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Congestion control in vehicular ad hoc networks

Vehicular ad hoc networks (VANET) play an important role in future car-to-car communication systems and related applications like self-organizing traffic information systems (SOTIS), which are based on broadcast/geocast transmission schemes. Congestion control for VANETs has not been studied thoroughly so far - but this feature is extremely necessary for VANET applications and network performance. Due to the high mobility and the resulting highly dynamic network topology, congestion control needs to be performed in a decentralized and self-organized way, locally in each VANET node. This paper presents a novel concept for utility-based congestion control and packet forwarding in VANETs. The control algorithm uses an application-specific utility function and encodes the quantitative utility information in each transmitted data packet in a transparent way for all users within a local environment. A decentralized algorithm then calculates the "average utility value" of each individual node based on the utility of its data packets and assigns a share of the available data rate proportional to the relative priority. For performance evaluation, the proposed decentralized utility-based packet forwarding and congestion control (UBPFCC) is implemented on top of the IEEE 802.11 MAC protocol. Network simulations including vehicular mobility models demonstrate that UBPFCC avoids the typical starvation of some nodes inside the network and shows a significant increase of efficiency in information dissemination and fairness.