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A new method to include stochastic rough surface scattering into deterministic ray-optical wave propagation modeling is derived. It can be utilized in conjunction with the concept of ray launching. Similar to the Kirchhoff formulations, the approach is based on a tangential plane approximation, i.e., it is applicable to surfaces with gentle undulations, whose horizontal dimensions are large compared to the incident wavelength. However, in contrast to the Kirchhoff models, which are only valid for either slightly rough or very rough surfaces, the proposed stochastic scattering approach includes both the coherent and incoherent components at the same time. The purely deterministic ray-based modeling is expanded by a 'stochastic' component, allowing for the first time to account for nondeterministic scattering in ray-optical wave propagation modeling. Index Terms--Kirchhoff approximation, ray launching, ray tracing, ray-optical propagation modeling, rough surface scattering.

This work is concerned with the calculation of natural electromagnetic (EM) wave propagation and the determination of the propagation channel characteristics in highway or railway tunnels in the ultrahigh-frequency (UHF) range and above ([is greater than] 300 MHz). A novel ray-tracing technique based on geometrical optics (GO) is presented. Contrary to classical ray tracing, where the one ray representing a locally plane wave front is searched, the new method requires multiple representatives of each physical EM wave at a time. The contribution of each ray to the total field at the receiver is determined by the proposed ray-density normalization (RDN). This technique has the further advantage of overcoming one of the major disadvantages of GO, the failure at caustics. In contrast to existing techniques, the new approach does not use ray tubes or adaptive reception spheres. Consequently, it does not suffer their restrictions to planar geometries. Therefore, it allows to predict the propagation of high-frequency EM waves in confined spaces with curved boundaries, like tunnels, with an adequate precision. The approach is verified theoretically with canonical examples and by various measurements at 120 GHz in scaled tunnel models. Index Terms--Geometrical optics (GO), measurements, millimeter waves, mobile communications, ray launching, ray tracing, tunnels, wave propagation.

A novel numerical algorithm based on the radiative transfer equation (RTE) is presented, which allows the calculation of the scattering and penetration of isolated vegetation specimens such as, e.g., single trees, bushes, etc., at mm-wave frequencies. For this purpose, the RTE is stated in a discrete form, and the vegetation structure is discretized in elementary volumes. A step-by-step solution is proposed to solve for the desired attenuation, and indications on the influence of the different parameters on the propagation characteristics are given. A qualitative justification to the approach is presented and finally, a comparison with scattering measurements of ficus trees at 75 GHz is shown. Index Terms--Millimeter wave propagation, RTE, vegetation loss, volume scattering.

Future intelligent transportation systems (ITSs) will deeply rely on millimeter waves for communication and sensing purposes. This results in the need of a precise description of the propagation properties at these frequencies. In this paper, the propagation mechanisms reflection and diffraction of millimeter waves at realistic road surfaces and geometries are investigated theoretically and validated by measurements at 77 GHz. The effect of guided waves underneath a vehicle's underbody is observed, which can be exploited in a favorable way for range extension in obstructed sight situations. It is also shown that the local curvature of common road surfaces leads to focusing and defocusing effects of the transmitted energy, resulting in all increased signal fluctuation. Furthermore, the importance of diffraction phenomena at road crests is stressed, which were formerly neglected but may play all important role in security sensitive applications like collision avoidance systems etc. Index Terms--Automatic cruise control (ACC), automotive radar, ground reflection, interference, intervehicle communications, intelligent transportation system (ITS), millimeter waves, near grazing incidence.

A measurement campaign has been carried out in the Berlin subway to characterize electromagnetic wave propagation in underground railroad tunnels. The received power levels at 945 and 1853.4 MHz are used to evaluate the attenuation and the fading characteristics in a curved arched-shaped tunnel. The measurements are compared to ray-optical modeling results, which are based on ray density normalization. It is shown that the geometry of a tunnel, especially the cross-sectional shape and the course, is of major impact on the propagation behavior and thus on the accuracy of the modeling, while the material parameters of the building materials have less impact. Index Terms--Geometrical optics, measurements, mobile communications, ray launching, ray tracing, subway, tunnels, wave propagation.