Abstract
Reliably broadcasting safety information to neighboring vehicles is a big challenge in vehicular ad-hoc networks (VANETs), due to the dynamic network topology and the unreliable wireless channels. In this paper we present two decentralized cooperative schemes to enhance broadcast reliability by exploiting the advantage of message piggybacking. The key idea is to let each vehicle optimally piggyback some messages it has received when broadcasting with the expectation that the neighboring vehicles can recover its lost messages through the piggybacked messages. We first present greedy piggybacking, in which each vehicle announces its lost messages to neighboring vehicles and makes piggybacking decisions based on message losses in its neighbors. We observed that some lost messages still cannot be successfully recovered in greedy piggybacking due to the asymmetric wireless communications, and further proposed a mutual learning based scheme to overcome the drawback of greedy piggybacking. We evaluated the performance of the two schemes through trace-driven simulations, and results show that both schemes can achieve significant improvement on broadcast reliability in VANETs in comparison with the existing solutions.