Effects of Diffraction and Ground Reflection on Ray-Tracing-Based Coverage Predictions in Urban Microcellular Environments

Two-and-one-half dimensional ray tracing models, in combination with the uniform theory of diffraction and geometrical optics, are widely employed for propagation prediction in urban microcellular environments because of their high efficiency and reliable prediction accuracy. In this study, an improved ray tracing algorithm based on the “orientation face set” concept and on the improved 2D polar sweep algorithm is used. The aim of this paper is mainly to analyze the effects of different propagation mechanisms on ray-tracing-based coverage predictions in urban microcellular environments. In addition, the effects associated with the coverage prediction are visually represented.

I. Introduction

The growing demand for mobile communications, specially in urban areas, leads toward the adoption of the microcellular concept. It is then desirable to perform accurate coverage predictions in micro- and pico-cells to minimize on-site measurements [1]. The deterministic propagation models, which are principally based on numerical methods such as the ray tracing method and the finite-difference time-domain method [2], are developed and widely adopted. Ray tracing techniques as a site-specific prediction model can accurately predict the amplitude, delay, and direction of arrival of multipath echoes created by the propagation environment [3]. Ray tracing techniques are widely adopted, and their reliability and flexibility have been proven in urban environments [4]–[6]. Under urban microcellular environments, both transmitter and receiver are well below the rooftops [7]. In these environments propagation mechanisms may include direct, reflected, diffracted, and some combined rays. Therefore, it's very necessary to analyze the effects of different propagation mechanisms on ray-tracing-based coverage predictions. For this purpose, this study focused on analyzing the influence of diffraction and ground reflection on ray-tracing-based coverage predictions of path loss over a large area. Fig. 1.

Plan view of ottawa city core with one transmitter (marked by asterisks).