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Received Jul 26, 2017; Revised Dec 17, 2017; Accepted Jan 2, 2018
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1. Introduction
The current state of wireless technology, particularly in the urban environment, requires methods to estimate, with high precision, the multipath propagation of wideband radio channels and to minimize the error of on-site measurements. Physical and numerical methods of ray tracing and uniform theory of diffraction (UTD) coefficients are precise and efficient in simulating the path loss in complex environments. The choice of diffraction coefficients is critical for predicting the diffraction signal amplitude. By comparing high-precision and approximate solutions for the diffraction coefficients in canonical problems, as well as in real environments, general observations can be made regarding the ray methods and UTD coefficients.
Ray tracing is one of the most used deterministic technique for propagation prediction. This technique is based in the launching of millions of optical rays. This set of rays interact with the obstacles of the environment modeling the multipath propagation. Each ray is unique and is analyzed individually; then its amplitude and direction is unpredictable due to the multiple diffraction and reflections. Therefore, the numerical methods used to estimate the electromagnetic fields must be robust and accurate for all types of conditions.
The UTD is an asymptotic solution largely used to predict scattering propagation in urban environments. The diffraction occurs when a ray encounters a wedge, which generates multiple new rays determined by a diffraction cone according to the Huygens principle.
The UTD formulation is rigorous because the diffraction coefficients and angular definitions are quite complex and have many exceptions, depending on the wedge geometry and the positions of the transmitter and receiver. Many heuristic coefficients have been proposed to solve this problem, and the first UTD coefficients were developed for perfectly conducting wedges [1].
Malyuzhinets developed a high-precision solution for wedge diffraction in non-perfectly conducting surfaces [2]. However, the proposed solution is not practical for predicting the propagation in real (complex) environments because it uses a special function that is difficult to calculate numerically for arbitrary wedge angles, but it is a useful reference to compare other...