Link quality based EDCA MAC protocol for WAVE vehicular networks

The WAVE vehicular networks adopt the Enhanced Distributed Channel Access (EDCA) as the MAC layer protocol. In EDCA, different values of arbitrary inter-frame space (AIFS) can be used for different classes of traffic. The smaller the AIFS value is, the higher the priority a device has in accessing the shared channel. In this paper, we exploit the possibility of assigning the AIFS values according to channel/link quality. Notably a device with better link quality can transmit at a higher data rate. Therefore, our key objective is to maximize the system throughput between a roadside unit (RSU) and the onboard units (OBUs) passed by. Since IEEE 802.11p supports eight transmission rates, two schemes for mapping AIFS values to transmission rates are studied. The first one (8-level-AIFS) uses eight distinct AIFS values, one for each transmission rate. And the second one (4-level-AIFS) uses four distinct AIFS values, one for every two adjacent transmission rates. Their throughput performances are studied by simulations. It is interesting to note that OBUs tend to experience the same pattern of channel quality fluctuation, due to the similar vehicle moving pattern. To this end, assigning AIFS values according to link quality is fair.