  In vehicle-to-vehicle (V2V) channels, such roadside scatterers (RSSs) as
houses, buildings, trees, and many more, play a crucial role in the
determination of the Doppler power spectral density (DPSD) characteristics.
However, the relevant research results are scarce due to the lack of
computationally tractable analytic DPSD solutions. To fill this gap, we
investigate an indirect method for the DPSD analysis of a generic
two-dimensional (2D) RSS model for V2V channels. The indirect method, based on
the Hoeher's theorem, employs successive transformations of random variables to
obtain the DPSD. Compared to the conventional methods, leading to impractical
multiple integral solutions, our method yields a single integral-form, more
useful for analytic studies, model validation/parameter estimation, and fading
simulator design. Using the new DPSD solution, the impact of different RSS
layouts on the DPSD characteristics is further investigated, and several new
insights are provided. The joint probability density function (PDF) of
angle-of-departure and angle-of-arrival (AoA) and the joint Doppler-AoA PDF are
newly presented in closed-forms and analyzed with respect to the DPSD shape.
Comparisons with the DPSDs measured in highway and \FB{urban canyon}
environments demonstrate not only the validity of the generic 2D RSS model, but
also the significant contribution of RSSs to V2V channels.
