Massive Multiple Input Multiple Output (MIMO) at millimeter-Wave (mmWave) frequencies is envisioned as a key technology for beyond 5G communication. Accurate channel modeling is crucial for the design and evaluation of such systems. Ray-Tracing (RT) can be used to accurately simulate the propagation channel. However, state-of-the-art RT for multi-antenna systems typically employs plane-wave extension under far-field conditions, failing to capture Near-Field (NF) and Spatial non-Stationary (SnS) properties that are observed in real-world mmWave massive MIMO channel measurements. This work aims at accurate and efficient RT simulations for massive MIMO systems, with a proposed coarse-refinement strategy capable of capturing NF and SnS. The channel is simulated using RT on a few sparsely located array elements and then interpolated onto other elements using spherical/astigmatic-wave approximation and the Uniform Theory of Diffraction, thus significantly reducing simulation complexity while maintaining accuracy. The proposed strategy is demonstrated to offer almost the same simulation accuracy as the brute-force method, with a dramatic reduction in complexity through experimental validation. The significance, novelty, effectiveness, and simplicity of the proposed framework make it highly valuable for massive MIMO channel research.

Unmanned Aerial Vehicles (UAV), also known as “drones”, are attracting increasing attention as enablers for many technical applications and services, and are emerging as a promising feature for constructing the next-generation mobile networks, with a special focus on the extension of coverage and capacity of mobile radio networks for 5G applications. In this paper we tackle this challenge and we aim at investigating the narrowband properties of the air-to-ground propagation channel by means of GPU accelerated ray launching simulations carried out in an urban environment for 5G communications.

A measurement campaign has been carried out in a reference indoor environment - a medium-size meeting room - using an ultra-wideband channel sounder operating at 3 different frequency bands: 10 GHz, 60 GHz and 300 GHz. Automatic rotational units are used at Tx and Rx side to perform a full horizontal scanning with directional antennas, in order to achieve a double-directional channel characterization. Preliminary results show that multipath is mainly affected by few single or double-bounce components, and significant contributions may come from objects other than the walls, e.g. TV monitor and entrance door. Most of the contributions are clearly identifiable at all the considered frequencies, although they appear to be stronger at 60 GHz compared to 10 GHz. The radio channel's multipath richness appears to be frequency dependent, and in particular it decreases when comparing 60 GHz to 300 GHz.

Graph theory-based channel modeling is an efficient approach to simulate multipath propagation taking into account the reverberation of electromagnetic waves. In this contribution, without modifying the modeling framework, we proposed a semi-deterministic graph modeling approach by associating the scatterers with realistic environment objects, and by calculating the coefficients of the propagation paths on the base of a proven diffuse scattering theory. An isolated office building scenario is adopted to illustrate the procedure of the proposed method. The performance is thus evaluated by comparing the simulated power-delay-profiles (PDPs) with ray-tracing and real channel measurement data. The results illustrate that the proposed method can accurately predict both the decaying slopes and the diffuse tails of the PDPs.

A Ray Tracing (RT) algorithm has been developed to predict the amount of solar radiation incident on the façades of buildings in urban environments. Such algorithm can be used to estimate the amount of solar energy turned into heat energy which contributes to the Urban Heat Islands (UHI) effect, to evaluate the energy efficiency of solutions like solar captators and, therefore, to estimate the overall energy efficiency of an urban area.

The polarimetric characteristics of the signal back scattered from a building wall are studied in this paper with the aid of MIMO measurements and Ray Tracing simulation. A very simple environment with a single rural building amid an open area is considered to reduce complexity and better isolate the different kinds of back-scattered contributions: specular reflection, diffractions, diffuse scattering. Narrowband and wideband metrics are utilized to evaluate scattering characteristics focusing in particular on its polarization properties.

The performance of space and frequency diversity techniques at 1800 MHz in an indoor environment are investigated. Three linear signal combining techniques are considered: signal selection (SEL), maximal ratio combining (MRC), and equal gain combining (EGC). The computations of received fading envelopes are performed by means of an analytical model, based on a three-dimensional ray-tracing (RT)/uniform theory of diffraction (UTD) technique; the reliability of the adopted approach is confirmed by comparison with some test measurements. The electromagnetic field components are adequately processed to obtain the single branch and combined signal envelope. The results show the very significant benefits that can be achieved both in terms of diversity gain and diversity advantage for both diversity techniques. Antenna spacings of about 0.75-1/spl lambda/ are nearly sufficient for achieving optimum performance, whereas frequency separation on the order of 10 MHz is needed for sufficiently decorrelated transmission on the two carriers.

Future wireless personal communications will find important applications in indoor environments; hence, an accurate analysis of the propagation characteristics within buildings and their impact on system design parameters is highly desirable. The performance of space diversity techniques in an indoor environment is investigated. Three linear signal combining techniques are considered: signal selection, maximal ratio combining and equal gain combining. The calculation of received fading envelope in the environment has been performed by using a 3D ray-tracing/UTD technique. The obtained results show the very significant benefits that can be achieved both in terms of diversity gain and diversity advantage, as well as the good agreement with the general achievements of previous experimental works.