Inter-vehicle communication (IVC) protocols have been studied to provide safe and comfortable driving. Each vehicle using the IVC protocols periodically broadcasts its current information (location, moving direction, speed, etc.), and other vehicles must receive such information exactly and in time. Other vehicles use received information to alert, advise, and navigate drivers, helping them become aware of the existence of other vehicles. This kind of application is helpful in various situations. For example, when a driver is approaching an intersection, the driver is not aware of vehicles that are also approaching the same intersection from another direction. To realize such inter-vehicle communication, we need to consider many issues such as protocol design, wireless standard, evaluation methodology, etc. Previous works on both mobile ad hoc networks and inter-vehicle communications used conventional metrics, e.g., packet delivery ratio, average delay, and path optimality, to study the performance of protocols. However, such metrics cannot be applied to inter-vehicle communications directly because the identities of the prospective receivers are a priori unknown. Moreover, many requirements must be considered to judge whether a IVC protocol satisfies the objectives of IVC applications. Although a vehicle get information properly, it is useless if that information arrives too late. This paper proposes new performance metrics to evaluate IVC protocols by the means of reliable and timely communications. We also introduce a methodology to perform realistic evaluation through simulation. Realistic vehicular traces and simulation models are required to get correct evaluation results.
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