Congestion Control for Vehicular Environments by Adjusting IEEE 802.11 Contention Window Size

The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-319-03889-6_30Medium access control protocols should manage the highly dynamic nature of Vehicular Ad Hoc Networks (VANETs) and the variety of application requirements. Therefore, achieving a well-designed MAC protocol in VANETs is a challenging issue. The contention window is a critical element for handling medium access collisions in IEEE 802.11, and it highly affects the communications performance. This paper proposes a new contention window control scheme, called DBM-ACW, for VANET environments. Analysis and simulation results using OMNeT++ in urban scenarios show that DBM-ACW provides better overall performance compared with previous proposals, even with high network densities.This work was partially supported by the Ministerio de Ciencia e Innovación, Spain, under Grant TIN2011-27543-C03-01Balador, A.; Tavares De Araujo Cesariny Calafate, CM.; Cano Escribá, JC.; Manzoni, P. (2013). Congestion Control for Vehicular Environments by Adjusting IEEE 802.11 Contention Window Size. En Algorithms and Architectures for Parallel Processing. Springer. 259-266. https://doi.org/10.1007/978-3-319-03889-6_30S259266Booysen, M.J., Zeadally, S., van Rooyen, G.-J.: Survey of media access control protocols for vehicular ad hoc networks. IET Communications 5(11), 1619–1631 (2011)Kenney, J.: Standards and regulations. In: Hartenstein, H., Laberteaux, K.P. (eds.) VANET: Vehicular Applications and Inter-networking Technologies, ch. 10, pp. 365–428. Wiley (2010)Stanica, R., Chaput, E., Beylot, A.-L.: Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel. In: 2011 IEEE International Conference on Communications (ICC), June 5-9, pp. 1–5 (2011)Calafate, C.T., Fortino, G., Fritsch, S., Monteiro, J., Cano, J., Manzoni, P.: An efficient and robust content delivery solution for IEEE 802.11p vehicular environments. Journal of Network and Computer Applications 35(2), 753–762 (2012)Cali, F., Conti, M., Gregori, E.: Dynamic tuning of the IEEE 802.11 protocol to achieve a theoretical throughput limit. IEEE/ACM Transactions on Networking 8(6), 785–799 (2000)Wu, H., Cheng, S., Peng, Y., Long, K., Ma, J.: IEEE 802.11 distributed coordination function (DCF): analysis and enhancement. In: IEEE International Conference on Communications, ICC 2002, vol. 1, pp. 605–609 (2002)Balador, A., Movaghar, A., Jabbehdari, S.: History based contention window control in ieee 802.11 mac protocol in error prone channel. Journal of Computer Science 6(2), 205–209 (2010)Chrysostomou, C., Djouvas, C., Lambrinos, L.: Applying adaptive QoS-aware medium access control in priority-based vehicular ad hoc networks. In: 2011 IEEE Symposium on Computers and Communications (ISCC), June 28-July 1, pp. 741–747 (2011)Jang, H.-C., Feng, W.-C.: Network Status Detection-Based Dynamic Adaptation of Contention Window in IEEE 802.11p. In: 2010 IEEE 71st Vehicular Technology Conference (VTC 2010-Spring), May 16-19, pp. 1–5 (2010)http://www.omnetpp.org/http://inet.omnetpp.org/Behrisch, M., Bieker, L., Erdmann, J., Krajzewicz, D.: SUMO - Simulation of Urban MObility: An Overview. In: The Third International Conference on Advances in System Simulation, SIMUL 2011 (2011)Baguena, M., Tornell, S., Torres, A., Calafate, C.T., Cano, J.C., Manzoni, P.: VACaMobil: VANET Car Mobility Manager for OMNeT++. In: IEEE International Conference on Communications 2013 - 3rd IEEE International Workshop on Smart Communication Protocols and Algorithms (SCPA 2013), Budapest, Hungary (June 2013)Baguena, M., Calafate, C.T., Cano, J., Manzoni, P.: Towards realistic vehicular network simulation models. In: 2012 IFIP Wireless Days (WD), November 21-23, pp. 1–3 (2012)http://www.openstreetmap.org

Network status detection-based dynamic adaptation of contention window in IEEE 802.11p

近年來，無線網路發展的成熟、行車安全問題的重視、全球定位系統的普及，以及車用網路(Vehicular Ad Hoc Networks, VANET)在研究上的前瞻性與未來的高應用價值，使得車用網路的發展也愈來愈受到各方的探討。然而，車用網路的拓撲變動性相當高且規模大，且屬於點對點(Ad-Hoc)的網路架構，因此，對於吞吐量(throughput)和碰撞率(collision)以及延遲時間(delay)皆有一定的需求。此外，由於車輛在道路上的分布容易造成訊號之間的碰撞和干擾，所以我們藉由修改RTS/CTS機制提出一個Detection-Based MAC，其機制可透過封包之間的訊息傳遞，偵測出網路的壅塞狀態，預測網路中鄰近節點的競爭情形，並依此來動態調整競爭視窗大小。最後，將此方法實作在IEEE 802.11p的媒體存取控制層(MAC)中，以解決車用網路節點互相干擾所造成的過多碰撞，並提升整體吞吐量。In recent years, the research on Vehicular Ad Hoc Networks (VANET) has been paid much attention due to the development of wireless network becoming mature, people think highly of traffic safety issues, the popularity of Global Positioning System (GPS), promising applications of VANET being exploited. However, VANET has the essential property of rapid change of large scale network topology. Besides, vehicles randomly distributed over the road usually causes serious signal collisions and interferences. Thus, it calls for special concerns to deal with the performances of throughput, collision, and delay. In this paper we propose a Detection-Based MAC mechanism by modifying RTS/CTS to detect network congestions through message exchange, and predict number of competing nodes. Both these information is used to dynamically adjust contention window sizes. Simulations are implemented on the MAC layer of IEEE 802.11p. The results show that the proposed method is able to effectively reduce collisions and increase overall throughput

Contrôle de Congestion dans les Réseaux Véhiculaires

Cette thèse analyse la possibilité d'utiliser des communications sans fil inter-véhiculaires pour améliorer la sécurité routière. Les performances du nouveau réseau ainsi créé (réseau ad-hoc véhiculaire) sont étudiées analytiquement et par des simulations dans un environnement réaliste. La thèse se concentre surtout sur des scénarios avec une forte densité de véhicules. Dans ce cas, l'accès au support devient un problème essentiel, en principal pour les applications de sécurité routière qui nécessitent une qualité de service élevée pour fonctionner dans un tel contexte. Ce travail montre que la version actuelle du standard IEEE 802.11, proposé comme méthode d'accès dans les réseaux véhiculaires, ne peut pas résoudre ce problème de passage à l'échelle pour supporter correctement les applications de sécurité routière. Plusieurs améliorations possibles sont analysées, liées à l'utilisation optimale de certains paramètres du protocole comme la taille de la fenêtre de contention ou bien le seuil de détection de la porteuse. Des nouveaux mécanismes adaptatifs visant ces paramètres sont proposés et les améliorations ainsi obtenues sont non-négligeables. Finalement, une nouvelle méthode d'accès est définie, en tenant compte des caractéristiques des applications de sécurité routière. Toujours basée sur des techniques CSMA, cette technique donne des résultats largement supérieurs à la version standard actuelle. ABSTRACT : The equipment of vehicles with wireless communication devices in order to improve road safety is a major component of a future intelligent transportation system. The success and availability of IEEE 802.11-based products make this technology the main competitor for the Medium Access Control (MAC) layer used in vehicle-to-vehicle communication. The IEEE 802.11p amendment has been specially designed in this special context of wireless access in vehicular environments. However, as all the other approaches based on Carrier Sense Multiple Access (CSMA), this protocol presents scalability problems, which leads to poor performance in high density scenarios, quite frequent in the case of a vehicular ad hoc network (VANET). This thesis studies the congestion control problem in the context of safety vehicular communications, with a special focus on the back-off mechanism and the carrier sense function. First of all, a number of important characteristics presented by the safety messages are discovered and understood by the means of an analytical framework. Second, the lessons learned from the analytical study are put into practice with the design of two adaptive mechanisms (one for the contention window and the other one for the carrier sense threshold) that take into account the local vehicular density. These mechanisms remain simple, but highly efficient, while also being straightforward to integrate in IEEE 802.11 devices. Finally, by taking into account the most important properties of a safety VANET, a new CSMA-based MAC protocol is proposed. This new access method, named Safety Range CSMA (SR-CSMA), relies on the idea that collisions can not be avoided in a high density network. However, by increasing the number of simultaneous transmissions between geographically distant nodes, SR-CSMA manages to better protect the immediate neighborhood, the most important area for safety applications