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PhD Thesis

Synchronisation, détection et égalisation de modulation à phase continue dans des canaux sélectifs en temps et en fréquence

Author: Chayot Romain

Defended on January 15, 2019.

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Digital communications / Aeronautical communication systems and Space communication systems

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PhD Defense Slides

Synchronisation, détection et égalisation de modulation à phase continue dans des canaux sélectifs en temps et en fréquence

Author: Chayot Romain

Defended on January 15, 2019.

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Digital communications / Aeronautical communication systems and Space communication systems

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Journal Paper

Impact of Delayed Acknowledgments on Transport Layer Performance over Low Orbit Constellations

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

Journal of Spacecraft and Rockets, special issue, December, 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

Deterministic Distribution of Replicas Positions for Multiuser Random Transmissions in Satcoms

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

In Proc. IEEE Global Communications Conference, Abu Dhabi, UAE, December 9-13, 2018.

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Random Access (RA) protocols have considerably evolved in satellite communications, especially after the introduction of Contention Resolution Diversity Slotted Aloha (CRDSA). However, CRDSA finds itself in a deadlock when the number of users is important. A complementary treatment Multireplica Decoding using Correlation based Localization (MARSALA) has hence been proposed to unlock CRDSA. This is fulfilled by localizing then combining replicas of the same undecoded packets using correlations. Based on a prior knowledge of the potential frame content by the receiver, a random Shared POsition Technique for Interfered random Transmissions (SPOTiT) is proposed to reduce MARSALA’s localization complexity. As a matter of fact, random SPOTiT highlights a manner for the receiver to be aware of time slot positions and the preamble used by each subscriber. Then it uses this information to target a lower number of slots for localization correlations. In this paper we propose a hybrid solution that mixes both DAMA and Random Access in order to lower the Packet Loss Ratio (PLR) floor. In fact, a centralized computing can manage replicas positions and preambles to use, in a way that no loops are created. This also allows to keep a simple packet localization as in SPOTiT. Hereafter, we provide an optimal distribution of frame content using two replicas per packet which is evaluated through simulation.

Digital communications / Space communication systems

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

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

In Proc. ESA Workshop on Satellite Navigation Technologies and European Workshop on GNSS Signals and Signal Processing (NAVITEC), Noordwijk, The Netherlands, December 5-7, 2018.

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Reducing the Time To First Fix (TTFF) and improving the resilience of future Galileo signals are two important characteristics, especially when considering urban environments. To reach these goals, we studied two new advanced techniques based on the co-design of the message structure and the channel coding scheme. The first technique proposes a reduction of time needed to retrieve the data by reinforcing the parity check matrix structure constraints. The second technique provides an enhancement of the retrieved data error rate in parallel to a reduction of the time needed to retrieve the data thanks to a new co-design requirement based on a family of codes inspired from the rate-compatible root LDPC codes. The results obtained are promising, since the time to retrieve the data (and thus the TTFF) is significantly reduced, while keeping a good level of demodulation performance.

Signal and image processing and Digital communications / Localization and navigation

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PhD Thesis

ON THE INTERACTION BETWEEN TRANSPORT PROTOCOLS AND LINK-LAYER RELIABILITY SCHEMES FOR SATELLITE MOBILE SERVICES

Author: Tauran Bastien

Defended on December 12, 2018.

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Networking / Space communication systems

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PhD Defense Slides

ON THE INTERACTION BETWEEN TRANSPORT PROTOCOLS AND LINK-LAYER RELIABILITY SCHEMES FOR SATELLITE MOBILE SERVICES

Author: Tauran Bastien

Defended on December 6, 2018.

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Networking / Space communication systems

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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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PhD Thesis

Nouvelle forme d’onde et récepteur avancé pour la télémesure des futurs lanceurs

Author: Piat-Durozoi Charles-Ugo

Defended on November 27, 2018.

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Les modulations à phase continue (CPMs) sont des methodes de modulations robuste à la non-cohérence du canal de propagation. Dans un context spatial, les CPM sont utilisées dans la chaîne de transmission de télémesure de la fusée. Depuis les années 70, la modulation la plus usitée dans les systèmes de télémesures est la modulation CPFSK continuous phase frequency shift keying filtrée. Historiquement, ce type de modulation est concaténée avec un code Reed-Solomon (RS) afin d’améliorer le processus de décodage. Côté récepteur, les séquences CPM non-cohérentes sont démodulées par un détecteur Viterbi à sortie dure et un décodeur RS. Néanmoins, le gain du code RS n’est pas aussi satisfaisant que des techniques de codage moderne capables d’atteindre la limite de Shannon. Actualiser la chaîne de communication avec des codes atteignant la limite de Shannon tels que les codes en graphe creux, implique de remanier l’architecture du récepteur usuel pour un détecteur à sortie souple. Ainsi, on propose dans cette étude d’ élaborer un détecteur treillis à sortie souple pour démoduler les séquences CPM non-ohérentes. Dans un deuxième temps, on concevra des schémas de pré-codages améliorant le comportement asymptotique du récepteur non-cohérent et dans une dernière étape on élabora des codes de parité à faible densité (LDPC) approchant la limite de Shannon.

Digital communications / Space communication systems

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PhD Defense Slides

Nouvelle forme d’onde et récepteur avancé pour la télémesure des futurs lanceurs

Author: Piat-Durozoi Charles-Ugo

Defended on November 27, 2018.

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Digital communications / Space communication systems

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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).