6 research outputs found
Enhancing infotainment applications quality of service in vehicular ad hoc networks
Les réseaux ad hoc de véhicules accueillent une multitude d’applications intéressantes. Parmi celles-ci, les applications d’info-divertissement visent à améliorer l’expérience des passagers. Ces applications ont des exigences rigides en termes de délai de livraison et de débit. De nombreuses approches ont été proposées pour assurer la qualité du service des dites applications. Elles sont réparties en deux couches : réseau et contrôle d’accès. Toutefois, ces méthodes présentent plusieurs lacunes.
Cette thèse a trois volets. Le premier aborde la question du routage dans le milieu urbain. A cet égard, un nouveau protocole, appelé SCRP, a été proposé. Il exploite l’information sur la circulation des véhicules en temps réel pour créer des épines dorsales sur les routes et les connecter aux intersections à l’aide des nœuds de pont. Ces derniers collectent des informations concernant la connectivité et le délai, utilisées pour choisir les chemins de routage ayant un délai de bout-en-bout faible. Le deuxième s’attaque au problème d’affectation des canaux de services afin d’augmenter le débit. A cet effet, un nouveau mécanisme, appelé ASSCH, a été conçu. ASSCH collecte des informations sur les canaux en temps réel et les donne à un modèle stochastique afin de prédire leurs états dans l’avenir. Les canaux les moins encombrés sont sélectionnés pour être utilisés. Le dernier volet vise à proposer un modèle analytique pour examiner la performance du mécanisme EDCA de la norme IEEE 802.11p. Ce modèle tient en compte plusieurs facteurs, dont l’opportunité de transmission, non exploitée dans IEEE 802.11p.The fact that vehicular ad hoc network accommodates two types of communications, Vehicle-to-Vehicle and Vehicle-to-Infrastructure, has opened the door for a plethora of interesting applications to thrive. Some of these applications, known as infotainment applications, focus on enhancing the passengers' experience. They have rigid requirements in terms of delivery delay and throughput. Numerous approaches have been proposed, at medium access control and routing layers, to enhance the quality of service of such applications. However, existing schemes have several shortcomings. Subsequently, the design of new and efficient approaches is vital for the proper functioning of infotainment applications.
This work proposes three schemes. The first is a novel routing protocol, labeled SCRP. It leverages real-time vehicular traffic information to create backbones over road segments and connect them at intersections using bridge nodes. These nodes are responsible for collecting connectivity and delay information, which are used to select routing paths with low end-to-end delay. The second is an altruistic service channel selection scheme, labeled ASSCH. It first collects real-time service channels information and feeds it to a stochastic model that predicts the state of these channels in the near future. The least congested channels are then selected to be used. The third is an analytical model for the performance of the IEEE 802.11p Enhanced Distributed Channel Access mechanism that considers various factors, including the transmission opportunity (TXOP), unexploited by IEEE 802.11p
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Intelligent and bandwidth-efficient medium access control protocols for IEEE 802.11p-based Vehicular Ad hoc Networks
Vehicle-to-Vehicle (V2V) technology aims to enable safer and more sophisticated transportation via the spontaneous formation of Vehicular Ad hoc Networks (VANETs). This type of wireless networks allows the exchange of kinematic and other data among vehicles, for the primary purpose of safer and more efficient driving, as well as efficient traffic management and other third-party services. Their infrastructure-less, unbounded nature allows the formation of dense networks that present a channel sharing issue, which is harder to tackle than in conventional WLANs.
This thesis focuses on optimising channel access strategies, which is important for the efficient usage of the available wireless bandwidth and the successful deployment of VANETs. To start with, the default channel access control method for V2V is evaluated hardware via modifying the appropriate wireless interface Linux driver to enable finer on-the-fly control of IEEE 802.11p access control layer parameters. More complex channel sharing scenarios are evaluated via simulations and findings on the behaviour of the access control mechanism are presented. A complete channel sharing efficiency assessment is conducted, including throughput, fairness and latency measurements. A new IEEE 802.11p-compatible Q-Learning-based access control approach that improves upon the studied protocol is presented. The stations feature algorithms that “learn” how to act optimally in VANETs in order to maximise their achieved packet delivery and minimise bandwidth wastage. The feasibility of Q-Learning to be used as the base of selflearning protocols for IEEE 802.11p-based V2V communication access control in dense environments is investigated in terms of parameter tuning, necessary time of exploration, achieving latency requirements, scaling, multi-hop and accommodation of simultaneous applications. Additionally, the novel Collection Contention Estimation (CCE) mechanism for Q-Learning-based access control is presented. By embedding it on the Q-Learning agents, faster convergence, higher throughput, better service separation and short-term fairness are achieved in simulated network deployments.
The acquired new insights on the network performance of the proposed algorithms can provide precise guidelines for efficient designs of practical, reliable, fair and ultra-low latency V2V communication systems for dense topologies. These results can potentially have an impact across a range of related areas, including various types of wireless networks and resource allocation for these, network protocol and transceiver design as well as QLearning applicability and considerations for correct use
Quality-Driven Cross-Layer Protocols for Video Streaming over Vehicular Ad-Hoc Networks
The emerging vehicular ad-hoc networks (VANETs) offer a variety of applications
and new potential markets related to safety, convenience and entertainment, however,
they suffer from a number of challenges not shared so deeply by other types of existing
networks, particularly, in terms of mobility of nodes, and end-to-end quality of service
(QoS) provision. Although several existing works in the literature have attempted to
provide efficient protocols at different layers targeted mostly for safety applications, there remain many barriers to be overcome in order to constrain the widespread use of such networks for non-safety applications, specifically, for video streaming: 1) impact of high
speed mobility of nodes on end-to-end QoS provision; 2) cross-layer protocol design while keeping low computational complexity; 3) considering customer-oriented QoS metrics in the design of protocols; and 4) maintaining seamless single-hop and multi-hop connection between the destination vehicle and the road side unit (RSU) while network is moving.
This thesis addresses each of the above limitations in design of cross-layer protocols for video streaming application. 1) An adaptive MAC retransmission limit selection scheme is proposed to improve the performance of IEEE 802.11p standard MAC protocol for video streaming applications over VANETs. A multi-objective optimization framework, which jointly minimizes the probability of playback freezes and start-up delay of the streamed video at the destination vehicle by tuning the MAC retransmission limit with respect to channel statistics as well as packet transmission rate, is applied at road side unit (RSU). Two-hop transmission is applied in zones in which the destination
vehicle is not within the transmission range of any RSU. In the multi-hop scenario, we
discuss the computation of access probability used in the MAC adaptation scheme and propose a cross-layer path selection scheme; 2) We take advantage of similarity between multi-hop urban VANETs in dense traffic conditions and mesh connected networks. First, we investigate an application-centric routing scheme for video streaming over mesh connected overlays. Next, we introduce the challenges of urban VANETs compared to mesh networks and extend the proposed scheme in mesh network into a protocol for urban VANETs. A classification-based method is proposed to select an optimal path for video streaming over multi-hop mesh networks. The novelty is to translate the path selection
over multi-hop networks to a standard classification problem. The classification is based on minimizing average video packet distortion at the receiving nodes. The classifiers are trained offline using a vast collection of video sequences and wireless channel conditions in order to yield optimal performance during real time path selection. Our method substantially reduces the complexity of conventional exhaustive optimization methods and results in high quality (low distortion). Next, we propose an application-centric routing scheme for real-time video transmission over urban multi-hop vehicular ad-hoc network
(VANET) scenarios. Queuing based mobility model, spatial traffic distribution and prob-
ability of connectivity for sparse and dense VANET scenarios are taken into consideration
in designing the routing protocol. Numerical results demonstrate the gain achieved by
the proposed routing scheme versus geographic greedy forwarding in terms of video frame distortion and streaming start-up delay in several urban communication scenarios for various vehicle entrance rate and traffic densities; and 3) finally, the proposed quality-driven
routing scheme for delivering video streams is combined with a novel IP management
scheme. The routing scheme aims to optimize the visual quality of the transmitted video
frames by minimizing the distortion, the start-up delay, and the frequency of the streaming freezes. As the destination vehicle is in motion, it is unrealistic to assume that the vehicle will remain connected to the same access router (AR) for the whole trip. Mobile IP management schemes can benefit from the proposed multi-hop routing protocol in order to adapt proxy mobile IPv6 (PMIPv6) for multi-hop VANET for video streaming applications. The proposed cross-layer protocols can significantly improve the video streaming quality in terms of the number of streaming freezes and start-up delay over VANETs while achieving low computational complexity by using pattern classification methods for optimization
PERFORMANCE EVALUATION OF SINGLE-HOP PERIODIC SAFETY BEACONING FOR VEHICLE-TO-VEHICLE COMMUNICATION IN V ANET
Saving human lives on road has become the prime objective of Vehicular Ad hoc
Network (VANET). In order to achieve safety, vehicles maintain neighborhood
awareness with the help of safety messages. Providing an efficient safety messaging
mechanism is a challenging task in V ANET, due to particular characteristics of
VANET, i.e. high mobility, limited channel bandwidth, very short communication
duration, and highly dynamic topology. In most of the safety messaging schemes
proposed so far, Periodic Safety Beacons (PSBs) are generally considered dispensable
in comparison with event-driven messages. However in reality, vehicle-to-vehicle
(V2V) PSBs are used to collect critical information required by all the safety
messaging schemes and cannot be dispensed. Thus, ensuring optimum QoS for V2V
single-hop PSBs is essential for achieving acceptable level of safety. However,
thorough performance evaluation ofV2V single-hop PSBs is yet to be carried out.
This research comprehensively investigates V2V single-hop periodic safety
beaconing in the light of tunable parameters i.e. Beacon Generation Interval (BGI),
Safety Beacon Size (SBS), and Communication Range (CR) that govern their
behavior. Results from exhaustive simulations show that adjusting tunable parameters
solely or combined does not fully satisfY the strict QoS criterion required for safety
applications. Overall, an acceptable level of end-to-end delay can be achieved by
dynamically adjusting tunable parameters with BGI > 1 OOms, but lower BGI is not
suitable with larger SBS. In dense traffic conditions strict PDR criterion of 99% is
never achieved beyond lOOm target CR. An exclusive comparison between tunable
parameters shows that solely adjusting BGI can attain relatively higher PDR than
other tunable parameters while SBS remains the least effective parameter. It is also
validated that dynamic adjustment of CR and BGI is necessary for optimal output in
terms of PDR. Furthermore, optimal combinations of tunable parameters for different
highway service levels with respect to safety application requirements are also
presented
Rate-Adaptation Based Congestion Control for Vehicle Safety Communications
This thesis deals with the scalability of Vehicle Safety Communications (VSC), where vehicles exchange periodic status messages to support future driver assistance applications. We systematically develop a design methodology for congestion control in VSC and present a resulting protocol named PULSAR. While previous works typically focused on controlling channel load only, we thereby integrate a concept which allows the adaptation to operate within the limits defined by safety applications