Evaluation of Time-Space Efficiency in CSMA/CA and Slotted Vanets

Recently slotted protocols have been demonstrated to work also in a distributed way and in a vehicular scenario. In particular one of them, MS-Aloha, has shown interesting scalability features. Despite a comparative analysis between CSMA/CA (IEEE 802.11p) and MS-Aloha has already been proposed in a simplified topology, a deep analysis on the efficiency of the two protocols has not been achieved: in this paper such analysis is split into the two separate domains of space and time. Results confirm that the slotted approach is more efficient and deterministic thanks to a joint time-space coordination driven by spatial slot assignment and reuse.