Maurício Henrique Costa Dias

On the Use of Wavelet-Based Denoising to Improve Power Delay Profile Estimates from 1.8 GHz Indoor Wideband Measurements

This work presents an alternative processing scheme to improve measurement-based power delay profiles (PDP) estimates, using wavelet-based denoising. The usual PDP processing comprises cutting off all the data below a previously determined flat noise threshold. The proposed method is a more refined approach, since it tries to extract the noise from the measured data, keeping only the estimated signal. Wavelet denoising can be performed in many different ways, for it depends on several parameters, like the noise threshold selection rule, the wavelet function, the choice or not for a wavelet coefficients shrinkage and the number of decomposition levels. Several parameter combinations have been tested, in special for the Visu selection rule, which presented the best performance for the available data in the overall. Denoising was applied to real data from indoor environments, collected from wideband channel sounding surveys, centered at 1.8 GHz. Since frequency domain sounding has been carried out, denoising has been tested both directly over the frequency domain, and over the time–delay domain (PDP). The major result of the proposed processing was a qualitative improvement of the PDP, with smoother noise floors, and also with increases up to 8 dB on signal-to-noise ratios, in special for delay domain denoising.

Mobile indoor wide-band 1.8 GHz sounding: measurement-based time dispersion analysis

The results of a 1.8 GHz indoor wideband channel sounding survey in some typical environments, trying to account for pedestrian subscriber mobility, are presented. The sounding technique has been based on the classical frequency domain, with an optic link instead of coaxial cables providing an extended path range, up to 350 m. Three different scenarios have been analyzed. Complete small and large-scale time dispersion analysis have been derived from the impulse responses measured, like mean delay, rms delay spread, coherence bandwidth and its variations with mobility. From the whole analysis carried out, two main results are worth remarking upon: the power delay profile variation with distance providing a pictorial representation of the main scattering mechanisms of the environment; and the validation of a lower bound relation between the coherence bandwidth and the rms delay spread.

An Empirical Model for Propagation Loss Through Tropical Woodland in Urban Areas at UHF

A vegetation path loss model was derived from measurements performed in a downtown park in Rio de Janeiro city, from 0.9 to 1.8 GHz. The resulting equation followed the general formulation in ITU-R Recommendation P.833. A comparative analysis was carried out with other empirical models, assessing statistical adherence to the available data. Coherent results were observed.

Proficiency testing of electromagnetic compatibility (EMC) labs in Brazil by measurement comparisons

This work reports the analysis and main results of a recently concluded proficiency testing round with the major electromagnetic compatibility (EMC) laboratories in Brazil. Seven labs conducted radiated emission measurements at their test facilities under the coordination of an independent third party supervised by the Brazilian accreditation body, INMETRO. Six of them are currently the only labs accredited on EMC measurements in Brazil. The guidelines of international standards such as ISO/IEC Guide 43 and ISO 13528 were followed, while the scope of the tests focused on EMC compliance of information technology devices, based on CISPR 22. A multi-tone signal generator was specifically designed and assembled for the present proficiency testing conditions. Statistical metrics such as z-score and normalized error have been adopted to assess global and individual performances of the participant laboratories. The normalized error indicated 10 unacceptable results out of 35 results, while only 3 out of 35 z-scores were out of the acceptance range. Considering that the participant labs are actually only for test measurements (not for calibration), the overall performance may be taken as satisfactory, based on the fact that the z-score should be used in this case.

A dual band steerable cell phones jammer

Efficient jamming of cell phones is highly demanded by security authorities in Brazil, especially within prisons. In this context, a dual band steerable jammer structure is proposed in this work. A single spatial filter was designed to operate simultaneously on both cell phone frequency bands, based on the methodology of null steering beamforming. Hardware and software issues of the proposed jammer are addressed. The jammer directional performance is illustrated by simulated beam patterns, which led to acceptable results.

Practical design of a broadband modified monopole by the use of staircase parasitic rings

The present paper discusses the use of parasitic elements to significantly increase the bandwidth of an antenna. In a recent work, the use of staircase metallic rings around a monopole antenna was proposed, leading to bandwidth increments of almost 10 times. However, there were a few shortcomings regarding implementation and experimental validation of that approach. This text reassesses it, with special attention to practical aspects. More specifically, a solid dielectric base is proposed to sustain the rings around the monopole. A prototype has been assembled and tested, with increase in bandwidth comparable to the one achieved in that work.

On the use of Tamir's model for site-specific path loss prediction of HF/VHF systems in forests

One of the most referenced analytical methods to calculate the HF and VHF radio propagation loss in forests is Tamirs model. Though it is very straightforward for point-area radio coverage planning, its extension for site-specific predictions is actually an open problem. In the present work, a heuristic approach is proposed to this matter, when digital terrain and treetops heights models are available. Preliminary outcomes were computed by a Matlab code implementation of the adapted model. Coherent results were observed, with a “height gain” typical of site-specific methods clearly standing out.

VHF/UHF urban sites coverage planning with special care to mixed terrain transitions

This work addresses the main features of a coverage planning algorithm for VHF/UHF low power radio communications systems operating at urban sites, in which special attention was given to mixed terrain clutter transitions. Most of the available commercial prediction tools adopt rough solutions to some problems derived from the use of semi empirical models with geographical databases. The influence of mixed-path terrains and the path loss due to dense vegetation are typical related examples of usually overlooked aspects. The developed code is based on Hatas semi-empirical approach with additional point-to-point adjusts, and includes specific procedures for those two aspects. It has been developed as Matlab™ routines, which were evaluated comparing its outputs to the ones obtained from the use of a commercial planning tool. Results were coherent with the specific features of the site chosen for the analysis.

RF jamming coverage prediction at mixed-path urban scenarios

This work describes an algorithm for VHF and UHF jamming coverage prediction at mixed-path urban scenarios. The proposed algorithm comprised propagation aspects usually overlooked: the influence of mixed paths and dense vegetation. It was developed as Matlab codes to perform coverage prediction for the jammer and the target system, and to compute the respective jamming to signal ratio (J/S) for the analyzed region. Jamming coverage is determined comparing J/S to the target system effective jamming threshold. The proposed tool is useful for jamming operation planning, since it is able to point out unobvious coverage spots that otherwise would be unnoticed.

Improving 900 MHz otdoor measured wideband power delay profiles with wavelet denoising

This work presents new results of wavelet-based denoising as an alternative processing scheme to improve measurement-based power delay profiles (PDP) estimates. The usual PDP processing comprises cutting off all the data below a previously determined flat noise threshold. Denoising is a more refined approach, since it tries to extract the noise from the measured data, keeping only the estimated signal. Recently, it has been successfully applied to real data from indoor environments, collected from wideband channel sounding surveys, centered at 1.8 GHz. Here, the processed data sets were measured outdoors, with 900 MHz carriers. Noise behavior was the worst in the outdoor survey, with variable noise floors during the acquisitions. Yet, signal-to-noise and dynamic range ratios were also lower. Nevertheless, as in the indoor previous experiment, a qualitative improvement of the PDPs has been observed in the outdoor data. Actually, the improvement has been even clearer than the previous one, mainly due to the harsher noise conditions.