A logically centralized slotted ALOHA-based scheme for broadcast services in vehicular ad hoc networks

In the vehicular ad hoc networks, a slotted ALOHA-based scheme for effective broadcast services is essential to disseminate the control and safety packets since it can avoid the slot collision issues. Existing slotted ALOHA-based schemes, for example, VeMAC, simply abandon the conflicting slots for all the collided nodes, which leads to a high collision probability and low wireless resource utilization. To address this issue, a logically centralized slotted ALOHA-based (LC-SA) scheme is proposed in this article. Different from the traditional slotted ALOHA-based schemes, the proposed LC-SA scheme solves the slot release problem and improves the rate of successful channel access. In the LC-SA scheme, a control node is enabled to reserve time slots for its neighbor nodes. In this way, a collided node within the communication range of the control node will continue to acquire this time slot if a collision is implied, while other collided nodes out of range will release this time slot to prevent another collision. Simulation results in both perfect and imperfect channel conditions are presented. The LC-SA scheme is verified to have higher throughput than VeMAC, due to more a rapid channel access speed and fewer access collisions.