Ray tracing propagation modeling for future small-cell and indoor applications: A review of current techniques

Abstract

Applied for the first time to mobile radio propagation modeling at the beginning of the nineties, ray tracing is now living a second youth. It is probably the best model to assist in the design and planning of future short-range, millimeter-wave wireless systems, where the more limited propagation environment with respect to UHF frequencies allows to overcome traditional high-CPU time limitations while the higher operating frequency makes ray-optics approximations less drastic and allows to achieve an unprecedented level of accuracy. An overview of ray tracing propagation modeling is given in this paper, with a special attention to future prospects and applications. In particular, frontiers of ray-based propagation modeling such as extension to diffuse scattering, multidimensional channel characterization, multiple-input multiple-output (MIMO) capacity assessments, and future applications such as real-time ray tracing are addressed in the paper with reference to the work recently carried out at the University of Bologna.

Analysis of In-Room mm-Wave Propagation: Directional Channel Measurements and Ray Tracing Simulations

“…While coherent interactions are tracked through a recursive, image-RT technique, diffuse scattering is implemented according to a ray launching (RL) approach, i.e., based on rays launched from the TX with a discrete angle step [11].…”

“…Software simulations in the measurements environment have been carried out with a 3D Ray Tracing (RT) tool specifically conceived for indoor environments and described with more details in [11]. In addition to the coherent interaction mechanisms modeled by geometrical optics (GO) and uniform theory of diffraction (UTD), i.e., specular reflection (simply labeled as BR^in the following), transmission (BT^) and diffraction (BD^), diffuse scattering (BS^) is also taken into account using the effective roughness (ER) model [11,25].…”

“…Software simulations in the measurements environment have been carried out with a 3D Ray Tracing (RT) tool specifically conceived for indoor environments and described with more details in [11]. In addition to the coherent interaction mechanisms modeled by geometrical optics (GO) and uniform theory of diffraction (UTD), i.e., specular reflection (simply labeled as BR^in the following), transmission (BT^) and diffraction (BD^), diffuse scattering (BS^) is also taken into account using the effective roughness (ER) model [11,25]. The ER model can be easily embedded into ray based prediction tools in order to approximately but effectively account for non-specular contributions generated by surface roughness, surface unevenness (e.g., protruding elements) and/or volume dishomogeneities (e.g., buried cables and pipes), often not included into the input databases to limit their size or because simply unknown.…”

“…Many studies have shown that scattering effects may be important at sub-6-GHz frequencies [11,16,17], because of the presence of many objects generating non-specular, scattered contributions due to their size being comparable to the wavelength, to surface unevenness or to volume dishomogeneities [18]. Whether diffuse scattering becomes stronger or-on the contrary-weaker at mm-wave with respect to lower frequencies is still under debate [19], and even conflicting analyses can be found in the literature.…”

“…This is usually achieved through measurement campaigns [9,10] or exploiting ray tracing (RT) prediction models [11][12][13][14], which can in principle simulate the multipath channel. It is worth noticing that the computation capabilities provided by today's multicore processors and graphical processing units (GP-GPUs) can cope with the computational burden required by RT simulations, thus partly removing the bottleneck that used to limit the massive use of RT models [15].…”