Towards real-time media access in vehicular ad-hoc networks

By giving vehicles the ability to propagate warning messages to the other ones, the number and the severity of accidents on our streets could likely be reduced. Safety-related applications based on vehicular ad-hoc neworks (VANET) are usually dependent on transmitting a message from source to sink within a given time limit. IEEE proposes the standard 802.11p which is an adaption of the well-known Wireless LAN 802.11a for inter-vehicle communication. While many properties have been improved, 802.11p still comes with a contention-based medium access control, only. This leads to an indeterminism and data-dependencies. One deterministic and fairer alternative compared to contention based medium access mechanism would be Time-Divison Multiple Access (TDMA). As a VANET is typically fully self-organizing, the time slots must be assigned autonomously by the nodes of the distributed system. This, however, leads to drawbacks in the performance of the protoctol which are analyzed in this paper.