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Radio environment maps (REMs) are beginning to be an integral part of modern mobile radiocommunication systems and networks, especially for ad-hoc, cognitive, and dynamic spectrum access networks. The REMs will use emerging military systems of tactical communications. The REM is a kind of database used at the stage of planning and management of the radio resources and networks, which considers the geographical features of an area, environmental propagation properties, as well as the parameters of radio network elements and available services. At the REM, for spatial management of network nodes, various methods of propagation modeling for determining the attenuation and capacity of wireless links and radio ranges are used. One method of propagation prediction is based on a numerical solution of the wave equation in a parabolic form, which allows considering, i.a., atmospheric refraction, terrain shape, and soil electrical parameters. However, the determination of a current altitudinal profile of atmospheric refraction may be a problem. If the propagation-prediction model uses a fixed refraction profile, then the calibration of this model based on empirical measurements is required. We propose a methodology for calibrating the analyzed model based on an example empirical research scenario. The paper presents descriptions of the propagation model, test-bed and scenario used in measurements, and obtained signal attenuation results, which are used for the initial calibration of the model. [ABSTRACT FROM AUTHOR]

This paper presents an empirical propagation path loss model for corridors in office buildings. The proposed model estimates changeable character of radio signal attenuation, based on a special approach as a combination of the simple free-space model with the author's model. The measurement stand and measurement scenario are described. The propagation path loss research have been made in corridor for different frequencies in range 30 MHz to 290 MHz. A significant number of measurement results were allowed an analysis of the radio wave propagation conditions in the environment. In general, the propagation path loss increases for each measurement frequencies with length of propagation route. Based on measurement data, the new empirical propagation path loss model was developed. For this purpose, the regression analysis was made. The novelty of this model is that it could be used for estimate propagation path loss in measured environment for different radio wave frequencies. At the end, in order to justification the practical usefulness of described method for estimate a radio wave attenuation, the statistical evaluation was made. Thus, the results of the statistical analysis ( ME, SEE and R2 values) are satisfactory for each measured radio wave frequency. [ABSTRACT FROM AUTHOR]

In this work, a 60 GHz empirical investigation on a scale model is performed to give insight into building scattering at 2 GHz. From the presented building scattering measurements, the relative effects of the furniture and building surface on the building scattered signal are determined. The fading statistics of the scattered signal are also determined and are found to be Rayleigh distributed. Lastly, a simple method to compute the scattered power from a building using the effective roughness approach is presented and validated using the measurements. [ABSTRACT FROM PUBLISHER]

This paper presents an empirical study for fixed wireless links based on IEEE802.16 standard in a vegetated residential environment. Field measurements were conducted for suburban microcell channel by utilizing 5.8 GHz of Unlicensed National Information Infrastructure. A set of comprehensive measurements that covered 10 point-to-multipoint links surrounding Universiti Teknologi Malaysia were selected to investigate the impact of vegetation on propagating radio waves. This suburban location was characterized by trees and terrain blockage. The aim of this study is to develop a path loss model that incorporates vegetation effect. Received signal strength and factors influencing the performance of the signal strength are highlighted here. The accuracy of the proposed prediction model is analyzed, which quantifies that path loss is proportional to the distance of the tree to the receiver, size, density, and number of trees within the vicinity of transmitting and receiving antennas. Observation found that external effect, such as wind significantly affect the signal performance too. The terrain was another factor, which needs to consider into account before deployment of wireless links. Depending on the dynamic characteristics of the presence of trees between the communication links, the measurement results show that the path loss is increased from 5.69 to 33.67 dB. The results obtained are compared to Free Space Loss model, Weissberger model, and ITU-R model. Those established models are used to validate the applicability results obtained by means of root mean square (RMS) error. In view of this research work, a good agreement of the proposed excess loss model achieves the smallest RMS error for links obstructed by single tree and the row of trees. [ABSTRACT FROM AUTHOR]

Abstract: Solitary wave evolution over a shelf including porous damping is investigated using Volume-Averaged Reynolds Averaged Navier–Stokes equations. Porous media induced damping is determined based on empirical formulations for relevant parameters, and numerical results are compared with experimental information available in the literature. The aim of this work is to investigate the effect of wave damping on soliton disintegration and evolution along the step for both breaking and non-breaking solitary waves. The influence of several parameters such as geometrical configuration (step height and still water level), porous media properties (porosity and nominal diameter) or solitary wave characteristics (wave height) is analyzed. Numerical simulations show the porous bed induced wave damping is able to modify wave evolution along the step. Step height is observed as a relevant parameter to influence wave evolution. Depth ratio upstream and downstream of the edge appears to be the more relevant parameter in the transmission and reflection coefficients than porosity or the ratio of wave height–water depth. Porous step also modifies the fission and the solitary wave disintegration process although the number of solitons is observed to be the same in both porous and impermeable steps. In the absence of breaking, porous bed triggers a faster fission of the incident wave into a second and a third soliton, and the leading and the second soliton reduces their amplitude while propagating. This decrement is observed to increase with porosity. Moreover, the second soliton is released before on an impermeable step. Breaking process is observed to dominate over the wave dissipation at the porous bottom. Fission is first produced on a porous bed revealing a clear influence of the bottom characteristics on the soliton generation. The amplitude of the second and third solitons is very similar in both impermeable and porous steps but they evolved differently due to the effect of bed damping. [Copyright &y& Elsevier]

Abstract: In this work, the large-wave simulation (LWS) method is adapted for application in spilling wave breaking over a constant slope beach. According to LWS, large scales of velocities, pressure and free-surface elevation are numerically resolved, while the corresponding unresolved scale effects are taken into consideration by a subgrid scale (SGS) model for wave and eddy stresses. The model may be not fully applicable in very shallow water, close to the shoreline, where the unresolved, turbulent, free-surface oscillation is of the same order with the water depth. Time integration of the Euler equations is achieved by a two-stage fractional scheme, combined with a hybrid scheme for spatial discretization, consisting of finite difference and pseudospectral approximation methods. Model parameters are calibrated by comparison to available experimental data of free-surface elevation and velocities in the surf zone for cross-shore incoming waves. The action of the wave SGS stresses in the outer coastal and surf zones initiates breaking and generates appropriate vorticity, in the form of an eddy structure (surface roller), at the breaking wavefront. At incipient breaking, both advection and gravity contribute to the vorticity flux at the free surface, while only after the full development of the surface roller, the effect of advection becomes stronger. The SGS model is also utilized to simulate propagation, refraction and breaking of oblique incoming waves. The gradual breaking and dissipation of wave crestlines and the surface roller structure along the breaking wavefront are automatically captured without any empirical input, such as data for the roller shape or the wave propagation angle at breaking. [Copyright &y& Elsevier]

The evaluation of communication systems with low-height terminals requires path loss models that are applicable to low-height links. For the terminology low-height, the range 0.5 (mobile-) to 3 m (fixed-node) above ground is considered. Herein, empirical non-time-dispersive propagation models for relaying systems with low-height terminals are proposed. The models consist of line-of-sight and non-line-of-sight branches. Single- and two-slope modelling approaches were examined. The models take into account the effect of frequency, transmitter and receiver height and environment. They are complemented by shadowing and fast-fading distribution and correlation statistics. The performance of the models in producing accurate estimations is evaluated by comparison with sets of independent data. [ABSTRACT FROM AUTHOR]

The frequency correlation characteristics of shadowing over television bands in a suburban area are evaluated. Some papers report that shadowing losses are high frequency correlated. However, although the frequency correlations can be modelled as a function of the frequency differences are expected, conventional works only present correlation analyses between two or three channels. The correlations have shown an exponential decrease in proportion to the frequency differences based on several massive datasets measured over the television bands. In addition, the empirical model for the characteristics of the frequency correlations is discussed. An empirical model that consists of two exponential decay models is proposed, and show the Rsquared value for the experimental value is ~1. [ABSTRACT FROM AUTHOR]