Path loss revisited using computer simulation

In this paper, we propose a computer simulation model for the study of the large-scale effects on narrowband wireless transmission systems. The development of the path loss model is based on the ray tracing technique. This study concentrates on the first-order scattering effects, namely each multipath signal is a two-hop signal that involves a single scattering object. The first hop is directed toward the scatterer from the transmitter; and the second hop goes from the scatterer to the receiver. For each hop the signal is described using a two-ray model accounting for wave propagation along the direct path and along the ground-reflected path. The simulation results are consistent with the empirical models that are derived from measurements, including the Hata model and the Lee model. More importantly, two key observations are made: First, the path loss is affected by the number of scattering objects, their radar cross sections, and the ground reflection. Second, coherent multipath signals can cause the path-loss exponent falling below 2, which corresponds to free-space propagation.