Ana Vazquez Alejos

Measurement and Analysis of Propagation Mechanisms at 40 GHz: Viability of Site Shielding Forced by Obstacles

Mitigation of interference among adjacent radio systems is a topic of growing interest as the spectrum occupation increases. Site-shielding techniques appear as a method of improving millimeter-wave wireless communication system design, allowing frequency reuse and reducing cochannel interference. The viability of applying such techniques to systems operating in frequency bands around 40 GHz is the aim of this paper. Several propagation mechanisms are experimentally studied, including transmission across building obstacles, depolarization, reflection, and diffraction. The performance of some theoretical models of the different scattering mechanisms has been compared with measurement results. The measuring and processing procedures have also been improved. Values of the dielectric parameters of the materials in this frequency band have been obtained and are given in this paper. The attenuation results indicate that various materials, such as mortar, brick, and concrete walls, that present large values of attenuation in decibels per centimeter, can be used to shield base stations, reducing the frequency reuse distance in radio cellular networks. It can also be concluded that there is a significant diffracted field in the shadow region of brick corners.

PROPAGATION ANALYSIS AND DEPLOYMENT OF A WIRELESS SENSOR NETWORK IN A FOREST

A complete study for the deployment of a wireless sensor network in a forest based on ZigBee is presented in this paper. First, due to the lack of propagation models for peer to peer networks in forests, propagation experiments were carried out to determine the propagation model. This model was then used for planning and deploying an actual wireless sensor network. The performance of the network was compared with the expected theoretical behavior to extract some conclusions that are presented in the paper. Finally, some general conclusions, as an estimation of the minimum number of routers necessary to cover a given area, are extracted from the experiments and presented in the paper.

Analysis of Brillouin Precursor Propagation Through Foliage for Digital Sequences of Pulses

In this letter, we investigate the propagation of Brillouin precursors through dispersive foliage media, using leafy vegetation dielectric models proposed by Fung-Ulaby, El Rayes-Ulaby, Brown-Curry-Ding, Maetzler, and Pearce. A fast-Fourier-transform-based formulation is used to analyze the peak amplitude decay and pulse broadening effect (or effective oscillation frequency) related to the precursor formation for both single pulse and sequence of pulses traveling through the leafy vegetation. The influence of the Brillouin precursor on the receiver structure is also investigated. Simulations have been carried out in frequency bands between 100 MHz and 6 GHz allocated for remote sensing applications and digital satellite communications.

Experimental Dynamical Evolution of the Brillouin Precursor for Broadband Wireless Communication through Vegetation

In this paper, we report experimental results on detecting and analyzing the Brillouin precursor through vegetation at frequencies from 500MHz to 3GHz. An experimental method to collect data is reported. The outcomes in terms of energy and time-spreading are presented using modulated rectangular and Gaussian pulses, as well as a sequence of rectangular pulses. Using fleld-collected data, this study shows the estimated dynamical evolution of the Brillouin precursor flelds for wideband wireless systems, such as those represented by IEEE 802.16. The advantages of Brillouin precursors in terms of power spectrum density and bit energy are discussed. Complex relative permittivity is extracted from the experimental data and is used in theoretical formulation to analyze dispersive propagation for any kind of input waveform. Finally, a near-optimal pulse is proposed to achieve maximum propagation distance and/or signal-to-noise ratio for the transmission of bit stream sequences through vegetation.

Urban wide-band measurement of the UMTS electromagnetic environment

Measurements of impulsive noise in the universal mobile telecommunications system (UMTS) electromagnetic environment in urban areas have been conducted and its effect on the UMTS system is analyzed. An impulsive noise-measurement system for the UMTS frequency band has been designed and built, which meets and improves the main features of classical equipments used to measure noise, offering inphase and quadrature outputs simultaneously. This measurement system was carefully calibrated before a measurement campaign was conducted in an urban environment to get impulsive noise statistics. Results show that noise pulses may have high power, long duration, and high repetition rate, so the performance of UMTS could be significantly reduced.

Estimation of Power Extinction Factor in Presence of Brillouin Precursor Formation Through Dispersive Media

In this paper, we analyze the advantages of the Brillouin precursor formation through dispersive media for a given modulated monopulse signal. The algebraic power extinction factor associated with the formation of Brillouin precursor appears to be in charge of the optimized propagation distance within the dispersive media. The analysis has been done in UHF band for rectangular and Gaussian pulses for three different dispersive media, namely, triple distilled water, vegetation and soil. It appears that Brillouin precursors will form given a suitable pulse configuration within a proper frequency window that is related to the dielectric model of the underlying media.

Modelling and Measuring Reflection Due to Flat Dielectric Surfaces at 5.8 GHz

Indoor radio channel planning tools implement different models to simulate propagation mechanisms such as transmission or reflection. The specular reflection formulation is commonly used instead of more complete scattering models. This happens because its coding is less complicated and the software runs faster than when considering reflection in all directions, not yet specular. In this paper, results from measurements are presented, consisting of the effect of constructive walls on an oblique incident wave. These experimental outcomes are modelled by means reflection pattern computations. Physical optics scattering model is used in its classical formulation, and it is then modified to take into account antenna pattern effects in the measurements. The comparison between measurements and simulations is also presented, showing good agreement. Measurements show that low reflective walls produce reflections in several directions across the incidence region. In these situations, the use of algorithms that compute reflection pattern, instead of just specular reflection coefficients, will lead to better agreement with actual results

Interference and impairments in radio communication systems due to industrial shot noise

Measurements of radio impulsive noise in industrial and urban electromagnetic environments have been conducted and its effect on radio communication systems is studied. An impulsive noise measurement system has been designed and built. It meets and improves the main features of classical equipments used to measure noise, offering both in-phase and quadrature outputs simultaneously. The system was carefully calibrated before a measurement campaign was conducted in industrial and urban environments to get impulsive noise statistics. Results show that shot noise events are less frequent in the industrial than at the urban environment, but when a noise event occurs, noise pulses appear more grouped in bursts, exhibit larger amplitude and wider bandwidth. In both cases, shot noise pulses have very high amplitude, long duration and high repetition rate, so the performance of radio communication systems could be significantly reduced in the industrial environment. The effect of the noise burst on digital radio communication systems using different types of modulation is analyzed.

Empirical Pseudo-Optimal Waveform Design for Dispersive Propagation Through Loamy Soil

Using a fast Fourier transform-based theoretical formulation as a starting point for a near-optimal waveform design, three near-optimal or pseudo-optimal pulses are empirically derived in this letter to achieve near-optimal penetration depth through the sample of loamy soil considered in this study. We describe three methods to derive these waveforms with improved features valid for any dispersive media: the first of them establishes a close approach of the Brillouin pulses; and the other two analyze structures that reinforce the Brillouin precursor formation to simultaneously achieve improved peak decay and reduced pulse broadening. The pulses are tested for experimental data achieved within a reduced range of frequency, 0.5-3 GHz, even that any theoretical dielectric model can be also used.

Experimental Detection and Characterization of Brillouin Precursor Through Loamy Soil at Microwave Frequencies

This study reports experimental results on detecting Brillouin precursors through loamy-soil dispersive media in the frequency range of 500 MHz to 3 GHz. An experimental technique to collect and analyze the data is presented. Brillouin precursors are shown to be superimposed on the sine-modulated rectangular and Gaussian pulses. The detected Brillouin precursor is shown to have an algebraic amplitude decay behavior through the wet loamy soil considered in this study. Further, a method is proposed to extract the complex dielectric permittivity of the soil from limited experimental data. The experimental results are validated using a theoretical Fast Fourier Transform-based formulation and the experimentally achieved complex dielectric permittivity. These results are also compared with those of using existing theoretical dielectric models. Three different tests are also applied to validate the hypothesis of Brillouin precursor formation.