  Reconfigurable intelligent surface (RIS) can provide stable connectivity for
vehicular communications when direct transmission becomes significantly weaker
with dynamic channel conditions between an access point and a moving vehicle.
In this paper, we analyze the performance of a RIS-assisted vehicular network
by coherently combining received signals reflected by RIS elements and direct
transmissions from the source terminal over double generalized Gamma (dGG)
fading channels. We present analytical expressions on the outage probability
and average bit-error rate (BER) performance of the considered system by
deriving exact density and distribution functions for the end-to-end
signal-to-noise ratio (SNR) resulted from the finite sum of the direct link and
product of channel coefficients each distributed according to the dGG. We also
develop asymptotic analysis on the outage probability and average BER to derive
diversity order for a better insight into the system performance at high SNR.
We validate the derived analytical expressions through numerical and simulation
results and demonstrate scaling of the system performance with RIS elements and
a comparison to the conventional relaying techniques and direct transmissions
considering various practically relevant scenarios.
