An adaptive MAC retransmission limit selection scheme is proposed to improve the performance of IEEE 802.11p MAC protocol for video streaming applications over vehicular area networks (VANETs). A multi-objective optimization framework is applied at road side unit (RSU) which jointly minimizes the probability of playback freezes and the start-up delay of the streamed video at the destination vehicle by tuning the MAC retransmission limit with respect to channel statistics as well as packet transmission rate.
Periodic channel state estimation is performed at RSU which is video transmitter by information acquired from received signal strength (RSS) considering Doppler shift effect. Also, estimation of access probability between RSU and destination vehicle is done via information about the most recent location of the vehicle and considered in design of adaptive MAC scheme. The information is enclosed inside the user datagram protocol (UDP) packet header. Compared with non-adaptive IEEE 802.11p MAC, our scheme results in significantly less playback freezes while introducing slight increase in start-up delay.