  Vehicular communication is characterized by a dynamic environment, high
mobility, and comparatively low antenna heights on the communicating entities
(vehicles and roadside units). These characteristics make vehicular propagation
and channel modeling particularly challenging. In this article, we classify and
describe the most relevant vehicular propagation and channel models, with a
particular focus on the usability of the models for the evaluation of protocols
and applications. We first classify the models based on the propagation
mechanisms they employ and their implementation approach. We also classify the
models based on the channel properties they implement and pay special attention
to the usability of the models, including the complexity of implementation,
scalability, and the input requirements (e.g., geographical data input). We
also discuss the less-explored aspects in vehicular channel modeling, including
modeling specific environments (e.g., tunnels, overpasses, and parking lots)
and types of communicating vehicles (e.g., scooters and public transportation
vehicles). We conclude by identifying the underresearched aspects of vehicular
propagation and channel modeling that require further modeling and measurement
studies.
