In vehicular ad hoc networks, many applications require a low latency and high reliability especially the safety applications. Reliable multi-hop broadcast protocols have been widely discussed recently. However, most of them use explicit acknowledgments and timeout retransmissions to provide reliability. The retransmission method incurs delays when a packet loss cannot be detected on time. Acknowledgment messages also increase the MAC layer contention time at each node. In order to provide a high reliability and low latency with a low overhead, we propose a mechanism which utilizes path diversity. In the proposed mechanism, a message is delivered through two different paths. By cooperation of these different paths, broadcast messages can be disseminated with a short delay and a high reliability compared with the acknowledgment based retransmission approach. Since the proposed mechanism does not use any explicit acknowledgment message, the message overhead is low. We evaluate the proposed mechanism using both theoretical analysis and computer simulations.
['Celimuge Wu', 'Satoshi Ohzahata', 'Toshihiko Kato']
A low latency path diversity mechanism for sender-oriented broadcast protocols in VANETs