Miami, Florida, USA, September 24 - 28, 2018.

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Precise positioning (based on Precise Point Positioning, PPP, or Real Time Kinematics, RTK) is steadily gaining momentum. The main difficulty when using carrier phase measurements remains to correctly estimate their ambiguities: not only is it a computationally intensive process, but it can be affected by cycle slips (CS), which are brutal variations in ambiguity values, due to receiver’s dynamics or unfortunate reception events. As GNSS constellations are now able to provide users with signals on three different frequencies, the concept of Triple Carrier Ambiguity Resolution has become widespread. It typically relies on the use of widelane signals, which are combinations of raw signals and are defined as to have an apparent wavelength much higher than original signals, thus making accelerating the ambiguity fixing process and reducing the frequency of cycle slips. However, CS may remain a problem for the availability of precise positioning services. The present paper therefore focuses on a cycle slip detection method, based on a hypothesis test. The main idea consists in using both code and widelane phase measurements to compute a geometry- and ionospheric-free test vector, theoretically containing only noise and possible cycle slips. The latter can be detected by looking for brutal changes on the average of the test vector. Performance is assessed on simulated and Rinex data.

Signal and image processing / Localization and navigation

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Co-Design of Message Structure and Channel Coding Scheme to Reduce the Time to CED for a Galileo 2nd Generation New Signal

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

In Proc. Institute of Navigation (ION GNSS+), Miami, Florida, USA, September 24-28, 2018.

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In the recent times, the interest of reducing the time to retrieve the Clock and Ephemerides Data (CED) has provided an open subject of study to design the structure of the message along with the channel coding scheme of the GNSS signals. As a direct consequence, a new methodology to co-design the navigation message and the channel coding scheme structure is proposed in this paper. This new co-design enables both to reduce the time to retrieve the CED and enhanced error correction capabilities under degraded channel conditions. In order to accomplish such as requirements, codes, which provide both maximum distance separable and full diversity properties under the non-ergodic channel assumption, are designed.

Signal and image processing and Digital communications / Localization and navigation

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Robust Covariance Matrix Estimation and Sparse Bias Estimation for Multipath Mitigation

Authors: Lesouple Julien, Barbiero Franck, Faurie Frédéric, Sahmoudi Mohamed and Tourneret Jean-Yves

In Proc. ION GNSS+, Miami, Florida, USA, September 24-28, 2018.

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Multipath is an important source of error when using global navigation satellite systems (GNSS) in urban environment, leading to biased measurements and thus to false positions. This paper treats the GNSS navigation problem as the resolution of an overdetermined system, which depends on the receiver’s position, velocity, clock bias, clock drift, and possible biases affecting GNSS measurements. We investigate a sparse estimation method combined with an extended Kalman filter to solve the navigation problem and estimate the multipath biases. The proposed sparse estimation method assumes that only a part of the satellites are affected by multipath, i.e., that the unknown bias vector is sparse in the sense that several of its components are equal to zero. The natural way of enforcing sparsity is to introduce an l1 regularization ensuring that the bias vector has zero components. This leads to a least absolute shrinkage and selection operator (LASSO) problem, which is solved using a reweighted-l1 algorithm. The weighting matrix of this algorithm is defined as functions of the carrier to noise density ratios and elevations of the different satellites. Moreover, the smooth variations of multipath biases versus time are enforced using a regularization based on total variation. For estimating the noise covariance matrix, we use an iterative reweighted least squares strategy based on the so-called Danish method. The performance of the proposed method is assessed via several simulations conducted on different real datasets.

Signal and image processing / Localization and navigation

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Talk

Polar Codes: Information Theoretic Analysis and Performances

Author: Benammar Meryem

Seminar of TeSA, Toulouse, September 20, 2018.

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Digital communications / Aeronautical communication systems and Space communication systems

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Journal Paper

New CO² Concentration Predictions and Spectral Estimation Applied to the Vostok Ice Core

Authors: Bonacci David and Lacaze Bernard

IEEE Transactions on Geoscience and Remote Sensing, vol. 56, issue 1, pp. 145-151, January, 2018.

The Vostok ice core provides measurements of the CO 2 concentration during the last 414 × 10 3 years (yr). Estimations of power spectra show peaks, with the strongest one corresponding to a time period of around 100 × 10 3 yr. In this paper, a new reconstruction method from irregular sampling is used, allowing more accurate estimation of spectral peaks. This method intrinsically decomposes the analyzed signal as a sum of sines, providing amplitudes but also phase measurements of periodic tendencies (due to the nature of the studied phenomena). This decomposition can be conducted with noisy and inaccurate measurements of the sampling instants and the concentrations. The widely used Vostok data were chosen as an example, but the method could also be applied to data from other places (e.g., dome C, Antarctica) or to study other phenomena as nitrogen dioxide NO 2 , methane CH 4 , oxygen isotope 18 O (closely linked to temperature), deuterium 2 H, or dust concentrations.

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Activity Report

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PhD positions available at TeSA

PhD subjects available on the CNES site.
On line application before the 1st of April.

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Romain Chayot and Charles-Ugo Piat-Durozoi become Doctors

Congratulations!

Welcome to our new PhD students!

On this picture: Thomas, Vinicius and François (from left to right).