Advise on tool to simulate multipath fading and pathloss (site-specific)

Hi all,

My project is to calculate and simulate “free space pass loss” and “multipath fading” of milimeter wave 28Ghz and 38 Ghz


Transmit and receiver antennas are located on top of 5 buildings inside my university (site-specific)
I have to calculate scattering, reflection of the wall, brick …
Problems: That kind of requiments had me build 3D (any other way ??). I tried SketchUp to make 3D building but I got stuck, I can only calculate distances.

I’m so confused, assume that I did build those 3D buildings, then what should I do next ? How could I trace the multipath rays ?

Please give me some advise, thank you so much