Abstract
Decentralized Congestion Control (DCC) mechanisms have been a core part of protocol stacks for vehicular networks since their inception and standardization. The ETSI ITS-G5 protocol stack for vehicular communications considers the usage of DCC not only in the network or access layers, but also as a part of the cross-layer architecture that influences how often messages are generated and transmitted. ETSI DCC mechanisms have evolved from a reactive approach based on a finite state machine, to an adaptive approach that relies on a linear control algorithm. This linear control algorithm, called LIMERIC, is the basis of the mechanism used in the ETSI DCC Adaptive Approach. The behavior of this algorithm depends on a set of parameters. Different values for these parameters have been proposed in the literature, including those defined in the ETSI specification. A recent proposal is Dual- $\alpha $ , which chooses parameters to improve convergence and fairness when the algorithm has to react to fast changes in the use of the shared medium (transitory situations). This article evaluates, by means of simulations, the performance of the ETSI DCC Adaptive Approach and related algorithms, considering both steady state and transitory situations. Results show that a bad selection of parameters can make a DCC algorithm ineffective, that the ETSI DCC Adaptive algorithm performs well in steady state conditions, and that Dual- $\alpha $ performs as well in steady state conditions and outperforms the ETSI DCC Adaptive Approach in transitory scenarios.
Highlights
Network resources such as bandwidth are limited and subject to conditions that can vary from one moment to another
In the case of Vehicular Ad-Hoc Networks (VANETs), conditions can vary in many ways, e.g., one car can change from driving in a one-way street to merge into a busy boulevard, and this implies changes in the speed of the car and the way it interacts with other road users
The European Telecommunications Standards Institute (ETSI) ITSG5 protocol stack considers the use of Decentralized Congestion Control (DCC) mechanisms that apply on multiple layers [3], as do the standards established by the Society of Automotive Engineers (SAE International) [4]
Summary
Network resources such as bandwidth are limited and subject to conditions that can vary from one moment to another. The ETSI ITSG5 protocol stack considers the use of Decentralized Congestion Control (DCC) mechanisms that apply on multiple layers [3], as do the standards established by the Society of Automotive Engineers (SAE International) [4] These mechanisms try different approaches to DCC that range from limiting the rate at which vehicles generate and send messages, to limiting the power which vehicles use to transmit these messages, or a combination of both. In [5], simulations are used to compare the performance of the ETSI DCC Adaptive Approach and Dual-α in transitory scenarios In these simulations, the vehicles are static; only CAM traffic is present; and CAM message generation is at fixed intervals, independently of vehicle dynamics and feedback from DCC.
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