Performance Analysis of a MAC Protocol Consisting of EDCA on the CCH and a Reservation on the SCHs for the IEEE 802.11p/1609.4 WAVE

Abstract

We propose an analytical model for the medium access control (MAC) protocol that consists of an enhanced distributed channel access (EDCA) on the control channel (CCH) and a reservation method on the service channels (SCHs) for the IEEE 802.11p/1609.4 wireless access in vehicular environments of intelligent transportation systems. Specifically, a safety packet of a high priority and a request for service (RFS) of a low priority for the SCH reservation are serviced on the CCH with a contention-based EDCA mechanism; meanwhile, nonsafety applications such as map download and commercial advertisements are serviced on an SCH with a contention-free scheme through the reservation of an SCH from the handshaking of an RFS packet on the CCH. To satisfy the safety packet quality-of-service (QoS) requirements regarding a within-100-ms delay and a successful delivery probability higher than 98%, we assume that each on-board unit of a vehicle is equippedwith two transceivers, one of which always stays tuned on the CCH, while the other is tuned on the assigned SCH; furthermore, a roadside unit sends an acknowledgmentmessage to the broadcasted safety packets to guarantee a high successful delivery probability. By constructing multidimensional Markov chains for the proposed MAC, we derive the intended successful delivery probability and the delay distribution of both the safety packet and the RFS packet. Numerical results show that the QoS requirements for the safety packet are satisfied, i.e., safety packets can be delivered within 100 ms with a successful delivery probability above 98%, even when the number of vehicles reaches up to 150. We compare the results of our proposed contention-free access scheme in the SCH selected by reservation with those of a contention-based access scheme in the SCH selected by randomness.