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A ray-tracing method for predicting delay spread in tunnel environments

Our model to predict the propagation is based on ray-tracing which uses an images algorithm to find paths between transmitter and receiver of a digital communication system. It accounts for all rays reaching the receiver location after an arbitrary number of reflections and includes the effect of the angle of incidence, the material dielectric constant, the antenna pattern and polarization, the wall roughness, and the tunnel cross section size. The simulation results in this paper are obtained by analyzing many fewer rays compared to other published results. The results illustrate that in an empty straight rectangular tunnel environment, propagation has a very short time delay spread. Meanwhile, the results have shown that rms delay spread for horizontally polarized transmit and receive antennas is more than for vertically polarized transmit and receive antennas, in which the attenuation constant is less when transmit and receive antennas are horizontally polarized than when they are vertically polarized. Finally, by using a specific pattern, the rms delay spread is decreased compared to an isotropic antenna.