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The development of intelligent transportation systems (ITS), vehicular ad hoc networks (VANETs), and autonomous driving (AD) has progressed rapidly in recent years, driven by artificial intelligence (AI), the internet of things (IoT), and their integration with dedicated short-range communications (DSRC) systems and fifth-generation (5G) networks. This has led to improved mobility conditions in different road propagation environments: urban, suburban, rural, and highway. The use of these communication technologies has enabled drivers and pedestrians to be more aware of the need to improve their behavior and decision making in adverse traffic conditions by sharing information from cameras, radars, and sensors widely deployed in vehicles and road infrastructure. However, wireless data transmission in VANETs is affected by the specific conditions of the propagation environment, weather, terrain, traffic density, and frequency bands used. In this paper, we characterize the path loss based on the extensive measurement campaign carrier out in vehicular environments at 700 MHz and 5.9 GHz under realistic road traffic conditions. From a linear dual-slope path loss propagation model, the results of the path loss exponents and the standard deviations of the shadowing are reported. This study focused on three different environments, i.e., urban with high traffic density (U-HD), urban with moderate/low traffic density (U-LD), and suburban (SU). The results presented here can be easily incorporated into VANET simulators to develop, evaluate, and validate new protocols and system architecture configurations under more realistic propagation conditions.

The usage scenarios defined in the ITU-M2150-1 recommendation for IMT-2020 systems, including enhanced Mobile Broadband (eMBB), Ultra-reliable Low-latency Communication (URLLC), and massive Machine Type Communication (mMTC), allow the possibility of accessing different services through the set of Radio Interface Technologies (RITs), Long-term Evolution (LTE), and New Radio (NR), which are components of RIT. The potential of the low and medium frequency bands allocated by the Federal Communications Commission (FCC) for the fifth generation of mobile communications (5G) is described. In addition, in the Internet of Things (IoT) applications that will be covered by the case of use of the mMTC are framed. In this sense, a propagation channel measurement campaign was carried out at 850 MHz and 5.9 GHz in a covered corridor environment, located in an open space within the facilities of the Pedagogical and Technological University of Colombia campus. The measurements were carried out in the time domain using a channel sounder based on a Universal Software Radio Peripheral (USRP) to obtain the received signal power levels over a range of separation distances between the transmitter and receiver from 2.00 m to 67.5 m. Then, a link budget was proposed to describe the path loss behavior as a function of these distances to obtain the parameters for the close-in free space reference distance (CI) and the floating intercept (FI) path loss prediction models. These parameters were estimated from the measurements made using the Minimum Mean Square Error (MMSE) approach. The estimated path loss exponent (PLE) values for both the CI and FI path loss models at 850 MHz and 3.5 GHz are in the range of 2.21 to 2.41, respectively. This shows that the multipath effect causes a lack of constructive interference to the received power signal for this type of outdoor corridor scenario. These results can be used in simulation tools to evaluate the path loss behavior and optimize the deployment of device and sensor network infrastructure to enable 5G-IoT connectivity in smart university campus scenarios.

In this paper, a comparative analysis between concentrated and distributed massive multiple-input multiple-output channels (C-mMIMO and D-mMIMO respectively), in an indoor environment using ray-tracing (RT) in the 26 GHz band is presented. The comparison is carried out in a realistic scenario consisting of a floor of a large building. The simulations emulated the up-link channel in an indoor cell in the framework of a time division duplex (TDD) - orthogonal frequency division multiplexing (TDD-OFDM) system. Both base stations, concentrated and distributed, were equipped with an array consisting of 100 antennas, and the maximum number of 20 simultaneously active users is considered. The channels are simulated using a well-tested and rigorous RT software. Using RT channel modeling, this work characterizes the up-link channels with both technologies, estimating the coherence bandwidth of the channels and analyzing the achievable capacity, assuming perfect channel state information (CSI). The results show that the D-mMIMO channel outperforms the C-mMIMO one from the point of view of their behavior in broadband as well as in terms of the obtainable capacity.

Recent standardization of portions of the millimeter-wave (mm-wave) band for fifth-generation (5G) operation has called for further research on how short-term fading behaves in that unexplored part of the spectrum. With such a target, this paper reports on a thorough measurement campaign conducted in an indoor environment characterized by rich-multipath scattering, a part of a modern building, with floor and ceiling constructed of reinforced concrete over steel plates with wood and plasterboard-paneled walls. Particularly, measurements have been performed in a variety of scenarios, under line-of-sight (LoS) and non-line-of-sight (nLoS) conditions, for a wide range of frequencies, namely from 25 to 40 GHz- a span of 15 GHz- therefore, including 26, 28 and 39 GHz. First and second order statistics of representative fading models, namely Rayleigh, Rice, Nakagami, folded normal, ${\alpha } $ - ${\mu } $ , ${\eta } $ - ${\mu }$ , ${\kappa } $ - ${\mu } $ , and ${\alpha } $ - ${\eta } $ - ${\kappa } $ - ${\mu } $ have been investigated. The metrics used in the analysis were the normalized mean square error (NMSE), the Kolmogorov-Smirnov (KS), and the Akaike information criterion (AIC). Additionally, the study of the ${\kappa } $ - ${\mu } $ model is advanced, in which new, exact, simple closed-form expressions for probability density function, cumulative distribution function, and level crossing rate are derived for some particular cases, namely for ${\mu = n+ 1/2}$ in which ${n\in {{\mathbb {N}}}}$ .

The objective of this work is to propose experimental path loss propagation models for communication channels in indoor environments. In this sense, an experimental path loss characterization has been achieved, according to the measurements campaign carried out in a typical scenario of a university campus. These narrowband measurements were collected in the laboratory environment at 3.7 GHz in line-of-sight (LOS) condition. Also, these measurements were carried out at night to simulate stationary channel conditions. Thus, the results obtained show the values of the parameters of the close-in (CI) free space reference distance and floating-intercept (FI) path loss models, in terms of the transmitter and receiver separation distance. It should be noted that these values of the path loss models have been extracted applying linear regression techniques to the measured data. Also, these values agree with the path loss exponent values presented by other researchers in similar scenarios. The path loss behavior can be described with the implementation of these models. However, more measurement campaigns are needed to improve the understanding of propagation channel features, as well as to obtain better precision in the results obtained. This, in order to optimize the deployment and performance of next fifth-generation (5G) networks that combine indoor environments to offer their services and applications.

A thorough measurement campaign in an indoor environment at the millimeter-wave band is carried out with an aim at characterizing the short-term fading channel in terms of its higher-order statistics. The measurements are conducted in a variety of scenarios, with frequencies ranging from 55 to 65 GHz, in line-of-sight and non-line-of-sight conditions, and combinations of horizontal and vertical polarizations at both the transmitter and the receiver. A number of fading models are tested, namely Rayleigh, Rice, Nakagami-m, α-μ, κ-μ, η-μ, and α-η-κ-μ. The main second-order statistics under analysis are the level crossing rate (LCR) and average fade duration (AFD) both given per distance unit. From the experimental data, the parameters of these statistics are estimated, and the corresponding curves of the theoretical models are compared with the empirical ones and the best model is selected. Additionally, the study of the very general distribution, namely α-η-κ-μ, is advanced, in which new expressions for time-/distance-domain LCR and AFD are derived using an envelope-based approach. Such an approach leads to integral-form formulations with much less computational complexity and computes rapidly compared with the already existing ones presented elsewhere, also given in the integral form. Furthermore, a series of expansion expression for the α-η-κ-μ time-/distance-domain LCR is then derived that improves even further the computational time.

Concerning the design and planning of new radio interfaces for the fifth-generation (5G) systems, this paper presents a useful contribution to the characterization of the wideband indoor radio channel in the 3-4-GHz frequency band. A measurement campaign has been carried out in two different indoor scenarios to analyze some of the most important wideband parameters of the propagation channel, including a thorough analysis of its behavior to meet the new radio technology challenges. The channel measurement setup consists of a virtual vertical uniform array at the receiver side of the link that remains at a fixed position, whereas the transmitter side, which is equipped with a single antenna, is placed at different positions in the environment under analysis. The measurement setup emulates the up-link of a multi-user multiple-input multiple-output (MIMO) system and allows obtaining the broadband parameters of the multiple channels that are established between the transmitter and each one of the antennas of the receiver array. The results and conclusions about the path loss, temporal dispersion, and coherence bandwidth are included, along with an analysis of the spatial correlation between wideband channels when one of the antennas is an array.

In this paper, a novel form of the folded normal (FN) distribution has been proposed to model the small-scale fading in wireless communications. From a multiple-input multiple-output (MIMO) measurement campaign conducted in a lab environment with the line-of-sight (LOS) conditions at both the 60 and the 94 GHz bands, the authors obtain the parameters of the Rician, FN, and k-μ distributions. These parameters have been calculated by using the least square (LS) approximation and with techniques of statistical inference. The FN distribution provides the best fitting to the experimental results using the Kolmogorov-Smirnov (K-S) test for the inferred estimators with values of the fulfillment of 100% and 69.82% at the 60 and 94 GHz bands, respectively, for a significance level of 1%.

Abstract In this paper, estimators of the Nakagami-lognormal (NL) distribution based on the method of log-moments have been derived and thoroughly analyzed. Unlike maximum likelihood (ML) estimators, the log-moment estimators of the NL distribution are obtained using straightforward equations with a unique solution. Also, their performance has been evaluated using the sample mean, confidence regions and normalized mean square error (NMSE). The NL distribution has been extensively used to model composite small-scale fading and shadowing in wireless communication channels. This distribution is of interest in scenarios where the small-scale fading and the shadowing processes cannot be easily separated such as the vehicular environment.

The design of future vehicular communication systems is receiving considerable attention from the scientific community and also from standard organizations and vehicle manufacturers due to the introduction of intelligent transportation systems (ITS). These concepts bring potential applications for improving traveling conditions in terms of road safety, aiming at reducing the number of traffic accidents as well as providing easy traffic flow. Moreover; in order to design, evaluate and optimize ITS applications oriented towards vehicular safety and based on wireless systems; knowledge of the propagation channel is vital, in particular path-loss conditions. In this context, this paper analyzes path loss in terms of transmitter (Tx) and receiver (Rx) separation distance. The analysis is based on experimental channel measurements carried out at 700 MHz and 5,9 GHz. Values for the path loss exponent and the standard deviation of shadowing are reported and compared with other results published in the literature. The measurement campaign was conducted in a suburban area characterized by high-traffic density.

The bivariate Nakagami-lognormal distribution used to model the composite fast fading and shadowing has been examined exhaustively. In particular, we have derived the joint probability density function, the cross-moments, and the correlation coefficient in power terms. Also, two procedures to generate two correlated Nakagami-lognormal random variables are described. These procedures can be used to evaluate the robustness of the sample correlation coefficient distribution in both macro- and microdiversity scenarios. It is shown that the bias and the standard deviation of this sample correlation coefficient are substantially high for large shadowing standard deviations found in wireless communication measurements, even if the number of observations is considerable.

The knowledge of the propagation channel properties is an important issue for a successful design of ultrawideband (UWB) communication systems enabling high data rates in short-range applications. From an indoor measurement campaign carried out in a typical laboratory environment, this paper analyzes the path loss and time-dispersion properties of the UWB channel. Values of the path loss exponent are derived for the direct path and for a Rake receiver structure, examining the maximum multipath diversity gain when an all Rake (ARake) receiver is used. Also, the relationship between time-dispersion parameters and path loss is investigated. The UWB channel transfer function (CTF) was measured in the frequency domain over a channel bandwidth of 7.5 GHz in accordance with the UWB frequency range (3.1–10.6 GHz).

This article explores the chronology of change in the Spanish prison system, especially during the transition from the Francoist dictatorship (1975–1982). It indicates how the incarcerated population had come to reflect Francoism's management of social change (including via an increasing use of preventive detention). By the early 1970s, political activists represented a minority of those incarcerated, although a minority that had grown steadily again from the late 1960s. The article discusses relations between the different groups of inmate, the rapidly-deteriorating conditions inside the gaols, and the emergence in the early transition period (1976) of prison protests (COPEL) led by common prisoners whose main objective was inclusion in the gaol amnesty then being proposed as part of the exit strategy from dictatorship. The article analyzes the reactive rather than proactive response to COPEL of Spain's transitional governments, composed of reformist Francoists, and the eventual outcome in a prison reform law in 1979. The article assesses the law's limited practical effect inside the gaols, because of severe budgetary restrictions combined with Spain's rising prison population – the latter mirroring developments across Western democracies generally. [ABSTRACT FROM AUTHOR]