UM-CRT model optimisation

International audienceMany research on VANETs present new propagation models. This paper focus on the last optimisation of the UM-CRT model proposed by the XLIM-SIC Laboratory. The model is simplified in order to obtain a faster computation time without reducing the realism of the UM-CRT model and new criteria computed from the impulse response are also shown

Realistic wireless communication simulations for VANETS

International audienceVehicular Ad­hoc NETworks (VANETs) are mainly evaluated through simulations in which the choice of a realistic wireless channel model is a central point. Deterministic channel models bring good realism but need huge simulation time, whereas with statistical models the computational effort is reduced, but sadly so is the realism of the model. In this paper, we present a semi­deterministic channel model, called UM­CRT, based on a deterministic channel simulator, CRT (Communication Ray Tracer) and a statistical channel model, SCME-UM (Spatial Channel Model Extended - Urban Microcell). To integrate it into the NS­2 network simulator, we couple it to self­developed fully compliant 802.11p and 802.11n physical layers. Simulations in urban environment show both a good realism and a reduced computation time indicating that UM­CRT is adapted for VANETs simulations

UM-CRT : Un modèle de canal semi-déterministe pour les VANETs

National audienceLe choix d'un modèle de canal efficace pour la simulation des VANETs (Vehicular Ad-hoc NETworks) est difficile. Avec un modèle de canal purement déterministe les simulations sont réalistes mais prennent un temps très long, voire prohibitif. Dans le cas d'un modèle purement statistique, les simulations sont rapides mais le réalisme obtenu est limité. Dans ce papier nous proposons UM-CRT, un modèle de canal semi- déterministe basé sur un simulateur 3D déterministe de canal et sur le modèle statistique géométrique de canal SCME-UM (Spatial Channel Model Extended - Urban Micro). Nous avons intégré ce modèle dans le simulateur de réseaux NS-2 et montré qu'il fournit des résultats proches de ceux du modèle déterministe en un temps très nettement réduit

Utilisation du taux d'erreur binaire pour améliorer la qualité de service dans les réseaux ad hoc

Dans les réseaux sans fil ad hoc, les liens de communication sont sujets à un taux d'erreurimportant. Dans ce contexte, le routage joue un rôle stratégique pour augmenter les performancesdans les transmissions. Dans nos études, par une approche cross-layer, nous prenons en compte lafiabilité des liens dans le choix des routes. Pour cela, dans un premier temps, nous construisonsdeux nouvelles métriques, l'une basée sur le taux d'erreur binaire (au niveau couche physique) etl'autre, plus adaptée à la mesure, sur le nombre de retransmissions (au niveau couche MAC).Ensuite, pour exploiter ces métriques lors du calcul de routes, nous adaptons les algorithmes à labase des protocoles de routage.Les trois familles de protocoles de routage ont été traitées : les protocoles pro-actifs où chaquenoeud a une vision globale du réseau grâce aux échanges périodiques de messages de contrôle detopologie ; les protocoles réactifs où, avant de commencer ses transmissions de données, chaquenoeud doit initier un processus de recherche de route ; les protocoles hybrides qui mixent les deuxapproches.Pour tester l'effectivité de nos améliorations, nous utilisons le simulateur NS2 enrichi par unmodèle de propagation et un modèle de mobilité réalistes. Les paramètres de performance tels quele délai, le taux de livraison de paquets et la charge de routage sont mesurés dans plusieursscénarios représentatifs des conditions d'utilisation. Les résultats obtenus montrent une améliorationsignificative des protocoles standards dans un contexte de qualité de service.In ad hoc wireless networks, links are error-prone. In this context, routing plays a decisive role inimproving transmission performances. In our studies, by a cross-layer approach, we take intoaccount the reliability of links in route choice. For this, first, we concept two new metrics, onebased on bit error rate (at physical layer) and the other, more suitable for the measurement, onnumber of retransmissions (at MAC layer). Then, to exploit these metrics when determining routes,we adapt the algorithms based routing protocols.The three families of routing protocols have been addressed: proactive protocols where eachnode has a global view of the network through periodic exchanges of topology control messages;reactive protocols where, before starting data transmission, each node must initiate a routediscovery process; hybrid protocols which mix the two approaches.To test the effectiveness of our enhancements, we use the simulator NS.2 enhanced by arealistic propagation model and a realistic mobility model. Performance parameters such as delay,packets delivery ratio and routing load are measured in several scenarios including mobility andmulti-communication. The results show a significant improvement of standard protocols in thequality of service context.POITIERS-SCD-Bib. électronique (861949901) / SudocSudocFranceF

Stratégie d'adaptation de liens sur canaux radios dynamiques pour les communications entre véhicules (Optimisation de la qualité de service)

Cette thèse traite de l'optimisation des communications dans les réseaux véhiculaires à l'aide d'une plate-forme de simulation réaliste. Un environnement réaliste implique des modèles de mobilité adaptés aux véhicules ainsi que des modèles de couche physique détaillés (modèles decanaux et chaîne de transmission numérique). Notre travail a d'abord consisté à concevoir une plate-forme de simulation réaliste dédiée aux VANETs (Vehicular Ad hoc NETworks). Cette plate-forme a été complétée par un modèle de propagation semi-déterministe que nous avons conçu. L'avantage de ce modèle, appelé UMCRT, est d'avoir un réalisme équivalent à un modèle déterministe tout en réduisant significativement le temps de calcul. Ce modèle a été validé par comparaison avec unsimulateur déterministe à tracé de rayons.Nous avons ensuite utilisé cette plate-forme pour évaluer des protocoles de routage.L'efficacité de ces différents protocoles ad hoc testés en conditions réalistes nous a permis defocaliser notre étude sur les protocoles réactifs. De cette évaluation, nous avons retenu AODV (Ad hoc On demand Distance Vector) auquel nous avons notamment appliqué une métrique cross layer pour pallier la baisse de performance induite par le réalisme. Nous avons ensuite utilisé une technique de tuning appliquée à des protocoles réactifs. Finalement, nous avons évalué différentes couches physiques, SISO (Simple Input Simple Output) et MIMO (Multiple Imput Multiple Output). Ces travaux montrent que seules des améliorations combinées à différents niveaux (physique et réseau) permettraient d'apporter une amélioration significative des performances.This thesis deals with the optimization of communications in vehicular networks by using arealistic simulation platform. A realistic environment implies the usage of mobility modelsadapted to vehicles and also highly detailed physical models (channel models and digital transmission chain). The first part of our work has consisted in the design of a realistic simulation platformdedicated to VANETs (Vehicular Ad hoc NETworks). This platform has been completed by a semi-deterministic propagation model which we have designed. This model called UM-CRThas the advantage to have the same level of realism than a deterministic model while requiringmuch less computation time. This model has been validated by comparison with a deterministicray tracing simulator. We then have used this platform to evaluate routing protocols. The efficiency of different adhoc routing protocols in realistic conditions has led us to focus our study on the family of reactive protocols. From this evaluation we have selected AODV (Ad hoc On demand Distance Vector) to which we have applied a cross-layer metric in order to reduce the performance degradation caused by the realistic environment. We then have used a tuning technique with reactive protocols. Finally, we have evaluated several SISO and MIMO physical layers. This work shows that only improvements combined at different levels (physicaland network) can yield a significant increase in performance.POITIERS-SCD-Bib. électronique (861949901) / SudocSudocFranceF

A semi-deterministic channel model for VANETs simulations

International audienceIn this paper we propose a semi-deterministic channel propagation model for VANETs (Vehicular Ad-hoc NETworks) called UM-CRT. It is based on CRT (Communication Ray Tracer) and SCME-UM (Spatial Channel Model Extended - Urban Micro) which are respectively a deterministic channel simulator and a statistical channel model. It uses a process which adjusts the SCME-UM model using relevant parameters extracted from CRT. In order to evaluate this new model, we incorporate it into the NS-2 network simulator. Our results show that UM-CRT is adapted to VANETs simulations as it approximates in a realistic manner channel propagation mechanisms while improving simulation time

A survey of V2V channel modeling for VANET simulations

International audienceMost Vehicle to Vehicle (V2V) network protocols are evaluated by simulation. However in most network simulators, the physical layer suffers from a lack of realism. Therefore, realistic V2V channel modeling has become a crucial issue in Intelligent Transportation Systems (ITS) networks. V2V channels are known to exhibit specific features which imply the design of new simulation models. In this survey paper, we first recall the main physical features of such wireless time and frequency dispersive channels. Next, three "simulation-ready" V2V channel models found in the literature are reviewed. Finally, two complete VANET simulation frameworks are presented. They illustrate the importance of a realistic channel and physical layer modeling in vehicular networking

Taking Binary Error Rate into Account to Improve OLSR Protocol

International audienceThis paper presents BER-OLSR, an enhanced OLSR protocol. We modify OLSR standard route choice and Multi-Point Relays (MPR) selection processes. Particularly, our new protocol takes into account Bit Error Rate (BER) of links during MPR selection and routing table calculation. MPR set of a node is populated so that access to each 2-hop-neighbor is ensured by the best path in terms of BER. For routing table calculation, lowest BER is privileged over lowest number of hops. Performances of this protocol are evaluated by simulation with realistic propagation and mobility models. We show that this new approach of OLSR routing protocol provides better packet delivery ratio and delay than the original OLSR algorithm, even in unfavorable conditions such as mobility or several interfering communications

Improving ZRP performance by taking into account quality of links

International audienceMANET are characterized by their limited bandwidth and high packet error rate. In mobility, multi-path and shared bandwidth contexts, routing protocols play a major role. On-demand routing approaches lead to high delay while, in linkstate protocols, controls messages broadcasting consumes much bandwidth. Hybrid protocols such as Zone Routing Protocol (ZRP) attempt to exploit the advantages of both approaches. It uses limited scope proactive approach to maintain routes towards a surrounding zone and reactive approach to communicate with farther destinations. For a better exploitation of network capabilities, we propose a Binary Error Rate (BER) based approach of ZRP (BER-ZRP). With BER-ZRP, all phases of linkstate recording and routing tables calculation are under Quality of Service control so that better paths in terms of BER are preferred. The overhead induced by route maintenance and route discovery processes is better managed. This approach allows to improve ZRP Packet Delivery Ratio and Normalized Oversize Load

A New BER-based Approach to improve OLSR

International audienceThis paper presents a method to enhance OLSR quality of service. Our approach heavily relies on the binary error rate metric and allows to rise the packet delivery ratio (PDR). We find that two elements of OLSR must be changed, the MPR selection algorithm and the route computation. We show that our approach provides better PDR than the original OLSR algorithm