Ray-Optics Simulations of Outdoor-to-Indoor Multipath Channels at 4 and 14 GHz

Radio wave propagation simulations based on the ray-optical approximation have been widely adopted in coverage analysis for a range of situations, including the outdoor-to-indoor (O2I) scenario. In this work we present O2I ray-tracer simulations utilizing a complete building floor plan in the form of a point cloud. The ray-tracing simulation results are compared to measured channels at 4 and 14 GHz in terms of large scale parameters, namely path loss, delay spread and angular spread. In this work we address the importance of 1) interior walls and propagation paths originating therein, and 2) site-specific knowledge of window structure in accurately reproducing the O2I channel, particularly the presence of a thin insulating metal film on the windows. The best agreement between measurements and simulations was observed for the most detailed simulation. For both frequencies a mean error of less than 1.5 dB is reached for path loss, and a relative error of less than 10% for delay and angular spreads. Not including the metal film in simulations increases error of estimated building entry loss considerably, whereas absence of interior walls is detrimental to reproduction of large scale parameters.