-In almost all literature about propagation models through vegetated environments, path loss has been proposed based on specimens of temperate clime conditions. In this work, a new propagation model is proposed, based on measurements, carried out on vegetated environments with tropical specimens. These environments are common on suburban and rural areas in Brazil. Current models have presented pessimistic approach to propagation loss in these areas. The vegetal morphology and frequency effects, transmission height and distance are taken into consideration. Finally a comparison with existing models is presented.Index Terms-Path Loss over vegetated environments, UHF Propagation Model, Radio communication fading. I. INTRODUCTIONThere is a great interest in fading and attenuation of electromagnetic signals associated with vegetated environments at low UHF frequencies. However it remains under exploited in the literatureThe 700 -800 MHz band has been proposed in several countries to use on new communications technology, due to its very good propagation condition [2], leading to better signal coverage with less energy cost. In Brazil this is a very important issue and new 5G communication systems are being proposed to cope with the growing demand. The goal of this paper is to develop a prediction model for the signal attenuation due to the presence of typical tropical vegetal morphologies in the environments, using an empirical mathematic model.The problem of vegetated environment propagation has a great practical interest and it is considered a very complex propagation problem. The propagating wave experience absorption, scattering attenuation and depolarization and these aspects are related with frequency, atmospheric conditions, antenna height, electric properties of the medium, density and morphology of the vegetation specimens. The large amount of aspects makes the problem a very intricate to solve, since they introduce randomness and non-linearity. Vogel e Goldhirsh [3] demonstrated that an isolated tree can attenuate 10 dB the electromagnetic field. This motivates an empirical approach, based on measured data. In order to accomplish that, an extensive measurement campaign was carried out on the band of In built up areas, the edifications produce signal variations due to wave scattering. On vegetated environments, the trees can be characterized as such causing scattering and attenuation of the signal.According with Jao [5], it is possible to consider the vegetation as a randomly distributed medium with different kinds of trees. There is a great vegetal diversity, making its characterization difficult.However, due to the low attenuation produced by grassy and bushes, the characterization effort on this work will be concentrated over arborized environment, which play the major role in path loss.The characterization of the vegetation was a simplified form of the methodology presented by Kafaru [6], where the area is divided into squares, with specific morphology that includes density size and type of trees...

This paper presents the preliminary results of channel characterization in the 700 MHz band, based on measurements of an OFDM modulated signal in urban and rural environments. This band will be used for mobile wideband communications in Brazil. An investigation of the dispersion parameters of the channel was carried out in the two different environments aiming a comparison between results of mean excess delay and RMS delay spread, useful for systems design.

This paper presents preliminary results of field measurements carried out for evaluating the operation of the ISDB-TB standard digital TV in the VHF-high band. Measurements were performed in urban, suburban and rural areas in a medium-sized Brazilian city. The analysis includes results of static reception measurements for evaluating the received field strength and the signal to noise ratio thresholds for correct signal decoding. A comparison with theoretical values of field strength is also presented.

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Resumo-Este trabalho apresenta o desenvolvimento de um transmissor para um leitor RFID apropriado para uma etiqueta sem chip específica, contornando a limitação de frequências de trabalho de leitores comerciais. O objetivo é apresentar os testes de transmissão feitos em laboratório para a fabricação de um transmissor para um leitor com custo mais baixo e apropriado para operar na faixa de frequências de uma etiqueta sem chip, também fabricada em laboratório, utilizando um Arduino DUE.

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Starting from outdoor transmission, crossing vegetation, the wideband and narrowband characterization of the indoor mobile radio channel in the 700 MHz band is obtained from experiments carried out in the indoor environment of the Engineering building at Fluminense Federal University, and from the processed data, respectively, the power-delay profiles obtained permitted to calculate the time dispersion parameters and the envelope of the signal permitted to adjust probability density functions to the signal variability, concluding about the influence of vegetation on those characteristics.

Abstract-This paper deals with the effect of the Single-Input Multiple-Output spatial diversity on the OFDM mobile radio signal propagating in an urban channel. From measurements performed in Rio de Janeiro city, Brazil, by using two receiving antennas at diversity, the calculated capacity presented an improvement when compared to the individual one.Index Terms-delay spread, OFDM , SIMO, spatial diversity, urban channel. I. INTRODUCTIONOver the last years, the OFDM (Orthogonal Frequency Division Multiplexing) technique has received special attention to the mobile radio communication in the cellular systems [1][2][3]. Since the available bandwidth is divided into narrower bands, each one experimenting flat fading, this technique presents robustness against time-varying frequency-selective fading. Therefore, such technique offers advantages considering its ability in dealing with high-data-rate transmissions over dispersive channels with low equalization complexity [3]. It is also an efficient solution to operate in Non-LineOf-Sight (NLOS) conditions, normally subject to multipath fading, because it uses cyclic prefix (CP) in order to avoid intersymbol interference. However, the mobility demanded by the users degrades the received signal, worsening it due to the increasing speed which leads a Doppler shift that desynchronizes the OFDM subcarriers, consequently, causing intercarrier interference [4].There have been some solutions to improve final user's delivered signal. Among them is the spatial diversity which is most referred in several studies and it has been used in the reception of the OFDM signal. Ali et al. deals with simulations of blind estimation techniques that exploit the receive antenna diversity [5]; Yagishita et al. [6] studies the effects of diversity in the receiving antenna using Fasterthan-Nyquist (FTN) signaling in a multipath fading channel; Kim et al. [7] analyzes the macrodiversity in LTE-Advanced. However, most of results presented in those studies were obtained from simulations. In this context, this paper provides experimental results for the capacity obtained in a 2.48 GHz band using the spatial diversity in a SIMO (Single-Input Multiple-Output) system. Two branches were used in the reception of a 40 MHz-OFDM signal in the 2.48 MHz band. In order to accomplish it, an urban channel was sounded and the signals from both branches of diversity were