EM.Terrano In A Nutshell

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A Quick Introduction To SBR Simulation

EM.Terrano is a simulation software tool for modeling radio wave propagation in large scenes like urban canyons, indoor environments and natural terrain. Full-wave numerical methods like the finite difference time domain (FDTD) or the method of moments (MoM) solve differential or integral forms of Maxwell’s equations that require a fine discretization of the physical structure. To ensure the accuray of the simulation results, the resolution of the structure’s mesh must be high enough to accommodate a large number of cells per effective wavelength. Wireless propagation problems, on the other hand, typically involve scenes that may extend by hundreds or thousands of wavelengths. Generating a full-wave mesh in such scenarios can easily lead to intractable computational problems demanding terabytes of computer memory. Asymptotic methods such as Shoot-and-Bounce-Rays (SBR) offer a practical solution for large-scale problems of this type. EM.Terrano’s simulation engine is based on the SBR method, which combines Geometrical Optics (GO) with the Uniform Theory of Diffraction (UTD).

In EM.Terrano, a transmitter (acting as a source) shoots rays in all directions in the 3D space. The simplest source, however, is a short dipole radiator. The rays travel through the free space and are collected at the location of receivers (acting as field observation points). A ray is an electromagnetic energy tube with a triangular cross section that propagates in the channel medium along a certain direction vector. EM.Terrano models rays as fully polarimetric and coherent spherical waves that emanate from a source point and diverge (or spread) over distance undergoing both attenuation and phase change. In a simple free space channel, the tansmitted rays are directly picked up by the receivers.

In a more complex multipath environment with obstructions, rays may hit objects like buildings, walls, ground or terrain surface, etc. EM.Terrano discretizes the objects of your scene using a surface triangular mesh generator. This leads to a large number of flat triangular facets, which are hit by the incident rays. At the point of incidence on a facet, the incident ray reflects back into the scene. Part of the ray’s energy may also penetrate the surface and continue to propagate as a new transmitted ray. Edges of the obstructing buildings diffract the incident rays. As a result of diffraction, a large number of diffracted rays are generated in a conical configuration, which enter the scene and start to propagate as new independent rays. A simulation of a multipath channel usually involves thousands or even millions of propagating rays.


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