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Article de conférence

On the Trade-off Between Spectrum Efficiency with Dedicated Access and Short End-to-End Transmission Delays with Random Access in DVB-RCS2

Auteurs : Kuhn Nicolas, Bui Huyen-Chi, Lacan Jérôme, Radzik José et Lochin Emmanuel

In Proc. ACM LCDNet, Miami, United States, September 30, 2013.

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This paper analyses the performance of TCP over random and dedicated access methods in the context of DVB-RCS2. Random access methods introduce a lower connection delay compared to dedicated methods. We investigate the potential to improve the performance of short flows in regards to transmission delay, over random access methods for DVB-RCS2 that is currently under development. Our simulation experiments show that the transmission of the first ten IP datagrams of each TCP flow can be 500 ms faster with random access than with dedicated access making the former of interest to carry Internet traffic. Such methods, however, are less efficient in regards to bandwidth usage than dedicated access mecanisms and less reliable in overloaded network conditions. Two aspects of channel usage optimization can be distinguished: reducing the duration of ressource utilization with random access methods, or increasing the spectrum efficiency with dedicated access methods. This article argues that service providers may let low-cost users exploit the DVB-RCS2 to browse the web by introducing different services, which choice is based on the channel access method.

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Réseaux / Systèmes spatiaux de communication

Présentation de soutenance de thèse

Téléchargement de contenus dans les réseaux véhiculaires

Auteur :

Defended in September 2013

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for Intelligent Transportation Systems (ITS). They may or may not use the infrastructure. They will consider from the traffic safety applications up to the driver’s comfort or network games. The map updates are, from our point of view, a representative application but in the other hand it can help to reduce congestion in improving efficiency in decision making. It has well-defined characteristics : high volume of data, low delay constraint, possibility of implementation of infrastructure-to-vehicle communications, between vehicles and hybrids. The objective is that the contents are fully downloaded by all vehicles in minimum time, using fewer resources and lower costs. The solutions that have emerged as the most suitable concerned the use of the technology 802.11p with or without infrastructure. In the case of solutions with infrastructure, a number of access points broadcast information with coverage areas most often disjointed. Given the size of area used and/or flow devoted to this type of applications, the transition to a single access point is not enough to download these maps. It is then to define strategies of information dissemination. A first study was to compare a unicast strategy face to broadcast/multicast strategy. The latter appears largely improved. A combination of these principles does not improve system performance, because the flow devoted to unicast transmission does not compensate for the flow not used by the broadcast. The problem is duplicate chunks received by vehicles passing from several consecutive access points. To mitigate the phenomenon of duplication, we used the linear network coding pseudorandom. The idea is that the access point broadcasts linear combinations of chunks of files. The large number of these linear combinations significantly reduces this phenomenon. In a complementary manner, we investigated the use of ad hoc communications to fill the missing chunks of file, particularly in the absence of infrastructure. We verified that we could achieve good results in this context based on the diversity of chunks of files which are owned by the encountered vehicles.

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Réseaux / Localisation et navigation

Thèse de Doctorat

Téléchargement de contenus dans les réseaux véhiculaires

Auteur : Astudillo Salinas Darwin Fabian

Defended in September 2013

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The evolution of wireless communications systems have enabled to consider many applications for Intelligent Transportation Systems (ITS). They may or may not use the infrastructure. They will consider from the traffic safety applications up to the driver’s comfort or network games. The map updates are, from our point of view, a representative application but in the other hand it can help to reduce congestion in improving efficiency in decision making. It has well-defined characteristics : high volume of data, low delay constraint, possibility of implementation of infrastructure-to-vehicle communications, between vehicles and hybrids. The objective is that the contents are fully downloaded by all vehicles in minimum time, using fewer resources and lower costs. The solutions that have emerged as the most suitable concerned the use of the technology 802.11p with or without infrastructure. In the case of solutions with infrastructure, a number of access points broadcast information with coverage areas most often disjointed. Given the size of area used and/or flow devoted to this type of applications, the transition to a single access point is not enough to download these maps. It is then to define strategies of information dissemination. A first study was to compare a unicast strategy face to broadcast/multicast strategy. The latter appears largely improved. A combination of these principles does not improve system performance, because the flow devoted to unicast transmission does not compensate for the flow not used by the broadcast. The problem is duplicate chunks received by vehicles passing from several consecutive access points. To mitigate the phenomenon of duplication, we used the linear network coding pseudorandom. The idea is that the access point broadcasts linear combinations of chunks of files. The large number of these linear combinations significantly reduces this phenomenon. In a complementary manner, we investigated the use of ad hoc communications to fill the missing chunks of file, particularly in the absence of infrastructure. We verified that we could achieve good results in this context based on the diversity of chunks of files which are owned by the encountered vehicles.

Lire la suite

Réseaux / Localisation et navigation

Présentation de soutenance de thèse

Téléchargement de contenus dans les réseaux véhiculaires

Auteur : Astudillo Salinas Darwin Fabian

Defended in September 2013

Télécharger le document

The evolution of wireless communications systems have enabled to consider many applications for Intelligent Transportation Systems (ITS). They may or may not use the infrastructure. They will consider from the traffic safety applications up to the driver’s comfort or network games. The map updates are, from our point of view, a representative application but in the other hand it can help to reduce congestion in improving efficiency in decision making. It has well-defined characteristics : high volume of data, low delay constraint, possibility of implementation of infrastructure-to-vehicle communications, between vehicles and hybrids. The objective is that the contents are fully downloaded by all vehicles in minimum time, using fewer resources and lower costs. The solutions that have emerged as the most suitable concerned the use of the technology 802.11p with or without infrastructure. In the case of solutions with infrastructure, a number of access points broadcast information with coverage areas most often disjointed. Given the size of area used and/or flow devoted to this type of applications, the transition to a single access point is not enough to download these maps. It is then to define strategies of information dissemination. A first study was to compare a unicast strategy face to broadcast/multicast strategy. The latter appears largely improved. A combination of these principles does not improve system performance, because the flow devoted to unicast transmission does not compensate for the flow not used by the broadcast. The problem is duplicate chunks received by vehicles passing from several consecutive access points. To mitigate the phenomenon of duplication, we used the linear network coding pseudorandom. The idea is that the access point broadcasts linear combinations of chunks of files. The large number of these linear combinations significantly reduces this phenomenon. In a complementary manner, we investigated the use of ad hoc communications to fill the missing chunks of file, particularly in the absence of infrastructure. We verified that we could achieve good results in this context based on the diversity of chunks of files which are owned by the encountered vehicles.

Lire la suite

Réseaux / Localisation et navigation

Article de conférence

An Innovative and Efficient Frequency Estimation Method for GNSS Signals Acquisition

Auteur : Esteves Paulo

In Proc. 26th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS 2013), Nashville, TN, USA, September 16-20, 2013 (Best Student Paper Award).

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Traitement du signal et des images / Localisation et navigation

Ship Localization Using AIS Signals Received by Satellites

Auteurs : Prévost Raoul, Coulon Martial, Paimblanc Philippe, Le Maitre Julia, Millerioux Jean-Pierre et Tourneret Jean-Yves

In Proc. European Signal and Image Processing Conference (EUSIPCO), Marrakech, Morocco, September 9-13, 2013.

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This paper addresses the problem of ship localization by using the messages received by satellites and transmitted by the automatic identification system (AIS). In particular, one considers the localization of ships that do not transmit their actual position in AIS signals. The proposed localization method is based on the least squares algorithm and uses the differences of times of arrival and the carrier frequencies of the messages received by satellite. A modification of this algorithm is proposed to take into account the displacement model of the ships as additional measurements. This modification shows a significant localization improvement.

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Traitement du signal et des images / Localisation et navigation et Systèmes spatiaux de communication

Cramér-Rao Bounds and Estimation Algorithms for Delay/Doppler and Conventional Altimetry

Auteurs : Tourneret Jean-Yves, Mailhes Corinne et Halimi Abderrahim

in Proc. European Signal and Image Processing Conference (EUSIPCO), Marrakech, Morocco, September 9-13, 2013.

Delay/Doppler radar altimetry has been receiving an increasing interest, especially since the launch of the first altimeter in 2010 . It aims at reducing the measurement noise and increasing the along-track resolution in comparison with conventional pulse limited altimetry. A semi-analytical model was recently introduced for this new generation of delay/Doppler altimeters. The first contribution of this paper is the derivation of the Cram´er-Rao bounds (CRBs) associated with the parameters of this recent delay/Doppler model. These bounds are then compared with those obtained for conventional altimetry. The second contribution of this paper is the derivation of a new weighted least squares estimator based on the semianalytical delay/Doppler model. The performance of this estimator is very promising when compared to other more classical estimators and to the corresponding CRBs.

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Traitement du signal et des images / Observation de la Terre

Frequency Estimation Based on Hankel Matrices and the Alternating Direction Method of Multipliers

Auteurs : Andersson Frederik, Carlsson Marcus, Tourneret Jean-Yves et Wendt Herwig

In Proc. European Signal Processing Conference (EUSIPCO), Marrakech, Maroc, September 9-13, 2013.

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We develop a parametric high-resolution method for the estimation of the frequency nodes of linear combinations of complex exponentials with exponential damping. We use Kronecker’s theorem to formulate the associated nonlinear least squares problem as an optimization problem in the space of vectors generating Hankel matrices of fixed rank. Approximate solutions to this problem are obtained by using the alternating direction method of multipliers. Finally, we extract the frequency estimates from the con-eigenvectors of the solution Hankel matrix. The resulting algorithm is simple, easy to implement and can be applied to data with equally spaced samples with approximation weights, which for instance allows cases of missing data samples. By means of numerical simulations, we analyze and illustrate the excellent performance of the method, attaining the Cramér-Rao bound.

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Traitement du signal et des images / Systèmes de communication aéronautiques et Systèmes spatiaux de communication

Allocation de ressources pour la localisation non-cohérente par radar MIMO

Auteurs : Garcia Nil, Coulon Martial, Lops Marco et Haimovich Alexander M.

In Proc. Groupement de Recherche en Traitement du Signal et des Images (GRETSI), September 3-6, 2013.

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On considère un réseau de radars MIMO dont on cherche à déterminer la meilleure répartition de largeurs de bande et de puissance entre les différentes antennes émettrices en vue d’obtenir une certaine précision de la localisation d’une cible unique. Plus précisément, on s’intéresse ici à l’allocation optimale de bande seule, ainsi qu’à l’allocation optimale conjointement de bande et de puissance. Cette allocation s’effectue par la minimisation de la borne de Cramér-Rao. Le problème d’optimisation non-convexe obtenu est résolu par un algorithme de programmation par différence de fonctions convexes. Les résultats numériques montrent que l’allocation conjointe fournit les meilleures performances, et que d’autre part l’allocation de bande joue un rôle prépondérant dans ces performances. De plus, une borne inférieure sur la borne de Cramér-Rao optimale théorique, difficilement calculable, a également été définie, qui montre la qualité de la solution quasi-optimale.

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Traitement du signal et des images / Systèmes de communication aéronautiques

Poursuite de phase durant la démodulation et le décodage des signaux AIS reçus par satellite

Auteurs : Prévost Raoul, Coulon Martial, Bonacci David, Le Maitre Julia, Millerioux Jean-Pierre et Tourneret Jean-Yves

In Proc. Groupement de Recherche en Traitement du Signal et des Images (GRETSI), September 3-6, 2013.

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This paper presents a demodulation algorithm for automatic identification system (AIS) signals received by a satellite. The main contribution of this work is to consider the phase recovery problem for an unknown modulation index, coupled with a time-varying phase shift. The proposed method is based on a demodulator introduced in a previous paper based on a Viterbi-type algorithm applied to an extended trellis. The states of this extended trellis are composed of a trellis-code state and of a cyclic redundancy check state. The bit stuffing mechanism is taken into account by defining specific conditional transitions in the extended trellis. This algorithm estimates and tracks the phase shift by modifying the Euclidean distance used in the trellis. Simulation results obtained with and without phase tracking are presented and compared in the context of the AIS system.

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Communications numériques / Localisation et navigation et Systèmes spatiaux de communication

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