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Congestion Control in Vehicular Ad Hoc Networks

Stanica, Razvan. Congestion Control in Vehicular Ad Hoc Networks. PhD, Institut National Polytechnique de Toulouse, 2011

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Official URL: http://ethesis.inp-toulouse.fr/archive/00001749/

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.

Item Type:PhD Thesis
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Institution: Université de Toulouse > Institut National Polytechnique de Toulouse - INPT
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Research Director:
Beylot, André-Luc and Chaput, Emmanuel
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Deposited By: admin admin
Deposited On:21 Nov 2012 12:18

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