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Vehicular Visible Light Communication (VVLC) is preferred as a vehicle to everything (V2X) communications scheme due to its highly secure, low complexity and radio frequency (RF) interference free characteristics, exploiting the line of sight (LoS) propagation of visible light and usage of already existing vehicle light emitting diodes (LEDs). Current VVLC channel models based on deterministic and stochastic methods provide limited accuracy for path loss prediction since deterministic methods heavily depend on site-specific geometry and stochastic models average out the model parameters without considering environmental effects. Moreover, there exists no wireless channel model that can be adopted for channel frequency response (CFR) prediction. In this paper, we propose a novel framework for the machine learning (ML) based channel modeling of the VVLC with the goal of improving the model accuracy for path loss and building the CFR model through the consideration of multiple input variables related to vehicle mobility and environmental effects. The proposed framework incorporates multiple measurable input variables, e.g., distance, ambient light, receiver inclination angle, and optical turbulence, with the exploitation of feed forward neural network based multilayer perceptron neural network (MLP-NN), radial basis function neural network (RBF-NN) and decision tree based Random Forest learning methods. The framework also includes data pre-processing step, with synthetic minority over sampling technique (SMOTE) data balancing, and hyper-parameter tuning based on iterative grid search, to further improve the accuracy. The accuracy of the proposed ML based channel modeling is demonstrated on the real world VVLC vehicle-to-vehicle (V2V) communication channel data. The proposed MLP-NN, RBF-NN and Random Forest based channel models generate highly accurate path loss predictions with 3.53 dB, 3.81 dB, 3.95 dB root mean square error (RMSE), whereas the best performing stochastic model based on two-term exponential fitting provides prediction accuracy of 7 dB RMSE. Moreover, MLP-NN and RBF-NN models are demonstrated to predict VVLC CFR with 3.78 dB and 3.60 dB RMSE, respectively. [ABSTRACT FROM AUTHOR]

Physics-based wireless propagation modeling and network protocol design have evolved over decades as orthogonal areas in communication systems research. This fragmented approach does not exploit available efficiencies when planning and deploying communication systems. In an attempt to integrate the two areas, we harness the understanding of the underlying physics of electromagnetic propagation to enhance the robustness of network protocol design by deriving physics-based network-level performance metrics. We use ray-tracing and parabolic equation models of 2.4 GHz propagation along tunnel and open-air sections of London Underground to evaluate the performance of a communications-based train control system. For comparison, we consider existing path loss models for tunnel environments and investigate whether they can provide sufficient accuracy to be used for network protocol design. We show that physics-based models lead to reliable predictions at the network level, similar in fidelity to using measured data and unlike using simplified channel models of the path loss exponent type. [ABSTRACT FROM AUTHOR]

Wireless communications are expected to take place in increasingly complicated scenarios, such as dense urban, forest, tunnel, and other cluttered environments. A key emerging challenge is to understand the physics and characteristics of wave propagation in these environments, which is critical for the analysis, design, and application of advanced mobile and wireless communication systems. In this paper, we present a full-wave field-based computational methodology for radio wave propagation in complex urban environments. Both transmitting/receiving antennas and propagation environments are modeled by first-principles calculations. A system-level, large scene analysis is enabled by the scalable, ultraparallel algorithms on the emerging high-performance computing platforms. The proposed computational framework is verified and validated with semianalytical models and representative measurements. [ABSTRACT FROM AUTHOR]

Wireless communications or navigation is heavily influenced by electromagnetic wave propagation. The power-delay profile (PDP) characterizes the propagation channel by simple statistics. In this communication, we propose a channel model to simulate a given wideband averaged PDP obtained by measurements or theoretical considerations, enabling to test, develop, and design radio links. The channel model is based on a geometrical stochastic approach, allowing to simulate the space-variant channel impulse response for a moving receiver. Furthermore, the appearance and disappearance of multipath components are geometrically taken into account by an angular pattern. We verify the proposed methodology by simulations. [ABSTRACT FROM AUTHOR]

The next generation of intelligent vehicle systems will use wireless communication to connect a car and its passengers. It is therefore important to understand the in-cabin propagation characteristics of an automobile. This paper investigates the wireless channel native to these cabin enclosures. We present detailed, polarization dependent field measurements over a plane of interest in the cabin, and show that a simple analytical model gives reasonable agreement with our measurements. [ABSTRACT FROM PUBLISHER]

This paper describes an extensive propagation channel measurement campaign in a warehouse environment for line-of-sight (LOS) and nonline-of-sight (NLOS) scenarios. The measurement setup employs a vector network analyzer operating in the 2–8-GHz frequency band combined with an $8 \times 8$ virtual multiple-input multiple-output (MIMO) antenna array. We develop a comprehensive statistical propagation channel model based on high-resolution extraction of multipath components and subsequent spatiotemporal clustering analysis. The intracluster direction of departure (DoD), direction of arrival (DoA), and the time of arrival (ToA) are independent, both for the LOS and NLOS scenarios. The intracluster DoD and DoA can be approximated by the Laplace distribution, and the intracluster ToA can be approximated by an exponential mixture distribution. The intercluster analysis, however, shows a dependency between the cluster DoD, DoA, and ToA. To capture this dependency, we separately model the clusters caused by single and multiple bounce scattering along the aisles in the warehouse. The intercluster DoD distribution follows a Laplace distribution, while the cluster DoA conditioned on the DoD is approximated by a Gaussian mixture distribution. The model was validated using the capacity and delay-spread values. [ABSTRACT FROM AUTHOR]

Based on a ring, a disk, and an elliptical scattering models, the power spectral densities (PSDs) are derived and investigated for fixed-to-fixed (F2F) propagation scenarios with moving scatterers located at a predefined geometry of the models. The velocity distributions of the moving scatterers are assumed to follow uniform, exponential, and mixed Gaussian, and the scatterers can be moving with either low or high speed. The results show that the one ring, the disk, and the model in [14] are very close in describing the PSDs for the F2F radio channels. Moreover, different shape factors have little effect on the PSDs in the disk model. As the shape factor is large enough, the disk model tends to be the same as the one-ring model. The PSDs derived from the elliptical model are different from the one ring and disk models because the scatterers are not only distributed nearby the transceiver, but also distributed along the path between the two ends of the transceiver. [ABSTRACT FROM AUTHOR]

With the aim of providing an overview of the propagation channels in a vehicle engine compartment, narrow-band (1–2 MHz) and broadband (500 MHz) channels in the frequency range from 2 GHz to 7.75 GHz were analyzed. To secure as much generality of analysis as possible, more than 500 propagation channels of seven types of automobiles were measured. The path loss and delay spread were analyzed in terms of distance and frequency. Models that take into account the interdependence of distance and frequency were used, considering that the object sizes in an engine compartment are comparable to the measurement wavelengths. The path-loss exponent for distance was about one below a break point of 450 mm and about three above the break point. The exponent for frequency was around one. The root-mean-square (RMS) delay spread increased as distance increased. Based on the obtained delay spread model, the propagation channel model was finally provided, which is a function of frequency and distance. Then, the channel model was validated by comparing delay spreads calculated from the generated channels and the measured channels. It is also noted that the channel dependence on the types of vehicle was not significant. [ABSTRACT FROM PUBLISHER]

The wireless channel in an industrial environment behaves much differently when compared with wave propagation in home and office environments. This is due to the presence of significant noise and interference caused by large machinery and heavy multipath propagation effects induced by highly reflective structures. In this article, a comprehensive review of radio wave propagation in an industrial environment is presented. The reported channel models and measurement results, at different frequencies and link configurations, of path loss, noise, interference, multipath propagation, and time-varying channel conditions are discussed, and the factors that influence them are highlighted. In addition, open research issues on the propagation of radio waves in an industrial environment are identified. [ABSTRACT FROM AUTHOR]

This article is a review of wireless body-area network (BAN) channel models, with observations about the selection of the best channel model in terms of both first- and second-order statistics. Particular insight into the dominant factors that affect propagation for body-area networks is given. Important second-order statistical measures are discussed, where coherence times and fade durations are of particular interest. The IEEE 802.15.6 standard is used as a basis for the review, with observations and insights given about body-area networks. In this context, narrowband and ultra-wideband (UWB) models are summarized for different measurement environments and carrier frequencies. On-body, in-body, and off-body propagation models are discussed where appropriate. In general, lognormal fading or gamma fading models of the body-area network channel are most applicable. A goodness-of-fit criterion that directly trades off model error and complexity is presented, which gives a new outlook for channel modeling. By this new outlook it is demonstrated that through significant simplification of individual link propagation models for body-area networks, it is possible to combine link models with only a few parameters. Common misconceptions regarding the appropriateness of applying traditional path-loss measures to these short-range networks are then exposed. Finally, the use of relays, which is an option in IEEE 802.15.6, is shown to be important for maintaining reliability in various body-area-network propagation scenarios. [ABSTRACT FROM AUTHOR]

The design of efficient positioning algorithms in navigation satellite systems, like GNSS, operating in land mobile environments demands for detailed models of the radio channel. On the one hand, the models need to accurately describe scattering and shadowing/obstruction caused by vegetation. On the other hand, they have to incorporate the steady change in the propagation constellation due to the receiver displacement. In this paper we propose a model of the non-stationary radio channel in a scenario where a mobile receiver drives past a scattering volume, such as a ball or a cuboid, while the transmitter is elevated, like in satellite positioning applications. Such a volume may represent the canopy of a single tree, the canopies of trees in a grove, or a small forest. Scattering by the volume is characterized by means of multiple point-source scatterers that are assumed to form a marked spatial point process. The system functions of the radio channel are given. An integral form of the time-frequency correlation function of the component in the system functions contributed by the scattering volume is obtained as a direct consequence of Campbell's Theorem. Furthermore, a closed-form approximation of this integral form is derived for time lags corresponding to displacements along the receiver trajectory for which the plane wave assumption holds. The approximation takes into account the steady change in the propagation constellation. The proposed model is validated by means of Monte Carlo simulations and by comparing its prediction capabilities with experimental data in a scenario where a mobile receiver drives past a roadside tree. A good agreement is observed, despite the simplicity of the model. [ABSTRACT FROM PUBLISHER]

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]

Two-dimensional percolation lattices are used to describe urban wireless propagation environment, and random walks are employed to model radio wave propagation. The probability that a generic ray undergoes certain number of collisions at specific spatial location is derived from the Bernoulli equiprobable experiments and the maximum entropy principle. After a probabilistic model of electromagnetic wave propagation is constructed,the analytic closed form of mean received power of electromagnetic rays undergoing random walks at each location is obtained in 2-dimensional channels,which obeys an exponential function of distance. Numerical analysis is used to discuss the precision of the analytic form, which is very satisfied in very wide ranges of parameters. The dependence of received power on geometrical parameters of lattices is also investigated. The results are validated by comparison with experimental data, and the theoretic results correspond well with the experimental data. [ABSTRACT FROM AUTHOR]