A publish-subscribe based framework for event notification in vehicular environments

In this work, we consider a vehicular environment in which vehicles moving along roads in a city are interested in different types of information or events generated at different parts of the city. We investigate the use of the publish-subscribe framework for such environments in which vehicles subscribe to a service provider for specific types of events through roadside units; the events are also reported to the service provider. The service provider delivers the events to the subscribed vehicles within the validity periods of both the subscriptions and the events through roadside units placed along the trajectory of a vehicle. We propose a problem called the Minimum Cost Event Placement Problem which addresses the issue of delivering all the events to all the subscribed vehicles within the validity periods while incurring minimum cost of utilization of the roadside units. We first prove that the problem is NP-complete. We then propose three heuristic algorithms to solve the problem. A lower bound on the cost of utilization of the roadside units for a given set of subscriptions and events is presented next. Detailed simulation results in different city traffic scenarios are presented to show that the costs achieved by two of the heuristics proposed are close to the lower bound proved.