As new wireless standards are developed, the use of higher operation frequencies comes in hand with new use cases and propagation effects that differ from the well-established state of the art. Numerous stochastic fading models have recently emerged under the umbrella of generalized fading conditions to provide a fine-grain characterization of propagation channels in the mmWave and sub-THz bands. For the first time in literature, this work carries out an experimental validation of a class of such ray-based models in a wide range of propagation conditions (anechoic, reverberation and indoor scenarios) at mmWave bands. These models allow to characterize the communication channel with a reduced number of physically interpretable parameters. In specific, we show that the independent fluctuating two-ray (IFTR) model has good capabilities to recreate rather dissimilar environments with high accuracy and only four parameters. We also put forth that the key limitations of the IFTR model arise in the presence of reduced diffuse propagation, and also due to a limited phase variability for the dominant specular components.

The recent boom of 5G networks, coupled with the escalating demand among users for higher-capacity connections, is presenting a formidable challenge. 5G networks encompass a diverse array of advantageous technologies, prominently including Software- Defined Networking (SDN) together with Network Function Virtualization (NFV), in which a key problem is the optimal development of Service Function Chaining (SFC). This paper presents two approaches based on Genetic Algorithms (GAs), for the optimal composition of SFCs focused on network pathways, and tailored for the service chain required in different 5G connections (user service requests). The approaches have been tested on different instances of the problem with topologies including 6, 19 and 52 nodes. The obtained results are promising, showing optimal paths inside simple and complex topologies for every connection as well as for multiple connections.

In this paper, we present an analytical framework for the joint characterization of the 3D direction of arrival (DoA), i.e., azimuth and elevation components, and time of arrival (ToA) in multipath environments. The analytical framework is based on the use of nearly frequency-invariant beamformers (FIB) formed by toric arrays. The frequency response of the toric array is expanded as a series of phase modes, which leads to azimuth–time and elevation–time diagrams from which the 3D DoA and the ToA of the incoming waves can be extracted over a wide bandwidth. Firstly, we discuss some practical considerations, advantages and limitations of using the analytical method. Subsequently, we perform a parametric study to analyze the influence of the method parameters on the quality of the estimation. The method is tested in single-path and multipath mm-wave environments over a large bandwidth. The results show that the proposed method improves the quality of the estimation, i.e., decreases the level of the artifacts, compared to other state-of-art FIB approaches based on the use of single/concentric circular and elliptical arrays.

This paper presents a general technique for the joint Direction-of-Arrival (DoA) and Time-of-Arrival (ToA) estimation in multipath environments. The proposed ultra-wideband technique is based on phase-mode expansions and the use of nearly frequency-invariant elliptical arrays. New possibilities open with the present approach, as not only elliptical, but also circular and linear (highly flattened) arrays can be considered with the same implementation. Systematic selection/rejection of signals-of-interest/signals-not-of-interest in smart wireless environments is possible, unlike with previous approaches based on circular arrays. Concentric elliptical arrays of many sizes and eccentricities can be jointly considered, with the subsequent improvement that entails in DoA and ToA detection. This leads to the realization of pseudo-random array patterns; namely, quasi-arbitrary geometries created from the superposition of multiple elliptical arrays. Some simulation and experimental tests (measurements in an anechoic chamber) are carried out for several frequency bands to check the correct performance of the method. The method is proven to give accurate estimations in all tested scenarios, and to be robust against noise and position uncertainty in sensor placement.

There are some open issues concerning the optimal MRI imaging in terms of the RF signal acquisition. They are either related to the inhomogeneity of the radiation pattern of the receiving antennas or the design efficiency of the receiving antennas, among other relevant aspects. This document contains a study of the inhomogeneity reduction for near-field acquisition in high resolution MRI systems. It is proposed to progressively vary the antenna amplitude and phase feeding in the array distribution. It is proved that the progressive modification in the phase at each array ring reduces the pattern ripples, and optimal values for this progressive phase variation can be calculated, depending on the particular dimensions of the cylinder under test.

While many different simulation tools are available to compute MIMO capacity and diversity gain system performance, few works tackle the problem from the measurements standpoint. In this paper, several measurements of MIMO capacity and diversity gain performance of dipole antenna arrays are performed through the use of a reverberation chamber, which includes many effects present in real MIMO channels but generally avoided in simulations. Results show that polarization diversity can be effectively combined to spatial diversity even for Rayleig-fading MIMO scenarios to achieve increased diversity gain and MIMO capacity.

While many different simulation tools are available to compute MIMO capacity and diversity gain system performance, few works tackle the problem from the measurements standpoint. In this paper, several measurements of MIMO capacity and diversity gain performance of dipole antenna arrays are performed through the use of a reverberation chamber, which includes many effects present in real MIMO channels but generally avoided in simulations. Results show that polarization diversity can be effectively combined to spatial diversity even for Rayleigh-fading MIMO scenarios to achieve increased diversity gain and MIMO capacity.