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Large-scale propagation characterization for multiple measurements in a micro-cell scenario is carried out at 5G frequency (3.8 GHz). Distance-based path loss is computed for routes with line-of-sight, non-line-of-sight and obstructed-line-of-sight conditions, assuming a simple power law model. Path Loss exponents are computed for the whole routes, giving an effective understanding of the propagation environment. Empirical shadowing distribution is fitted to red Gaussian and non-Gaussian probability distributions. All previous propagation parameters are also found assuming measurements with similar transmitter locations come from the same channel conditions. This assumption is tested. Finally, although frequently absent in standard channel models, and useful for statistical ensemble average approximations, stationary regions are computed for all the routes. [ABSTRACT FROM AUTHOR]

A model parameterization and validation is proposed for specular-diffuse clustered channel models. The double-directional model parameters, based on an experimental measurement campaign, are presented. The specular-diffuse model is validated with regard to the following validation metrics: mutual information, singular values, Demmel condition number and ellipticity. A good agreement is observed when comparing the model with experimental measurements. Finally, the influence of the diffuse multipath component on the performance of the model validation is evaluated. [ABSTRACT FROM PUBLISHER]

Contributions from trees may represent an important part of wireless communication channels in outdoor environments. For this reason, a simple ray-based model for scattering by tree branches has been developed and implemented in a pre-existent ray-tracing tool. In addition to the new rays created by scattering, an empirical attenuation model has also been implemented. Simulations have been validated with measurements in a campus scenario where several trees where present alongside the propagation environment. Received power results show an increase in accuracy when accounting for trees. [ABSTRACT FROM PUBLISHER]

Multiple-input–multiple-output (MIMO) technologies allow high data rates to be obtained, but they suffer from interantenna correlation caused by the limits in interantenna spacing. Polarized MIMO systems resolve this problem by using colocated perpendicularly polarized antennas that have low interantenna correlation. In this paper, a polarized single-directional channel model for 2\times N MIMO systems at 3.6 GHz in an indoor environment is presented. The wireless channel is modeled as a sum of clusters, where each cluster has specular and diffuse components. The polarization of the specular component of the clusters is included by considering a per-path polarization. The diffuse component of the clusters is modeled with a Fisher–Bingham (FB5) spectrum in the azimuth–coelevation domain and with an exponential power delay profile. Polarization is analyzed by introducing the cross-polar discrimination of the exponential power delay profile parameters. All of the parameters in the model are extracted from an experimental measurement campaign performed in an indoor environment at 3.6 GHz. Individual paths are extracted from the measurements with the space-alternating generalized expectation–maximization (SAGE) algorithm. These paths are grouped in clusters within the azimuth of arrival–elevation of arrival–delay domains at the receiver side using automatic clustering algorithms. The specular component properties of the clusters are then determined. Finally, the diffuse components of the clusters are investigated and parameterized by applying a beamforming algorithm on the diffuse part of the impulse response. [ABSTRACT FROM PUBLISHER]

Multiple-input-multiple-output (MIMO) wireless channel models are often too simplistic to accurately model wireless propagation effects or too complex and/or site specific to be used for analytical purposes. In this paper, we develop a double-directional MIMO channel model that accounts for important propagation effects like scattering, clustering, and channel depolarization and antenna effects like antenna diversity, cross polarization, and random array orientation, while still retaining an intuitive representation. The proposed model can be parameterized using channel measurements obtained from site-specific measurement campaigns or from standard-based channel models. We show, using simulations, that the proposed model captures channel and antenna effects not included in other models, like the third-generation partnership program (3GPP) spatial channel model, the WINNER, and the IEEE 802.11n channel model. We use the model to study the impact of random orientation and channel depolarization on the data rates of a MIMO system. [ABSTRACT FROM AUTHOR]

We propose and parameterize an empirical model of the outdoor-to-indoor and indoor-to-indoor distributed (cooperative) radio channel, using experimental data in the 2.4-GHz band. In addition to the well-known physical effects of path loss, shadowing, and fading, we include several new aspects in our model that are specific to multiuser distributed channels: 1) correlated shadowing between different point-to-point links, which has a strong impact on cooperative system performance; 2) different types of indoor node mobility with respect to the transmitter and/or receiver nodes, implying a distinction between static and dynamic shadowing motivated by the measurement data; and 3) a small-scale fading distribution that captures more severe fading than that given by the Rayleigh distribution. [ABSTRACT FROM AUTHOR]

Body area networks consist of a number of biological sensors communicating over the air with a central sink placed in close proximity of the human body. A promising solution is to use multisens- or multiantenna ultrawideband architecture; each sensor carries one antenna, while the central sink supports an antenna array. In this paper, a complete analytical channel model has been developed for the on-body diffracted waves mechanism. It builds on the existing IEEE 802.15.4a standard channel model and offers an innovative space-time correlation model. [ABSTRACT FROM AUTHOR]

This paper describes the results achieved by an experimental campaign whose goal was to characterize the directional propagation channel at 1.9 GHz in forested areas for moderate antenna heights. These experimental results are useful in the context of pedestrian radio-localization systems relying on cellphone signals. Wideband experimental results, which are recorded with transmit-to-receive distances ranging from 40 to 110 m, indicate that the path loss is well modeled by ITU-R Recommendation 833-4. The temporal fading and multipath dispersion are also analyzed. The delay spread, which ranges from 60 to 120 ns, is strongly anticorrelated with the temporal coherence and increases with transmit-to-receive distance. The azimuth spread remains limited, with average values of about 15°. [ABSTRACT FROM AUTHOR]

MIMO technologies enable high communication data rates, but suffer from the large antenna spacing that is required to achieve sufficiently low inter-antenna correlation. Cross-polarized antenna systems resolve this problem by using perpendicular antennas. Correlation is reduced while keeping antennas co-located. Inter-antenna correlation and cross-polar discrimination (XPD) are two fundamental parameters of these polarized antenna systems. This paper proposes an analytical channel model, from which closed-form solutions for the correlation coefficient and the XPD are deduced. The environment is supposed to have a truncated Laplacian power azimuth spectrum that is widely used in standardization bodies. The receiving di- or tri-pole antenna can have random orientation. The correlation and the XPD show to be highly sensitive to receiver orientation, azimuth spread and environment depolarization behavior. Measurements have been conducted at 3.5 GHz to validate the solution obtained. Good agreement is achieved when comparing theoretical curves and experimental results for different receiver orientations, both for the correlation coefficient and the XPD. [ABSTRACT FROM AUTHOR]

Space-time code (STC) designs commonly rely on the assumptions of independent and identically distributed (i.i.d.) Rayleigh channels (being either slow or fast fading) and high signal-to-noise ratio (SNR). However, it has been shown that poor scattering conditions can have detrimental effects on the performance of STCs and that the behavior of codes at high SNR is radically different from the finite SNR behavior. This calls for new design criteria that correctly predict the behavior of codes in correlated channels at finite SNR. In this paper, we investigate how spatially and temporally correlated Ricean fading affects the performance of STCs at finite SNR. We derive a code design criterion leading to robust STCs in a wide variety of propagation conditions and do not require any channel knowledge at the transmitter. Codes satisfying this criterion are shown to perform sensibly better in correlated channels than codes designed only for i.i.d. slow or fast Rayleigh-fading channels. Examples of space-time trellis codes and algebraic codes are proposed in order to illustrate the developed criterion. [ABSTRACT FROM AUTHOR]

The performance analysis and the subsequent design of space-time codes (STC) in multiantenna channels commonly assume an infinite signal-to-noise ratio (SNR). This assumption has been shown to be justified in uncorrelated Rayleigh-fading channels. By contrast, this correspondence investigates STC in all SNR regimes and in the broad class of space-time correlated Ricean fading multiple-input-multiple-output (MIMO) channels. For rank-deficient codes, it is proven analytically that the error probability is significantly affected by spatial correlations and coherent components, irrespective of the SNR range and the temporal correlation. For full-rank codes, the performance and the code design are shown to be affected by spatial correlations and/or coherent paths only at finite SNE in slow fading channels, whereas in time-varying channels, they are affected in all SNR regimes. Hence, there is no guarantee that STC designed for independent and indentically distributed (i.i.d.) Rayleigh-fading channels perform adequately in space-time correlated Rayleigh/Ricean channels. Simulation examples confirm the conclusions drawn from the analytical derivations. They further illustrate that the use of a high SNR assumption does not allow to accurately estimate the behavior of STC in practical scenarios and should, thus, be used with care. [ABSTRACT FROM AUTHOR]

This paper presents a stochastic geometry-based model of the multiple-input-multiple-output channel, as seen by the user terminal based on the extraction of cluster parameters from wideband data measured at 1.9 GHz in short-range outdoor macrocellular environments. Clusters are first identified through data visual inspection. Then, a statistical characterization is carried out based on a delay-oriented classification of the clusters. Extraction results show that at each location, six to eight clusters are present, with average cluster delay and azimuth root mean square spreads of about 10-15 ns and 10°-20°, respectively. A cluster-oriented geometry-based model is then developed and validated with measurement results, including spatial correlations for broadside and inline receive antenna configurations. [ABSTRACT FROM AUTHOR]

Space-time code (STC) designs classically rely on the assumption of independent and identically distributed (i.i.d.) Rayleigh channels. However, poor scattering conditions may have detrimental effects on the performance of STCs. In this letter, we derive code-design criteria leading to robust STCs in a large variety of slow-fading propagation conditions. No channel knowledge is assumed at the transmitter. Codes satisfying these criteria are shown to perform much better on real-world channels than codes designed only for i.i.d. channels. As examples, the robustness of various spatial multiplexing schemes, linear dispersion codes, and space-time trellis codes is discussed based on those criteria. [ABSTRACT FROM AUTHOR]

The wireless channel for nomadic diversity-based wireless networks operating at 1.9 GHz is characterized. Using a 1 times 2 wideband measurement chain, four typical indoor office and industrial environments have been investigated: a corridor, an office room, a laboratory room and a large industrial hall. The measurement equipment is constituted by an 80-MHz transmitter. At the receiver, two omnidirectional antennas are connected to a wideband channel sounder through a switch, in order to measure an estimate of the instantaneous vector channel. Special attention is given to the experimental procedure itself, so as to take into account the specificity of nomadic systems (as opposed to usual mobile systems). The measurement analysis reveals that the shadowing, Rician K-factor and delay-spread are lognormally distributed. A path-loss model is derived, and cross-correlations between K-factor, delay-spread and shadowing are analyzed. The channel correlations at the user terminal or at the access point are also derived, and related to the individual channel characteristics [ABSTRACT FROM PUBLISHER]

This paper investigates the mutual information of several 2 x 2 systems using orthogonal polarizations. Analytical approximations of the mutual information in equi-power allocation scenarios are derived and compared in both Rayleigh and Ricean fading conditions. [ABSTRACT FROM AUTHOR]

This paper proposes various metrics to characterize space-time focusing resulting from application of time reversal techniques in richly scattering media. The concept and goals of time reversal are presented. Pertinent metrics describing both the time and space focusing effects are outlined. Two examples based on a model of discrete and continuous scattering media are used to illustrate how the proposed metrics vary as a function of various system and channel parameters, such as the bandwidth, delay and angle spreads, number of antennas, etc. [ABSTRACT FROM AUTHOR]

This paper aims at characterizing the spatial wireless channel at 1.9 GHz, based on a 1 × 2 measurement chain. A typical campus/residential area and an industrial area have been investigated. The measurement equipment is constituted by an 80-MHz transmitter at 1.9 GHz, located at the top of a building. At the receiver, two omnidirectional antennas are connected to a wide-band channel sounder through a switch in order to measure an estimate of the instantaneous vector channel. It is found that the Ricean K-factor and the delay spread are lognonnally distributed, while the azimuth spread at the receive side follows a Gaussian distribution. The range dependence of various parameters are pointed out and compared with empirical models. The impacts of antenna spacing and array orientation on the channel correlation are high- lighted and compared to theoretical simulation results. Finally, the cross-correlation properties between K-factor, delay spread, azimuth spread, and channel correlation are analyzed. [ABSTRACT FROM AUTHOR]

This paper addresses the extension of a stochastic geometry-based scattering model to multipolarized transmissions. The initial approach is based on a geometrical distribution of obstacles derived from known power-delay profiles. Each scattering process is statistically described by a matrix reflection coefficient corresponding to dual-polarization states. Ultimately, the model allows us to simulate the effects of the range on K-factor, delay-spread, Doppler spectrum, channel correlations and capacity, branch power ratio, and cross-polar discrimination. Simulation results are compared with existing measurements at 2.5 GHz. The proposed model is then used to investigate various dual-polarization 2 × 2 multiple-input-multiple-output (MIMO) schemes such as 0°/90° or ±45°, as well as to optimize the design of multipolarized MIMO schemes. [ABSTRACT FROM AUTHOR]

Describes a deterministic three-dimensional electromagnetic model which allows simulation of the radiowave propagation for microcellular wise-band communication systems in urban areas. Function of third-generation mobile systems; Modeling limitations that could explain the discrepancies in the amplitudes.

Describes a physically based stochastic approach that allows to predict the narrowband fading statistics for macro- and megacellular channels operating in urban areas. Outline of the modeling philosophy; Comparison of the model with L-band experimental data; Predictions of signal-level statistics.

Discusses specific mobile satellite urban configurations such as a long straight street lined on both sides by buildings and a crossroad in relation to complete statistical models for land mobile satellite systems in urban areas. Ray-tracing tool; Description of canonical scenarios and environments considered; Comparison between a long street and a crossroad.

Proposes a shadowing correlation model in the context of a physical-statistical approach in the view of satellite diversity in the built-up areas. Description of the shadowing correlation model; Shadowing correlation coefficient for several pairs of communication satellites with different elevation angles; Application of the model to low-earth orbit systems.

In this article, we analyze the characteristics of indoor radio channels at millimeter waves. Measurements were performed using a large virtual antenna array (VAA), for massive multiple input multiple output (MIMO) applications. The results in terms of correlation and multipath components (MPCs) characteristics are analyzed for the whole large array and virtual subarrays composing it. Common MPC among the subarrays are identified, and the impact on the overall channel large-scale parameters is discussed. [ABSTRACT FROM AUTHOR]

A plane-wave spectrum method is presented for the fast computation of radiation integrals for source and observation plates, which can be arbitrarily tilted and separated by an intermediate-to-far-field distance. The method expedites the direct and inverse transforms between spatial and spectral domains using unequally spaced fast Laplace transforms. These fast algorithms allow one to combine fast Fourier transforms (FFTs) and contour deformation in the complex plane with controllable accuracy and computation times close to that of a single 2-D FFT. Hence, scattering interactions between plates of sizes up to thousands of wavelengths can now be computed within seconds using current desktop computers. The fast method is validated here for the case of radio propagation in a canyon street modeled with electrically large facets using the physical optics approximation. [ABSTRACT FROM AUTHOR]

With the deep integration between the unmanned aerial vehicle (UAV) and wireless communication, UAV-based air-to-ground (AG) propagation channels need more detailed descriptions and accurate models. In this paper, we aim to conduct cluster-based characterization and modeling for AG channels. To our best knowledge, this is the first study that concentrates on the clustering and tracking of multipath components (MPCs) for time-varying AG channels. Based on measurement data at 6.5 GHz with a bandwidth of 500 MHz, we first estimate potential MPCs utilizing the space-alternating generalized expectation-maximization (SAGE) algorithm. Then, we cluster the extracted MPCs by employing K-Power-Means (KPM) algorithm under multipath component distance (MCD) measure. For characterizing time-variant clusters, we exploit a clustering-based tracking (CBT) method, which efficiently quantifies the survival lengths of clusters. Ultimately, we establish a cluster-based channel model, and validations illustrate the accuracy of the proposed model. This work not only promotes a better understanding of AG propagation channels but also provides a general cluster-based AG channel model with certain extensibility. [ABSTRACT FROM AUTHOR]

The era of wireless communications began at the turn of the 20th century, when Guglielmo Marconi used electromagnetic waves to transmit telegraph signals from ships to stations onshore. To understand how radio signals propagate is critical for wireless communication system design. With the development of wireless communications, much effort has been made to characterize radio propagation in different frequency bands and physical environments. Radio propagation and wireless channel modeling are essential for communication system simulation, channel emulator design, wireless system planning and optimization, and the development of regulations and standards in wireless communications ,. [ABSTRACT FROM AUTHOR]

This paper investigates so-called diagonally correlated multiple input-multiple output (MIMO) channels, which provide higher ergodic capacity than independent and identically distributed (i.i.d.) fading channels. The presented analysis details physical scenarios leading to such channels, some properties of the channel matrix, and an analytical expression for its ergodic capacity. [ABSTRACT FROM AUTHOR]

Ray tracing is a powerful tool to obtain deterministic and dynamic descriptions of communication channels. However, performing ray tracing simulations at each discrete time instant is computationally expensive. Instead, a new approach is proposed to extrapolate results obtained from a single ray tracing simulation. It relies on the geometric tracking of interaction points (i.e. reflection or diffraction points), enabling analytical or numerical predictions of the evolution of any ray identified during an initial ray tracing simulation. The performance of this new approach is studied on several canonical vehicle-to-vehicle configurations, as part of a statistical study. Focus is also given to the time horizon during which dynamic ray tracing is possible, related to the lifetime of the main rays. This time horizon can be directly estimated based on the knowledge of the geometry and its evolution. It is found to be the main parameter influencing the accuracy and the computational gain of the presented approach. [ABSTRACT FROM AUTHOR]

The classical physical optics (PO) formulation of the scattered fields suffers from the loss of accuracy when the observation angle widely deviates from the specular direction. This is even worse in the “forward region,” i.e., for the bistatic angles between 90° and 270°. The method presented in this article aims at improving the accuracy of the fields in this region by finding the currents induced on the nonilluminated part of the object, where the classical PO assumes zero currents. The proposed approach reformulates the initial problem using equivalent currents over a domain surrounding the object. The equivalent currents then act as new sources that induce electrical currents computed by the classical PO formulation. The computation of the equivalent problem is accelerated using the multipole expansion of Green’s function, including appropriate singularity extraction in the very near field. This approach provides an error that is significantly lower in the forward direction than the classical PO formulation. The principles of this new approach are presented and validated for the 2-D scenarios. [ABSTRACT FROM AUTHOR]

This article presents a vehicle-to-pedestrian (V2P) channel model based on an extensive measurement campaign carried out at 3.8 GHz. Several propagation conditions were investigated and different mobility patterns were measured. A stochastic channel modeling approach is proposed and parametrized. The model consists of two components, i.e. the first path component and the secondary multi-path components (MPCs). These components were detected via a detection and tracking algorithms presented here. It was found that the time variant contributions of each detected path can be modeled as a combination of path loss (PL), large- and small-scale fading. [ABSTRACT FROM AUTHOR]

Inhomogeneous plane waves (IPWs) based on a linear contour deformation provide an accurate and concise field representation for scattering problems in which source and observation domains are visible within a limited angular sector. Given an error level, we derive closed-form expressions for the truncation limit, the sampling step, and the contour slope that minimize the number of plane waves. A relation is drawn between the required number of plane waves and the degrees of freedom of the field, defined as the minimum number of orthonormal basis functions that represents scattered fields. The sampling rules are then applied to an efficient evaluation of the physical optics radiation integral. [ABSTRACT FROM AUTHOR]

Diffuse scattering (DS), mostly caused by macroscopically rough surfaces, can be modeled by an effective roughness (ER) approach. In the ER approach, the object surface is divided into tiles, and the DS field amplitude associated with each tile is given. Assuming that the transmit antenna (or emitted field) is fixed and the phases associated with different tiles are independent, this paper proposes a phase evolution model based on the relative spatial locations of the receive antenna (Rx) to each tile. The proposed model contains two parts: the deterministic part that depends on the variation of the distance from Rx to tile center, and the correlated random part that depends on the variation of the angle between the Rx and the normal vector of tile. The correlation of the tile field phases resulting from the angular variation is modeled by the exponentially damped cosine correlation function. The proposed phase evolution model is evaluated by being applied to the ER approach to predict the DS component of radio channel transfer function (CTF). The predicted DS-CTF is compared with the reference (simulated data by physical optics and measured data in well-controlled environment) in terms of the spatial autocorrelation as well as the spatial Doppler spectrum. [ABSTRACT FROM PUBLISHER]

In this paper, we have investigated the effects of vehicular traffic on interpersonal wearable-to-wearable (W2W) communications channels in an urban environment at 2.45 GHz. In particular, we have studied the perturbations in the received signal caused by different types of vehicles as they passed through a channel between two persons who maintained various relative orientations while positioned at the opposite sides of a road. As the channel underwent different fading mechanisms depending on whether the vehicle was approaching, transitioning (i.e., intersecting the direct signal path), or receding from the persons, the overall disturbance was appropriately segmented depending on the journey stage. The results have shown that relative body orientation was a significant factor when considering the impact that a vehicle can have on a W2W link. When both persons faced the oncoming traffic, the link was particularly susceptible to significant fading events with variations in the received signal power from the unperturbed state as great as 44.1 dB observed to occur. For all of the journey stages, irrespective of the relative orientation of the persons, the logarithmically transformed long-term fading process was found to be multimodal and well described by a Gaussian mixture model. During the transitioning phase, shadowing caused by the passing automobile obstructing the line-of-sight signal path was found to be the main contributor to the signal fading. However, probably the most remarkable result of the channel characterization work conducted in this paper was the severity of the short-term fading often observed. Such was the intensity of the measured envelope fluctuation in many of the scenarios, we have been able to utilize the recently proposed $\kappa -\mu $ extreme distribution with great success and in the process, provide a further important empirical validation of this new fading model. Moreover, we have used the resistor-average distance, which is derived from the Kullback–Leibler distance to show the improved fit that the $\kappa -\mu $ extreme distribution offers compared with the $\kappa -\mu $ distribution when used to model the W2W channel in this fading environment. [ABSTRACT FROM PUBLISHER]

To provide higher data rates, as well as better coverage, cost efficiency, security, adaptability, and scalability, the 5G and beyond 5G networks are developed with various artificial intelligence (AI) techniques. In this two-part article, we investigate the application of AI and, in particular, machine learning (ML) to the study of wireless propagation channels. It first provides a comprehensive overview of ML for channel characterization and ML-based antenna–channel optimization in this first part, and then, it gives a state-of-the-art literature review of channel scenario identification and channel modeling in Part II. Fundamental results and key concepts of ML for communication networks are presented, and widely used ML methods for channel data processing, propagation channel estimation, and characterization are analyzed and compared. A discussion of challenges and future research directions for ML-enabled next-generation networks of the topics covered in this part rounds off this article. [ABSTRACT FROM AUTHOR]

This two-part paper investigates the application of artificial intelligence (AI) and, in particular, machine learning (ML) to the study of wireless propagation channels. In Part I of this article, we introduced AI and ML and provided a comprehensive survey on ML-enabled channel characterization and antenna-channel optimization, and in this part (Part II), we review the state-of-the-art literature on scenario identification and channel modeling here. In particular, the key ideas of ML for scenario identification and channel modeling/prediction are presented, and the widely used ML methods for propagation scenario identification and channel modeling and prediction are analyzed and compared. Based on the state of the art, the future challenges of AI-/ML-based channel data processing techniques are given as well. [ABSTRACT FROM AUTHOR]

System design and deployment of millimeter-wave (mmWave) wireless communication systems for outdoor coverage need sophisticated channel models to describe the wave interaction with illuminated physical objects. However, the conventional physical–statistical model cannot accurately predict the site-specific mmWave channel characteristics when involving complex system configurations and geometric information of transceiver relative locations. A framework of machine learning (ML) assisted channel modeling approach is proposed, in which the statistical models are leveraged for inter-cluster-level channel characterization and the propagation properties within each kind of clusters are predicted using a hybrid physics-based and data-driven approach. In particular, with a focus on the mmWave through-vegetation-scattering effect, a set of dedicated directional channel measurements and ray-tracing simulations is performed in an identical vegetated street canyon environment at 28 GHz for the performance evaluation of the proposed approach. Moreover, the training results and model validation in different environments show that comparing with the physical–statistical model, the proposed hybrid model, which adds the environment features to the artificial neural network (ANN) as inputs, has higher prediction accuracy and greater generalization ability in terms of the site-specific through-vegetation cluster parameters, such as vegetation attenuation, delay spread (DS), and angular spread. [ABSTRACT FROM AUTHOR]

Investigation of small-scale fading in indoor peer-to-peer networks based on radio channel measurements shows that Rayleigh or double Rayleigh (DR) fading with or without line-of-sight (LOS) component can occur, depending on the mobility and on the scattering properties of the environment. While in double-mobile scenarios, the predominant fading mechanism is a combination of Rayleigh and DR fading, Rician fading and fading events caused by the combination of a constant term with a DR component are also occasionally observed. In single-mobile scenarios, temporal fading is Rician or Rayleigh distributed. Additionally, measurements reveal that fading statistics evolve significantly over time, even for small-scale motions of the nodes. We model the transitions between the fading states by means of a hidden Markov model, parameterized from our measurements. Eventually, we propose a complete simulation model that generates channel realizations by combining measurement-based first-order statistics with geometry-based second-order statistics for both types of node mobility. [ABSTRACT FROM PUBLISHER]

This paper investigates the prediction capabilities of a Ray-Tracing tool with advanced features, i.e., diffuse scattering and penetration, in terms of the angular spreads and spectra of the directional propagation channel. In particular, it highlights the angular behavior of dense multipaths, which may represent a non-negligible part of the received power, by comparing Ray-Tracing simulations with experimental data (office and laboratory environments). Results show that a Ray-Tracing approach including diffuse scattering is able to reproduce the dense multipath angular spreads, with errors around 4 to 20 degrees, and that scattering from ceiling is significant to predict the elevation spread. The assumption that diffuse scattering is clustered and strongly related to the most significant specular components is also successfully validated. [ABSTRACT FROM PUBLISHER]

In this article, a beam-shaping technology, based on arrays of parasitic elements, is presented for the modulation of radiation patterns of existing 4G or 5G base station antennas. First, based on the cell's geographic topology and the requirements of different radiation power exposure, and using ray-tracing simulation, the desired antenna radiation patterns are determined and represented with spherical harmonics. Those patterns are implemented in a prototype in the 1800 MHz band using parasitic radiators, loaded with different impedances, to be placed in front of the existing cellular base station antenna. A smaller prototype demonstrates the electronic control of parasitic loads using varactor diodes. The developed prototypes have been tested in the laboratory and the measurements are in a good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

As wireless connectivity becomes increasingly ubiquitous, a greater emphasis will be placed upon the seamless integration of dissimilar networking technologies. One such example of this will occur in urban environments, where wearable devices and vehicular networks will operate in close proximity to one another. Clearly, a natural extension to both types of network is their interconnectivity through vehicle-to-pedestrian (V2P) or equivalently pedestrian-to-vehicle (P2V) communications as part of a much greater vehicle-to-X (V2X)-based intelligent transportation system. To this end, we empirically investigate the P2V communications channel at 5.8 GHz for the case of a moving vehicle when a person positioned by the edge of a road was either stationary or walking parallel to the side of the highway. The measurements considered a chest-mounted transmitter and four receiver locations on the vehicle covering the front wing mirrors and two positions on the roof, which simultaneously recorded the received signal power. To characterize the propagation mechanisms which are responsible for shaping the received signal in the P2V channel, we decomposed it into its path loss (PL), large-scale, and small-scale fading components. We first show that although there was evidence of interference caused by multiple rays interacting with one another, the popular two-ray ground-reflection PL model was unable to adequately describe the compounded effects of the vehicle and pedestrian’s body on the signal attenuation in the majority of the considered scenarios. Instead, we found that the overall PL was well characterized using a dual-slope log-distance model, with lognormal large-scale fading. Due to the often severe small-scale fading that was observed in the P2V channel, we have been able to utilize the $\kappa $ - $\mu $ extreme distribution with considerable success to characterize the worse than Rayleigh fading conditions which were encountered. [ABSTRACT FROM AUTHOR]

Radio channel modeling has been an important research topic, since the performance of any communication system depends on channel characteristics. So far, most existing clustering algorithms are conducted based on the multipath components (MPCs) extracted by using a high-resolution parameter estimation approach, e.g., SAGE or MUSIC, etc. However, most of the estimation approaches require prior information to extract MPCs. Moreover, the high-resolution estimation approaches usually result in relatively high complexity, and thus, the clusters can only be identified by using an offline approach after the measurements. Therefore, a power-angle-spectrum (PAS) based clustering and tracking algorithm (PASCT) is proposed in this paper. First, a PAS is extracted from measurement data by using a Bartlett beamformer. For each PAS, the potential targets are selected from the background and separated into clusters by using image processing approaches. The recognized clusters are characterized by the following three attributes: size, position, and shape feature, where an orientation histogram is developed to describe the shape feature of the clusters. Moreover, a cost minimizing tracking approach based on Kuhn–Munkres method is proposed to accurately identify the clusters in non-stationary channels. The proposed PASCT algorithm is validated based on both simulations and measurements. It is found that the dominating clusters in both line-of-sight and non-line-of-sight environments can be well recognized and tracked with the proposed algorithm. By using the proposed algorithm, the dynamic changes of the clusters in real-time channel measurements, e.g., number, birth–death process, and size of the clusters, can be well observed. Through the experiments, the proposed algorithm can achieve fairly good accuracy on the cluster identification with lower complexity compared to the conventional solution. [ABSTRACT FROM AUTHOR]

This paper proposes a hybrid modeling approach for the prediction of the room-to-room radio propagation channel. The model combines ray tracing (RT) with the propagation graph (PG). The PG vertices are obtained at each room by RT with the assumption that the receive antenna (or transmit antenna) virtually locates on the surface of the separating wall between the two rooms. Rays transmitted from one room to the other through the separating wall are deterministically calculated by Snell’s law of refraction. Predictions by the proposed model are compared with the measurement data from an office-to-office scenario. The results show that the proposed modeling works with the simplest parameter settings, i.e., assuming no propagation from the room containing receive antenna to the room containing transmit antenna, RT applied separately in each room only involves mechanism of line of sight and first-order specular reflection. [ABSTRACT FROM AUTHOR]

A novel localization framework is presented based on ultra-wideband (UWB) channel sounding, employing a triangulation method using the geometrical properties of propagation paths, such as time delay of arrival, angle of departure, angle of arrival, and their estimated variances. In order to extract these parameters from the UWB sounding data, an extension to the high-resolution RiMAX algorithm was developed, facilitating the analysis of these frequency-dependent multipath parameters. This framework was then tested by performing indoor measurements with a vector network analyzer and virtual antenna arrays.The estimated means and variances of these geometrical parameters were utilized to generate multiple sample sets of input values for our localization framework. Next to that, we consider the existence of multiple possible target locations, which were subsequently clustered using a Kim–Parks algorithm, resulting in a more robust estimation of each target node. Measurements reveal that our newly proposed technique achieves an average accuracy of 0.26, 0.28, and 0.90 m in line-of-sight (LoS), obstructed-LoS, and non-LoS scenarios, respectively, and this with only one single beacon node. Moreover, utilizing the estimated variances of the multipath parameters proved to enhance the location estimation significantly compared to only utilizing their estimated mean values. [ABSTRACT FROM PUBLISHER]

In this study, the authors present a measurement-based analysis of the indoor radio channel characteristics of both the specular and dense multipath components [specular part of the channel (SMC) and diffuse part of the channel] at 94 GHz within a 3 GHz bandwidth. On the basis of an investigation of the frequency stationarity of this band, they have selected multiple sub-bands to perform their evaluation. A method is developed that allowed for the estimation of the specular propagation paths, after which the remainder is regarded as the diffuse spectrum. Radio channel characteristics such as the path loss, root-meansquare delay spread, and the SMC ratio have been calculated as a function of transmitter-receiver distance, and in the different sub-bands. On the basis of the diffuse spectrum, the behaviour of the reverberation time is analysed for the first time in the 94 GHz band. [ABSTRACT FROM AUTHOR]

Vehicle-to-vehicle (V2V)-communication-based collision avoidance systems detect if two vehicles are on a collision course (e.g., in crossroads, intersections, and highway merging), and they are particularly useful in the absence of line of sight (LOS) owing to buildings, roadside infrastructures, and road bending. Relying on radio measurements using a 4 $\times$ 30 multiple-input–multiple-output (MIMO) system at 5.3 GHz, this paper presents the results of an empirical study of V2V propagation channels in two suburban crossroad scenarios, where vehicles are either moving in the same direction and separate from each other along different roads or pass each other in opposite directions at the crossing. The quasi-stationarity interval is first characterized using correlation matrix distance (CMD). Small-scale fading follows a Nakagami distribution based on the Akaike information criteria (AIC). Delay and angular dispersions are found to be significantly affected by the type of crossroad and the presence of an LOS. Cross-correlation coefficients between delay dispersion, angular dispersion, and small-scale fading behavior are also evaluated. By comparing the results of the different crossroads, it is found that the delay and angular dispersions are large in the first type of crossroad. By contrast, in the second type of crossroad, small delay and angular dispersions are observed due to road bending and obstruction by roadside trees. [ABSTRACT FROM AUTHOR]

Reliable, high-data rate indoor communication is essential to transfer crucial information between firefighters for improving their safety and decreasing the number of casualties caused by indoor fires. Since electronic monitoring systems, including antennas implemented inside the firefighter jacket, should provide high data rates, communication over a wideband channel is required. We study an 80-MHz-wide body-to-body channel at 3.6 GHz between two firefighters of a Rapid Intervention Team (RIT) performing the primary search for victims, by static and dynamic channel sounder measurements. Two ultra-wideband (UWB) substrate integrated waveguide (SIW) cavity-backed slot textile antennas were unobtrusively deployed in the front and the back sections of the firefighters’ jackets, providing up to $2\times 2$ MIMO communication. We calculate the achievable single-input single-output (SISO)-, single-input multiple-output (SIMO)-, multiple-input single-output (MISO)-, and multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM) capacities for realistic indoor broadband body-to-body communication channels between two firefighters. Furthermore, we analyze implementations of one-dimensional (1-D) spatial waterfilling and two-dimensional (2-D) space-frequency waterfilling, studying their ability to further enhance transmission of live sensor data, pictures or videos between mobile firefighters. [ABSTRACT FROM PUBLISHER]

An analysis of delay-Doppler characteristics in the presence of moving people is presented for short-range communication in an indoor environment. Channel-sounding measurements have been carried out at 3.6 GHz in a crowded university hall during several short and long breaks in-between courses. During three consecutive days, the measurements were repeated with different positions for the transmit and receive antennas. In this study, the behavior of the maximum Doppler shift and the Doppler spread was analyzed in the time-delay domain as a function of the occupation of the hall, the polarizations of the $2\times 2$ MIMO antennas, and their positions in the hall. The measurements reveal a clear distinction between the Doppler spread of the short and long breaks in the campaign, indicating a distinctive power distribution of their Doppler spectra. In addition, there is a significant contrast between the Doppler characteristics of the co- and cross-polarizations. Measurements at several positions reveal the importance of characterizing multipaths and show that the Doppler effect depends on the position of the antennas in the environment. In addition, this work also shows that the Doppler spectrum can be accurately modeled by a Cauchy distribution, allowing for the generation of parameters to describe Doppler characteristics. [ABSTRACT FROM AUTHOR]

Vehicle-to-vehicle (V2V) communications have received a lot of attention due to their numerous applications in traffic safety. The design, testing, and improvement of the V2V system hinge critically on the understanding of the propagation channels. An important feature of the V2V channel is the time variance. To statistically model the time-variant V2V channels, a dynamic wideband directional channel model is proposed in this paper, based on measurements conducted at 5.3 GHz in suburban, urban, and underground parking environments. The model incorporates both angular and delay domain properties and the dynamic evolution of multipath components (MPCs). The correlation matrix distance is used to determine the size of local wide-sense stationary (WSS) region. Within each WSS time window, MPCs are extracted using the Bartlett beamformer. A multipath distance-based tracking algorithm is used to identify the “birth” and “death” of such paths over different stationarity regions, and the lifetime of MPC is modeled with a truncated Gaussian distribution. Distributions for the number of multipaths and their positions are statistically modeled. Within each path lifetime, the initial power is found to depend on the excess delay, and a linear polynomial function is used to model the variations within the lifetime. In addition, a Nakagami distribution is suggested to describe the fading behavior. Finally, the model implementation is validated by comparison of second-order statistics between measurements and simulations. [ABSTRACT FROM PUBLISHER]

In the design of diversity and fast handover schemes for high-speed railways (HSRs), a better understanding of the shadow fading correlation properties is required. In this paper, both auto- and cross-correlation models of shadow fading in HSR environments are proposed based on a large set of measurements with 6146 cells in China. The measurements are conducted using a practically deployed and operative Global System for Mobile Communications-Railway (GSM-R) system at 930 MHz to reflect the real conditions of shadow fading in HSR environments. Seven typical HSR environments and the realistic base station (BS) parameters are considered in the analysis. It is found that the decorrelation distance is correlated with the standard deviation (STD) of shadow fading and is generally larger than 100 m in most HSR environments. The cross correlation of shadow fading between two neighboring BSs depends on the BS height and the tilt angle of the antenna, and a heuristic truncated Gaussian distribution model of cross correlation is proposed. The model is validated by the measurements conducted in another operative HSR line. The results can be used to exploit the simulation algorithms to analyze the signal-to-interference-ratio (SIR) properties and to develop new and better handover schemes for HSRs. [ABSTRACT FROM PUBLISHER]