Investigating the effectiveness of decentralized congestion control in vehicular networks

Vehicular ad hoc networks are expected to suffer from channel congestion, due to the high number of vehicles moving on the roads, the limited available bandwidth and the many applications that they will support. In order to mitigate such problem, ETSI has recently specified the Decentralized Congestion Control (DCC) mechanisms for Intelligent Transportation Systems (ITS) operating in the 5 GHz range. Although they are already part of the standard, very few results exist on the DCC performance. In this work, we aim at filling this gap by investigating the impact on the system performance of the single DCC mechanisms, as well as their joint effect when they are all implemented at the DCC access layer. Surprisingly, we find that DCC has little impact, and, in certain scenarios, it may even lead to performance degradation with respect to the case where the legacy IEEE 802.11p MAC protocol is implemented.