  Due to the dynamic nature of vehicular traffic and the road surroundings,
vehicle-to-vehicle (V2V) propagation characteristics vary greatly on both
small- and large-scale. Recent measurements have shown that both large static
objects (e.g., buildings and foliage) as well as mobile objects (surrounding
vehicles) have a profound impact on V2V communication. At the same time,
system-level Vehicular Ad Hoc Network (VANET) simulators by and large employ
simple statistical propagation models, which do not account for surrounding
objects explicitly. We designed GEMV$^2$ (Geometry-based Efficient propagation
Model for V2V communication), which uses outlines of vehicles, buildings, and
foliage to distinguish the following three types of links: line of sight (LOS),
non-LOS due to vehicles, and non- LOS due to static objects. For each link,
GEMV$^2$ calculates the large-scale signal variations deterministically,
whereas the small- scale signal variations are calculated stochastically based
on the number and size of surrounding objects. We implement GEMV$^2$ in MATLAB
and show that it scales well by using it to simulate radio propagation for
city-wide networks with tens of thousands of vehicles on commodity hardware. We
make the source code of GEMV$^2$ freely available. Finally, we validate
GEMV$^2$ against extensive measurements performed in urban, suburban, highway,
and open space environment.
