Fair decentralized data-rate congestion control for V2V communications

Channel congestion is one of the most critical issues in IEEE 802.11p-based vehicular ad hoc networks because congestion may lead to unreliability of applications. As a counter measure, the European Telecommunications Standard Institute (ETSI), proposes a mandatory Decentralized Congestion Control (DCC) framework to control the channel load. DCC algorithms are proposed to tune parameters such as message-rate, data-rate, etc. to avoid congestion. An important requirement for DCC algorithms is fairness, which ensures that vehicles experiencing similar channel loads are entitled to similar transmission parameters, in particular, message-rate and data-rate. Message-rate DCC (LIMERIC) ensures a fair message-rate selection, while data-rate DCC (DR-DCC) might end up with different data-rates, creating unfairness among the vehicles: Vehicles with lower data-rate have a larger communication range than those using higher data-rates. Therefore some vehicles are less visible than others, which is detrimental to the reliability of the safety applications. To avoid this, the paper defines a novel packet-count based decentralized data-rate congestion control algorithm (PDR-DCC), which enforces fairness and hence improves the application-reliability. Simulation studies are performed to demonstrate that PDR-DCC avoids congestion in a fair manner. We also show the effect of fairness on the application-reliability by comparing the performance of PDR-DCC with message-rate (LIMERIC) and data-rate (DR-DCC) congestion control algorithms for a stationary vehicle warning application in a synthetic highway scenario and for various vehicular densities. We conclude that PDR-DCC outperforms LIMERIC, and DR-DCC in terms of application-reliability.