A-VeMAC: An adaptive vehicular MAC protocol for vehicular ad hoc networks

This paper proposes an adaptive vehicular MAC protocol, called A-VeMAC, for VANETs. A-VeMAC is a multichannel MAC protocol based on VeMAC. Like VeMAC, it employs a TDMA mechanism, and supports one control channel and several service channels. For the control channel, each frame is partitioned into two disjoint sets of timeslots, which are associated with vehicles moving in opposite directions, respectively. Unlike VeMAC, which equally partitions each frame, the frame partitioning with A-VeMAC is not equal. Instead, it can adaptively vary with the vehicle traffic conditions in opposite directions. The purpose is to better support unbalanced vehicle traffic conditions in opposite conditions. With A-VeMAC, a vehicle will first make an adjustment of frame partitioning based on the current traffic conditions in opposite directions before it attempts to reserve a timeslot. After the frame partitioning adjustment is completed, it will determine a set of timeslots that are available for it to reserve and then randomly selects one for reservation from the available timeslots. For the service channels, A-VeMAC employs the same access mechanism used in VeMAC. Simulation results show that A-VeMAC can well support both balanced and unbalanced vehicle traffic conditions, and can achieve a better performance than VeMAC in terms of the channel utilization and the access collision rate, in particular, under unbalanced traffic conditions.