Effect of retransmissions on the performance of the IEEE 802.11 MAC protocol for DSRC

We propose and evaluate two retransmission-based schemes to improve the reliability of broadcasts in a contention-based MAC, with application to safety messages in dedicated short range communication (DSRC). These improve the reliability of event driven emergency messages without requiring feedback or additional protocol overhead. We also extend the Piggybacked ACK protocol into a feedback-based retransmission scheme. These three schemes can be implemented on top of the 802.11p MAC. We demonstrate by simulation that the packet delivery ratio of event messages is improved in diverse traffic conditions, with a small drop in performance for routine messages. We do not observe a significant improvement from using feedback, compared with the blind retransmission schemes.