A-ADHOC: An Adaptive Real-time Distributed MAC Protocol for Vehicular Ad Hoc Networks

Vehicular Ad Hoc Networks (VANET) are the foundation of Intelligent Traffic System (ITS), and recently many MAC protocols for VANET are proposed, among which a reliable MAC protocol called ADHOC has aroused much attention. By investigating the details of ADHOC protocol, we have discovered several unsolved problems that might lead to network failure. In this paper, we provide a quantitative analysis of the success probability for contending nodes and prove that an adaptive frame length is quite necessary. We propose Adaptive-ADHOC (A-ADHOC) MAC protocol, which implements a robust mechanism supporting the adaptive frame length. Evaluation result shows that A-ADHOC can maintain a high contending success probability and obtain about 50% reduction of response time over original ADHOC protocol, while providing important enhancement on network scalability and robustness.