Ordonnancement et gestion des ressources pour un système de télécommunications haut débit : Optimisation de la bande passante satellite

Les télécommunications par satellite ont connu ces dernières années un regain d'intérêt important, du fait de leur capacité à permettre la réduction de la fracture numérique. En effet, un satellite en orbite géostationnaire peut s'appuyer sur une très grande couverture et une capacité importante pour atteindre des zones où le déploiement des réseaux terrestres n'est pas envisageable, comme les transports (bateau, avion), ou bien les zones blanches, où il serait difficilement rentable. Traditionnellement concentrés sur la diffusion de télévision numérique, les dernières générations de standards reflètent cet engouement en faisant une place de choix à la transmission de données bidirectionnelle, notamment en permettant une prise en charge simple des protocoles de l'Internet. Le problème de l'ordonnancement dans ces systèmes devient alors particulièrement important, puisqu'il doit prendre en compte deux processus évoluant de manière totalement décorrélée. D'un côté, l'évolution de la demande des utilisateurs, dépendante des applications (vidéo, voix, données). De l'autre, l'évolution de la capacité du système, celle-ci étant tributaire des conditions de transmission : les fréquences utilisées dans ces systèmes sont particulièrement sensibles à l'atténuation due à l'eau dans l'atmosphère. Cette thèse s'intéresse au problème de l'ordonnancement et de l'allocation de ressources, dans le but de fournir un service comparable aux réseaux terrestres en termes de services, en présentant les meilleures performances possibles. Si un certain nombre de propositions ont été faites sur le sujet, aucune ne prend en compte l'ensemble des contraintes d'un tel système. Outre le caractère variable de la capacité, la variabilité de la demande, conjuguée avec les contraintes de qualité de service constitue une difficulté supplémentaire. Enfin, il nous faut considérer la faisabilité de notre solution dans un contexte temps réel, nécessaire dans l'optique d'une implantation dans un système réel. Nous avons ainsi développé une architecture d'ordonnanceur pour la voie Aller, reposant sur des fonctions d'utilité, permettant ainsi une formulation simple du compromis entre demande et capacité. Nous montrons comment cet algorithme pourrait être utilisable dans un système complet, à travers une implantation détaillée, de faible complexité, ainsi que des simulations de cas réels. Nous portons ensuite notre attention sur la voie Retour, où nous proposons une méthode d'allocation de ressources prenant en compte de manière conjointe la qualité de service et la qualité du support pour délivrer une allocation à la fois conforme et performante. Les simulations montrent que notre algorithme obtient une efficacité et une meilleure gestion du trafic que des solutions de référence présentées dans la littérature

Dynamic unsplittable flows with path-change penalties: new formulations and solution schemes for large instances

In this work, we consider the dynamic unsplittable flow problem. This variation of the unsplittable flow problem has received little attention so far. The unsplittable flow problem is an NP-hard extension of the multi-commodity flow problem where each commodity sends its flow on only one path. In its dynamic version, this problem features several time steps and a penalty is paid when a commodity changes its path from one time step to the next. We present several mixed-integer linear programming formulations for this problem and compare the strength of their linear relaxation. These formulations are embedded in several solvers which are extensively compared on small to large instances. One of these formulations must be solved through a column generation process whose pricing problem is more difficult than those used in classical flow problems. We present limitations of the pricing schemes proposed in earlier works and describe two new schemes with a better worst-case complexity. Overall, this work lays a strong algorithmic baseline for the resolution of the dynamic unsplittable flow problem, proposes original formulations, and discusses the compared advantages of each, thus hopefully contributing a step towards a better understanding of this problem for both OR researchers and practical applications

Randomized rounding algorithms for large scale unsplittable flow problems

Unsplittable flow problems cover a wide range of telecommunication and transporta- tion problems and their efficient resolution is key to a number of applications. In this work, we study algorithms that can scale up to large graphs and important num- bers of commodities. We present and analyze in detail a heuristic based on the linear relaxation of the problem and randomized rounding. We provide empirical evidence that this approach is competitive with state-of-the-art resolution methods either by its scaling performance or by the quality of its solutions. We provide a variation of the heuristic which has the same approximation factor as the state-of-the-art approxima- tion algorithm. We also derive a tighter analysis for the approximation factor of both the variation and the state-of-the-art algorithm. We introduce a new objective function for the unsplittable flow problem and discuss its differences with the classical con- gestion objective function. Finally, we discuss the gap in practical performance and theoretical guarantees between all the aforementioned algorithms

Software-defined satellite cloud RAN

This paper provides a feasibility study on the virtualization of a DVB-S2/DVB-RCS2 satellite ground infrastructure and its SDN-based management and control. The proposed framework, SatCloudRAN, is expected to increase the opportunities of smoothly integrating the satellite components in forthcoming 5G systems. We analyze the design of SatCloudRAN by considering various chaining of virtual and physical functions and the characteristics of the links between them. We based our analysis on a generic architecture of bidirectional access networks that follows the normative documents of the broadband forum and leverage virtualization and softwarization technologies, namely NFV and SDN, to achieve a flexible and programmable control and management of satellite infrastructure. Using a SatCloudRAN approach, network operators will be able to provide: (1) optimized dynamic QoS, (2) resilient management of multiple satellite gateways, and (3) dynamic bandwidth on demand. Copyright c 2016 John Wiley & Sons, Ltd

Software-defined satellite cloud RAN

This is the peer reviewed version of the following article: Ahmed, T., Dubois, E., Dupé, J.-B., Ferrús, R., Gélard, P., and Kuhn, N. (2018) Software-defined satellite cloud RAN. Int. J. Satell. Commun. Network., 36: 108–133, which has been published in final form at 10.1002/sat.1206. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.This paper provides an assessment study on the virtualization of a Digital Video Broadcasting - Satellite - Second Generation (DVB-S2)/ Digital Video Broadcasting - Return Channel Satellite - Second Generation (DVB-RCS2) satellite ground infrastructure and proposes a framework, named Satellite Cloud Radio Access Network (SatCloudRAN), that aims to ease the integration of satellite components in forthcoming 5G systems. Special attention is given to the design of SatCloudRAN by considering the split and placement of virtualized and nonvirtualized functions while taking into account the characteristics of the transport links connecting both type of functions. We assess how virtualization and softwarization technologies, namely, network function virtualization and software-defined networking, can deliver part of the satellite gateway functionalities as virtual network functions and achieve a flexible and programmable control and management of satellite infrastructure. Under the network function virtualization paradigm, building virtual network function blocks that compose a satellite gateway have been identified, and their interaction exhibited. This paper also gives insights on how the SatCloudRAN approach can allow operators to provide software-defined networking-based (1) bandwidth on demand, (2) dynamic Quality of Service, and (3) satellite gateway diversity.Peer ReviewedPreprin

On the Impact of Intrinsic Delay Variation Sources on Iridium LEO Constellation

The recent decades have seen an increasing interest in Medium Earth Orbit and Low Earth Orbit satellite constellations. However, there is little information on the delay variation characteristics of these systems and the resulting impact on high layer protocols. To fill this gap, this paper simulates a constellation that exhibits the same delay characteristics as the already deployed Iridium but considers closer bandwidths to constellation projects’. We identify five major sources of delay variation in polar satellite constellations with different occurrence rates: elevation, intra-orbital handover, inter-orbital handover, orbital seam handover and Inter-Satellite Link changes. We simulate file transfers of different sizes to assess the impact of each of these delay variations on the file transfer. We conclude that the orbital seam is the less frequent source of delay and induces a larger impact on a small file transfers: the orbital seam, which occurs at most three times during 24 h, induces a 66% increase of the time needed to transmit a small file. Inter-orbital and intra-orbital handovers occur less often and reduce the throughput by approximately ∼ 8% for both low and high throughput configurations. The other sources of delay variations have a negligible impact on small file transfers, and long file transfers are not impacted much by the delay variations

Deterministic Distribution of Replicas Positions for Multiuser Random Transmissions in Satcoms

International audienceRandom 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

Procédé et système de transmission de paquets de données à travers un canal de transmission (ra) à accès aléatoire

Un procédé de transmission de paquets de données à travers un canal de transmission (RA) à accès aléatoire, partagé par une pluralité de terminaux utilisateurs, utilise et exploite une fonction d’attribution et de distribution F de ressources de transmission F(u) aux terminaux utilisateurs dont la connaissance du graphe est partagée par les terminaux utilisateurs émetteurs et la station de réception dans une étape préalable. Lors du décodage des paquets reçus, le graphe {(u, F(u)} de la fonction d’attribution et de distribution est exploité par la station de réception pour minimiser, voire annuler, le nombre de corrélations de localisation de répliques. requises en cas de blocage du processus de décodage classique du protocole CRDSA

Asynchronous Packet Localization with Random SPOTiT in Satellite Communications.

Abstract—Recently, many different Random Access protocols have been developed and proposed for satellite return link communications. Synchronous and asynchronous solutions vary, mainly, in terms of signaling overhead regarding synchronization information. On the one hand, Contention Resolution Diversity Slotted Aloha (CRDSA) has emerged as a leader technique for synchronous transmissions with multiple replicas per packet and Successive Interference Cancellation at reception. On the other hand, Asynchronous Contention Resolution Diversity ALOHA (ACRDA) has been proposed as an equivalent asynchronous method to CRDSA. CRDSA and ACRDA incur a deadlock when no more packets can be retrieved due to high channel loads. Therefore, a complementary method to CRDSA: MultireplicA decoding using corRelation baSed locAlisation (MARSALA) proposed to combine replicas belonging to the same undecoded packet after localizing them through correlations. This allows to unlock some of the deadlock configurations which would re-launch CRDSA again. In asynchronous transmissions, Enhanced Contention Resolution Aloha (ECRA) uses different combining techniques for packets replicas to offer high system performance in terms of Packet Loss Ratio (PLR) and throughput. The former and latter techniques MARSALA and ECRA can be costly in localization complexity to the receiver. Therefore, Shared Position Technique for Interfered Random Transmissions (R-SPOTiT) defines a way to reduce the complexity of MARSALA’s packets localization without degrading performance nor adding extra signaling information. Accordingly, this paper proposes AR-SPOTiT, an asynchronous design of R-SPOTiT, as a complementary method to ACRDA that introduces a way to locate replicas on their virtual frames with less complexity and significantly higher system performance compared to ACRDA

Shared Position Technique for Interfered Random Transmissions in Satellite Communications

International audienceIn 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