  Vehicle-to-Vehicle (V2V) communication is a core technology for enabling
safety and non-safety applications in next generation Intelligent
Transportation Systems. Due to relatively low heights of the antennas, V2V
communication is often influenced by topographic features, man-made structures,
and other vehicles located between the communicating vehicles. On highways, it
was shown experimentally that vehicles can obstruct the line of sight (LOS)
communication up to 50 percent of the time; furthermore, a single obstructing
vehicle can reduce the power at the receiver by more than 20 dB. Based on both
experimental measurements and simulations performed using a validated channel
model, we show that the elevated position of antennas on tall vehicles improves
communication performance. Tall vehicles can significantly increase the
effective communication range, with an improvement of up to 50 percent in
certain scenarios. Using these findings, we propose a new V2V relaying scheme
called Tall Vehicle Relaying (TVR) that takes advantage of better channel
characteristics provided by tall vehicles. TVR distinguishes between tall and
short vehicles and, where appropriate, chooses tall vehicles as next hop
relays. We investigate TVR's system-level performance through a combination of
link-level experiments and system-level simulations and show that it
outperforms existing techniques.
