Pavel Pechac

Elevation Dependent Shadowing Model for Mobile Communications via High Altitude Platforms in Built-Up Areas

An empirical propagation prediction model is described for mobile communications from high altitude platforms (HAPs) in different types of built-up areas. The model introduced here is defined as a function of the angle of elevation. The target frequencies are selected from the 2 to 6 GHz frequency band prospective for 3G and 4G mobile systems, namely at 2.0,3.5, and 5.5 GHz. This new HAP model recognizes two cases - line of sight (LOS) and non-line of sight (NLOS) between a HAP and a user at street level. The simulation of the urban environment is based on a statistical approach. Additional shadowing path loss is calculated using the uniform theory of diffraction for NLOS conditions. Normal distribution of the additional shadowing path loss was distinguishable from the simulation results. The shadowing path loss is defined as a function of the elevation angle. The results of the empirical model developed for idealized conditions are verified by measurements taken from a remote-controlled airship in different types of urban environment. Close correlation was achieved between the theoretical model and the experimental data. The HAP elevation dependent shadowing model is easy to implement and can be used for realistic planning and simulations of mobile networks provided via HAPs in built-up areas.

Estimation of the Refractivity Structure of the Lower Troposphere From Measurements on a Terrestrial Multiple-Receiver Radio Link

A matched field technique is used for remote sensing of refractivity profile. The method relies on electromagnetic propagation simulation to estimate the height profile of radio refractivity in the lower atmosphere by comparing theoretical predictions with measurements on a terrestrial radio link. The objective is to discover whether small variations of the airs refractive index can be detected in the lowest part of atmosphere, up to 150 m above the ground. The resultant estimations of the height profile of refractivity are compared with the measured refractivity profile obtained from meteorological sensors at different heights. The results show a close agreement between the estimated and measured refractivity profiles during periods of deep fading events.

The UAV Low Elevation Propagation Channel in Urban Areas: Statistical Analysis and Time-Series Generator

In this paper we analyze the fading statistics of the link between a remotely controlled flying platform or an Unmanned Aerial Vehicle (UAV) and a ground receive station in an urban area. This link has a very specific geometry which is somewhere in between that of the purely terrestrial case (e.g., a macro-cell) and that of the land mobile satellite (LMS) systems. We have performed a model-based statistical analysis using unique experimental data, and following well-known models for LMS and terrestrial links with the conclusion that the Loo [1] (Rice+log-normal) model is the most suitable starting point for developing the wanted model; then several modifications have been introduced achieve a better match. Finally, we developed a narrowband time-series generator capable of reproducing the observed signal dynamics.

Intelligent walls as autonomous parts of smart indoor environments

This study introduces the concept of an intelligent wall as an autonomous part of a smart indoor environment for cognitive wireless networks. Here, an intelligent wall is a wall inside a building equipped with an active frequency-selective surface, simple low-cost sensors and a cognitive engine with machine-learning ability. Using simulations, it has been shown that the smart environment based on intelligent walls can react to the immediate demands of an indoor wireless system, control radio coverage and, consequently, influence the overall system performance. The concept of the intelligent walls is described and evaluated based on a simple implementation of an arrangement of two intelligent walls in a conference centre scenario. Artificial neural networks were employed in the cognitive engine. Elementary orthogonal frequency division multiple access static system simulations are used to analyse the influence of the smart environment on the system performance. Results are discussed in detail and typical characteristics of the aforementioned system are derived and summarised.

UHF Propagation in Caves and Subterranean Galleries

An experimental study is described on the natural propagation of UHF band radio waves in straight subterranean galleries. An extensive measurement project took place in five underground localities and, based on the experimental data, an empirical model of radio wave transmission was derived. The model was calibrated according to the measurement data and compared with the theoretical waveguide approach to propagation prediction. The presented results can be used for the practical planning of wireless communications in speleology applications and as an experimental basis for further theoretical works

Domain Decomposition Algorithm for Complex Boundary Modeling using the Fourier Split-Step Parabolic Equation

This paper addresses the use of parabolic equation in radiowave propagation problems involving impedance-boundary modeling. The Fourier split-step technique for solving the parabolic equation provides numerical efficiency but lacks the ability to represent complex boundary conditions. A method that makes use of the domain decomposition technique to solve two-dimensional problems of impedance-boundary modeling using the Fourier split-step technique is introduced. A test case, using an urban scenario represented by buildings with various electrical parameters, was used to validate the results given by the method with results obtained by geometrical optics

Building Penetration Loss for Satellite Services at L-, S- and C-band: Measurement and Modeling

An extensive measurement campaign, covering a representative set of typical buildings in an urban area and aimed at building penetration loss for satellite services at L-, S- and C-band, was performed in Prague in the summer of 2009. Throughout the measurements, a remote-controlled airship was used as a pseudo-satellite carrying a transmitter which provided unmodulated continuous wave left-handed circularly polarized signals at 2.0 GHz, 3.5 GHz, 5.0 GHz, and 6.5 GHz. A description of the measurement campaign is provided here, together with a thorough analysis of the resulting experimental data. A significant dependence on elevation angle is reported for line-of-sight and non-line-of-sight propagation conditions separately. Subsequent steps to introduce elevation dependent empirical models at corresponding frequencies follow. Finally, a comparison to other studies dealing with building penetration loss for high elevation angles is presented.

Frequency Dependence of Attenuation Due to Vegetation for Satellite Services

This letter presents the results of vegetation loss measurements at 2.0, 3.5, 5.0, and 6.5 GHz for elevation angles ranging from 20° to 90°. The excess attenuation due to vegetation was measured at four different wooded locations using a remote-controlled airship as a pseudo-satellite. Measurements taken in an open field were used as a reference. The results are given as additional attenuation averaged over the whole range of azimuth and elevation angles for circular polarization. Average results from all four locations vary from 9 dB at 2.0 GHz to 14.5 dB at 6.5 GHz. Linear frequency dependence of vegetation attenuation was observed, and a corresponding empirical model providing the additional vegetation loss as a function of the frequency was derived in closed form. The results are then compared to the literature.

Excess Loss for High Elevation Angle Links Shadowed by a Single Tree: Measurements and Modeling

Results of experiments focusing on high-elevation links with a ground terminal shadowed by a single tree are introduced. The measurement trials were carried out at 2.0, 3.5, 5.0 and 6.5 GHz utilizing a remote-controlled airship as a pseudo-satellite for four different deciduous trees in summer and winter when trees are in full leaf and defoliated. The complete range of elevation angles typical of satellite/HAP services was addressed. Empirical models were proposed to account for excess loss as a function of its geometry. The applicability of terrestrial vegetation attenuation models on the given scenario is discussed.

Advanced 3D indoor propagation model: calibration and implementation

A software tool, implementing a semi-deterministic model which provides swift predictions, accounts for all significant physical phenomena while utilising a clear-cut description of material properties, is presented in this article. The software can predict signal coverage, delay profiles and angle of arrivals for receivers located anywhere in a scenario using three probabilistic parameters to describe each of the materials. Probabilistic parameters can be efficiently optimised based on measured data by a genetic algorithm optimiser contained in the software tool enabling real material properties (constants) to be avoided. The semi-deterministic model is briefly described whereas its implementation into the tool is explained in greater detail. Measured narrowband, as well as wideband, data are presented, and the basic principles of the computer optimisation utilised in the tool are shown. Optimised results are compared with the measured ones and deviation is determined. The principle of a simple multi-threading algorithm which improves the tool performance while decreasing time consumption is presented along with computational times where a different number of threads are compared.