SBR IMAGE APPROACH FOR RADIO-WAVE PROPAGATION IN TUNNELS WITH AND WITHOUT TRAFFIC

In this paper we will propose a deterministic approach to model the ra dio propagation channels in tunnels with and without traffic. This tec hnique applies the modified shooting and bouncing ray (SBR) method to find equivalent sources (images) in each launched ray tube and sums th e receiving complex amplitude contributed by all images coherently. In addition, vector effective antenna height (VEH) is introduced to cons ider the polarization-coupling effect resulting from the shape of tunn els. We verify this approach by comparing the numerical results in two canonical examples where closed-form solutions exist. The good agreem ent indicates that our method can provide a good approximation of high -frequency radio propagation inside tunnels where reflection is domina nt. Work reported in this paper has shown that propagation loss in tun nels can vary considerably according to the shapes of tunnels and the traffic inside. From the results we also find a ''focusing'' effect, w hich makes the power received in an arched tunnel higher than that in a rectangular tunnel. Besides, the deep fading that appears in a recta ngular tunnel is absent in an arched tunnel. The major effect of traff ic is observed to be the fast fading due to the reflection/obstruction of vehicles. Additional considerations, such as time delay, wall roug hness, and wedge diffraction of radio wave propagation in tunnels are left for future studies.