Performance analysis of the IEEE 802.11 MAC protocol for DSRC with and without retransmissions

We develop an accurate analytical model for a dedicated short range communication (DSRC) network that uses the IEEE 802.11 distributed coordination function (DCF) MAC protocol, as adopted by the forthcoming IEEE 802.11p specification for DSRC. The specific focus is on broadcast vehicle-to-vehicle safety messages. We derive explicit expressions for the mean of the total packet delay and the packet delivery ratio (PDR) in an unsaturated network formed by moving vehicles on a highway. Our model is validated using extensive simulations and we show that our model yields better predictive accuracy than other existing models. The model is then used to investigate the performance of a modified DCF that uses a fixed number of sequential retransmissions to improve the reliability of packet delivery. We find that with sequential retransmissions, the PDR improves at low vehicle density (i.e. low traffic load), but degrades at heavy loads where higher collisions induced by the retransmissions outweighs the benefit of repeated attempts.