Admission Control for Roadside Units Based on Virtual Air-Time Transmissions

Providing vehicles with different services is an important challenge for the Roadside Units (RSUs) to support future Intelligent Transportations Systems applications. In rush hours, tens of vehicles might request different services from a shared RSU. When the RSU becomes close to overloaded situations, the Admission Control (AC) and the resource allocation algorithms play very important role of determining whether accepting new arrivals affects the in-session tasks. Admitting more tasks means pushing their task finish time to their deadlines (RSU range leaving time), which increases the risk of the vehicles, thus, increasing the probability of task failure. In this paper, we propose an admission control and resource allocation algorithm that helps the RSU keep the number of admitted tasks higher, and at the same time reducing the risk of the tasks as the vehicles progress and move toward the edges of the RSU´s transmission range. The algorithm calculates the physical expected task finish time for those vehicles, but allocates a virtual air-time transmission plan, which includes an extra time called the backup time. This extra time can be used to download the remaining data in case the task could not be finished on time. This time can automatically be transferred to the air-time transmission plan of the next vehicle closer to leave the RSU region in case it was not used. Simulation results show that our algorithm maintains higher number of admitted tasks and at the same time reduces the failure rate of those tasks.