Impacts of Point Cloud Modeling on the Accuracy of Ray-Based Multipath Propagation Simulations

This article reports the comparison of multipath channels of outdoor small cells at 28 GHz simulated by point-cloud-based ray tracer and those from measurements. The comparison shows that the ray tracer is capable of reproducing measured channels with reasonable accuracy, given proper permittivity values set for major building walls. The accuracy, however, depends on the types of point clouds we input to the ray tracer: 1) raw point cloud from laser scanning measurements of the cellular site; 2) flattened point cloud where structural details of the environments are all lost like what we find in publicly available digital maps; and 3) processed point cloud where missing sections are complemented, flat and rough sections of surfaces are identified and wedges are detected. For condensed parameters of channels such as path loss, delay, and angular spreads, ray tracing with the processed and raw point clouds shows equally good accuracy. In contrast, the ray tracing with the processed point cloud shows clear advantage of accuracy over that with the raw point cloud when simulating physical propagation paths. The raw point cloud produces many spurious paths that do not exist in measurements, whereas the processed point cloud reproduces multipath richness in form of many weak diffracted paths that are found in measurements and cannot be reproduced by diffuse scattering. Ray tracing with the flattened point cloud is in least agreement with measurements. Still, first-order specular reflections from large smooth walls are reproduced well by ray tracer with any of the tested point clouds. We thereby demonstrate the superiority of using the processed point cloud as inputs to ray tracer to obtain multipath channels with the highest fidelity to measurements.