Characterization of Carrier Sense Multiple Access in Vehicular Propagation Channels

Wireless communications between vehicles is considered to be one of the building blocks in order to increase the safety level offered by future intelligent transportation systems. While it sounds intuitively convincing that a periodic exchange of status information, e.g. the current position, speed and driving direction, may help to avoid dangerous traffic situations or driving maneuvers, it is not clear whether the envisioned communications system, i.e. IEEE 802.11p, is sufficiently reliable and robust. In particular, it is not clear whether the employed Carrier Sense Multiple Access (CSMA) mechanism employed at the medium access control (MAC) layer is able to coordinate concurrent access by multiple network nodes in a highly dynamic environment as intended. In this paper, we evaluate the performance of the CSMA-based coordination mechanism employed by IEEE 802.11p. The evaluation is based on a network simulation framework that emulates the signal processing steps of a transceiver and accurately models the multi-path propagation effects of the wireless vehicular radio channel. Due to this accuracy, the execution of such high fidelity simulations is computationally highly expensive and represents a prominent example of the discipline called Computational Science and Engineering (CSE). Based on the results of our evaluation, we come to the conclusion that CSMA is able to coordinate concurrent access in vehicular environments, even if fading radio propagation characteristics are present.