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Conference Paper

Physical Layer Abstraction for Performance Evaluation of LEO Satellite Systems for IoT using Time-Frequency Aloha Scheme

Authors: Cluzel Sylvain, Dervin Mathieu, Radzik José, Cazalens Sonia, Baudoin Cédric and Dragomirescu Daniela

In Proc. 6th IEEE Global Conference on Signal and Information Processing (GlobalSIP), Anaheim, California, USA, November 26–29, 2018.

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One of the main issues in using a Low Earth Orbit (LEO) satellite constellation to extend a Low-Powered Wide Area Network is the frequency synchronization. Using a link based on random access solves this concern, but also prevents delivery guarantees, and implies less predictable performance. This paper concerns the estimation of Bit Error Rate (BER) and Packet Error Rate (PER) using physical layer abstractions under a time and frequency random scheme, namely Time and Frequency Aloha. We first derive a BER calculation for noncoded QPSK transmission with one collision. Then, we use the 3GPP LTE NB-IoT coding scheme. We analyze the interference that could be induced by repetition coding scheme and propose an efficient summation to improve the decoder performance. Finally, to estimate a PER for any collided scenario, we propose a physical layer abstraction, which relies on an equivalent Signal-to-Noise Ratio (SNR) calculation based on Mutual Information.

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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Journal Paper

Impact of Delayed Acknowledgment on TCP Performance over LEO Satellite Constellations

Authors: Tauran Bastien, Lochin Emmanuel, Lacan Jérôme, Arnal Fabrice, Gineste Mathieu and Kuhn Nicolas

Journal of Spacecraft and Rockets, special issue, October, 2018.

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Satellite transmissions can suffer from high channel impairments, especially on the link between a satellite and a mobile end user. To cope with these errors, physical and link layer reliability schemes have been introduced at the price of an increased end-to-end delay seen by the transport layer (e.g. TCP). By default, TCP enables Delayed Acknowledgment (DelAck), that might increase the end-to-end delay when performing over satellite link-layer recovery schemes. As a matter of fact, even if this option enables to decrease the feedback path load and the stack processing overhead, it might be counterproductive in a satellite context. This motivates the present paper that aims at quantifying the impact of such TCP option in the context of Low Earth Orbit (LEO) satellite constellations. We perform several simulation measurements with two well-deployed TCP variants and show that DelAck should be disabled when used over link-layer HARQ schemes particularly when these schemes enable reordering buffer.

Networking / Space communication systems

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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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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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Conference Paper

Controlled Delay Scheduler for VoIP over LEO constellations on LMS channels

Authors: Tauran Bastien, Lochin Emmanuel, Lacan Jérôme, Arnal Fabrice, Gineste Mathieu and Kuhn Nicolas

In Proc. 9th Advanced Satellite Multimedia Systems Conference (ASMS), Berlin, Germany, September 10-12, 2018.

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Satellite transmissions can suffer from high channel impairments, especially on the link between a satellite and a mobile end-user. To cope with these errors, physical and link layer reliability schemes have been introduced at the price of an end-to-end delay increase resulting in high jitter. Unfortunately, both the delay and the jitter negatively impacts on multimedia traffic. As a matter of fact, not taking into account the channel state greatly decreases the Quality of Experience (QoE) of VoIP users. In this paper, we propose to solve this issue by scheduling data transmission as a function of the channel condition. We first investigate existing scheduling mechanisms and analyze their performance for VoIP traffic with the objective to lower both latency and jitter, which are the most important metrics to achieve a consistent VoIP service. We select the best candidate among several schedulers and propose a novel algorithm specifically designed to carry VoIP over LEO constellations. Our simulations show that in some scenarios, we double the QoE of VoIP users.

Networking / Space communication systems

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Shared Position Technique for Interfered Random Transmissions in Satellite Communication

Authors: Zamoum Selma, Lacan Jérôme, Boucheret Marie-Laure, Dupé Jean-Baptiste and Gineste Mathieu

In Proc. 9th Advanced Satellite Multimedia Systems Conference (ASMS), Berlin, Germany, September 10-12, 2018.

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In this paper we propose a new random access (RA) channel technique for the return link of satellite communications. It concerns slotted transmissions. This proposed method called Shared POsition Technique for Interfered random Transmissions (SPOTiT), is based on a shared knowledge between the receiver and each of the terminals. The shared information is about the time slot locations on which the terminal transmits its replicas as well as the preamble to use. The presented random version of SPOTiT aims to reduce the complexity of replicas localization process of the legacy technique Multireplica Decoding using Correlation based Localisation (MARSALA). It presents a less complex system without degrading performance and with no extra signaling information. Thus, SPOTiT is applied at the same level as MARSALA, i.e. when Contention Resolution Diversity Slotted Aloha (CRDSA) fails in retrieving more packets. This technique combined with CRDSA significantly reduces the number of data localization correlations, while maintaining the same performance as in CRDSA/MARSALA in terms of packet loss ratio and throughput.

Digital communications / Space communication systems

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PhD Defense Slides

Optimisation de la gestion des ressources sur la voie retour

Author: Couble Yoann

Defended on September 3rd, 2018.

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Networking / Space communication systems

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Activity Report

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TeSA in Miami

Philippe Paimblanc, TeSA Researcher, Julien Lesouple and Lorenzo Ortega, TeSA PhD students, presented papers at ION GNSS+ 2018.

TeSA in Berlin

Bastien Tauran and Selma Zamoum, TeSA PhD students, presented papers at ASMS/SPSC 2018.

Yoann Couble becomes a Doctor

Congratulations!