Decentralized congestion control in ETSI Intelligent Transport Systems and its effect on safety applications

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Decentralized Congestion Control (DCC) mechanisms are a crucial part of Intelligent Transport Systems (ITS) and Vehicular ad-hoc networks (VANETs). It is through the use of DCC that a network maximizes its throughput and efficiency by allocating resources (i.e., access to the medium) fairly in congestion situations. The ITS framework defined by the European Telecommunications Standards Institute (ETSI) considers the usage of DCC both in the Access layer and as part of a cross-layer architecture. This means that DCC mechanisms influence the performance of elements in different layers. One of the components that are directly influenced by DCC is the Cooperative Awareness (CA) basic service —the entity that keeps vehicles aware of the presence of each other on the road. In this thesis, we perform an analysis of the DCC mechanism defined by ETSI, particularly an analytical and experimental evaluation of the performance of the ETSI DCC Adaptive Approach algorithm, comparing it to related algorithms including our own proposal (Dual-alfa). Additionally, we present an evaluation of the effect of DCC on the end-to-end delay of the CA basic service, and propose Generate-on-Time (GoT), an addition to the standard that accounts for delays caused by DCC and the effects these delays bring on other metrics. Results from this thesis show that Dual-alfa is a valid addition to ETSI Adaptive DCC in order to account for transitory situations. Furthermore, the evaluation of Generate-on-Time showed that it improves the performance of Cooperative Awareness Messages (CAMs) when multiple types of traffic coexist.
Decentralized Congestion Control, DCC, European Telecommunications Standards Institute, ETSI, Intelligent transportation systems, Vehicular ad-hoc networks, VANETs
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