Analysis of event-driven warning message propagation in Vehicular Ad Hoc Networks

In order to increase the probability of delivering warning messages to all vehicles (or nodes) in the Zone Of Relevance (ZOR), Vehicular Ad Hoc Networks (VANETs) adopt the periodical broadcast to disseminate warning messages. The broadcast way brings the problem of how to set the suitable message lifetime for the propagation of the warning message. To tackle the aforementioned problem, this work adopts the following four steps to analyze the event-driven warning message propagation process and suggest a suitable message lifetime for the Vehicle-to-Vehicle (V2V) network. At first, an analytical model was proposed to investigate the event-driven warning message propagation process in a connected network, and thus assure that it is difficult to guarantee all nodes in the ZOR being in the same partition. Next, an analytical model was proposed to investigate the event-driven warning message propagation process in a partitioned network, and then the probability of delivering warning messages to all nodes in the ZOR for different traffic conditions is derived. Furthermore, to reduce redundancy caused by multi-hop broadcast, an direction-aware broadcast protocol was proposed for the partitioned network according to the proposed analytical models. At last, the impact of traffic characteristics on the setting of the suitable message lifetime was evaluated through numerical and simulation results. The results shown that the warning message propagation process depends on the traffic characteristics, e.g., nodes' density, nodes' speed and the dangerous time. The results also shown that when the message lifetime increases to certain values for different traffic conditions, the delivery probability is not increased, but just consuming power and causing serious redundancy. As a result, the work shown that the suitable message lifetime should be set according to the traffic condition of involved nodes.