Vehicular networking has significant potential to enable diverse applications associated with traffic safety, traffic efficiency and infotainment. In this survey and tutorial paper we introduce the basic characteristics of vehicular networks, provide an overview of applications and associated requirements, along with challenges and their proposed solutions. In addition, we provide an overview of the current and past major ITS programs and projects in USA, Japan and Europe. Moreover, vehicular networking architectures and protocol suites employed in such programs and projects in USA, Japan and Europe are discussed.

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Abstract-Vehicular networking is an enabling technology for Intelligent Transportation Systems (ITS). Different types of vehicular traffic applications are currently being investigated. In this paper we briefly introduce the communication requirements of a Co-operative Adaptive Cruise Control (C-ACC) vehicular traffic efficiency application. Furthermore, we propose a Channel Busy Time model to evaluate the solution space of a vehicular beaconing system designed to communicate information both vital and sufficient for vehicular traffic applications and in particular for C-ACC. We identify that the solution space is three-dimensional. These dimensions being based on the number of nodes (or vehicles), the beacon generation rate of the nodes and the size (or duration) of a beacon message.Based on the Channel Busy Time model we derive boundaries and ranges of parameters within which the beaconing system can be adapted to meet the requirements of the C-ACC application.

Road throughput can be increased by driving at small inter-vehicle time gaps. The amplification of velocity disturbances in upstream direction, however, poses limitations to the minimum feasible time gap. This effect is covered by the notion of string stability. String-stable behavior is thus considered an essential requirement for the design of automatic distance control systems, which are needed to allow for safe driving at time gaps well below 1 s. Using wireless inter-vehicle communications to provide real-time information of the preceding vehicle, in addition to the information obtained by common Adaptive Cruise Control (ACC) sensors, appears to significantly decrease the feasible time gap, which is shown by practical experiments with a test fleet consisting of six passenger vehicles. The large-scale deployment of this system, known as Cooperative ACC (CACC), however, poses challenges with respect to the reliability of the wireless communication system. A solution for this scalability problem can be found in decreasing the transmission power and/or beaconing rate, or adapting the communications protocol. Although the main CACC objective is to increase road throughput, the first commercial application of CACC is foreseen to be in truck platooning, since short distance following is expected to yield significant fuel savings in this case.

The recently standardised IEEE 802.11p Wireless Access in Vehicular Environment (WAVE) protocol is envisioned to be used for Vehicle-to-Vehicle and Vehicle-to-Infrastructure communications. We provide an analysis of 802.11p's performance when used for the exchange of small status messages known as beacons. These beacons enable vehicles to establish a Cooperative Awareness from which many applications can draw their inputs. Applications have been proposed to increase safety, efficiency and comfort of future road traffic.This paper investigates the impact of adapting settings for the Contention Window (CW) based on the traffic density in order to increase the efficiency of the 802.11p broadcasts w.r.t. reception probability and delay with a focus on real-time vehicle control. In contrast to the literature available on adapting CW settings in unicast, we find that the initial CW value of 15 proposed in the IEEE 802.11p standard performs significantly well under almost all studied circumstances.