Abstract
In this manuscript, a computer simulation model for the study of the large-scale effects on narrowband transmission systems is proposed to validate the existing semi-empirical models. The development of the computer simulation path-loss model is based on the ray tracing technique. It is emphasized that multipath signals are considered in this model. This study only 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 (TX); and the second hop goes from the scatterer to the receiver (RX). Each hop signal is described using a two-ray model due to direct-path propagation and ground-reflected path propagation. When the number of scattering objects is large, the simulation results are consistent with the semi-empirical models that are based on measurements, including the Hata model, the Lee model, and the model reported in [3]. Typically, the path-loss increases linearly with log distance. However, when the number of scattering objects is small, the linear model for path loss is not universally valid. In particular, when the path loss and log distance are weakly correlated in a linear manner, the linear model may lead to physically unrealizable results. This observation has not been made by the various groups that studied channel modeling based on measurements. In addition, the proposed model enjoys the flexibility in studying the effects of scattering object density in the channel, the radar cross section of the scattering objects, the ground reflection coefficients, and the distance between the TX and the RX. Furthermore, coherent multipath signals can cause the path-loss exponent to fall below 2, which corresponds to free-space propagation.
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