  High-rank line-of-sight (LOS) MIMO systems have attracted considerable
attention for millimeter wave and THz communications. The small wavelengths in
these frequencies enable spatial multiplexing with massive data rates at long
distances. Such systems are also being considered for multi-path non-LOS (NLOS)
environments. In these scenarios, standard channel models based on plane waves
cannot capture the curvature of each wave front necessary to model spatial
multiplexing. This work presents a novel and simple multi-path wireless channel
parametrization where each path is replaced by a LOS path with a reflected
image source. The model fully is valid for all paths with specular planar
reflections and captures the spherical nature of each wave front. Importantly,
it is shown that the model uses only two additional parameters relative to the
standard plane wave model. Moreover, the parameters can be easily captured in
standard ray tracing. The accuracy of the approach is demonstrated on detailed
ray tracing simulations at 28 GHz and 140 GHz in a dense urban area.
