Rapid Dissemination of Public Safety Message Flows in Vehicular Networks

We consider a Road Side Unit (RSU) that aims to broadcast critical public safety message flows to vehicles that travel along a linear highway. The RSU is able to transmit such message flows directly to only a limited group of vehicles travelling in its close vicinity. To assure delivery of these messages to all other vehicles traveling along the highway, we make use of a Vehicular Ad Hoc Network (VANET) system to provide vehicle-to-vehicle multi-hop transport of these messages. We propose a VANET networking scheme that is identified as a Vehicular Backbone Network (VBN), under which vehicles that are located close to properly selected nominal positions are elected to serve as Relay Nodes (RNs). We study the optimal cross-layer design of such a network system, by presenting an analytical model to jointly select the operational data rate, scheduling mechanism and the inter-RN targeted distance levels. We show that a high level of coverage of highway vehicles, coupled with very low incurred queueing delays, can be achieved by employing a flow admission control mechanism at the source. We consider a high intensity vehicular traffic flow regime under which vehicles that are elected to serve as RNs are generally located close to designated nominal positions, as well as lower rate stochastic traffic flow conditions. Furthermore, we demonstrate the capability of the system, when properly configured, to employ a vehicular Carrier Sense Multiple Access/ Collision Avoidance (CSMA/CA) access scheme to well emulate the operations of the system when managed by the use of spatial-reuse Time Division Multiple Access (TDMA) scheduling scheme. Our mathematical analyses and designs are well confirmed through the execution of system simulation analyses.