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- Extension of the dRET Model to Include Scattering from Tree Trunks in Microcell Urban Mobile ScenariosPublication . Caldeirinha, R. F. S.; Fernandes, T. R.; Leonor, N.; Ferreira, D.This paper proposes a framework for extending the applicability of the discrete RET (dRET) model to accommodate radiowave scattering from tree trunks, particularly in microcell urban mobile scenarios, at micro- and millimetre wave frequencies. This framework aims to provide accurate modelling of the signal emanated inside and around isolated blocks of tree trunks, for instances, in raised canopy forests or in urban street canyons like scenarios. Model validation against measurement results inside an anechoic chamber for a double line of regularly spaced metallic and dielectric trunks at 18.8 GHz, as well as recommendations for a more encompassing model, are presented.
- On the applicability of the dRET model to the trunk layerPublication . Fernandes, T.; Leonor, N.; Caldeirinha, R.; Richter, J.; Al-Nuaimi, M.This paper presents a method to model the scattered signal from a regular formation of cylinders, both dielectric and metallic, at micro and millimeter wave frequencies. The model, aims to predict the signal emanated inside and around an isolated block of tree trunks, and might be used as part of a larger algorithm intended to model isolated volumes of vegetation. The method presented here, is based on the prior knowledge of the re-radiation function of cylinders and used the dRET (discrete Radiative Energy Transfer) model, to gather the interactions between the trunks present in the formation to predict the directional profile of the received signal power level at various location inside the formation. The re-radiation function from cylinders, is predicted based on a model previously applied to lamp posts, and is assessed by comparison with measurements performed at 18 and 36 GHz. These functions are subsequently used to input the dRET model whose predictions were also assessed with measurements obtained inside an anechoic chamber, using the same spot frequencies.
- Analysis of Radiowave Propagation in Forest Media Using the Parabolic EquationPublication . Ramos, Glaucio L.; Pereira, Paulo T.; Leonor, Nuno; Caldeirinha, Rafael F. S.This paper presents preliminary results about path loss prediction in vegetation using the parabolic equation technique. The trees were modelled in a flat and a triangular format and their effect in the path loss was analysed. A real measurement scenario with trees was also modelled and compared with the PE simulation. The use of the parabolic equation method to study the path loss attenuation in forest environments seems to be very promise.
- A Practical Deconvolution Antenna Method to Retrieve Scattering Profile in Complex Random Media - A Vegetation Case Study at 28 GHzPublication . Leonor, Nuno; Fernandes, Telmo; Caldeirinha, RafaelThis paper presents a method to improve the extraction the Radiative Energy Transfer (RET) theory input parameters for application in vegetation attenuation modeling. The input parameters for this model, which are extracted from specific measurement data, are normally influenced by the radiation pattern of the receiver antenna. A new method to improve the accuracy of the scattering function parameters obtained from measurements is presented. This method is based on the prior analysis of the antenna's radiation pattern distortion while measuring the scattering function, allowing the development of calibration curves, to correct the distorted propagation parameters. The proposed method was tested with measurements conducted inside an anechoic chamber, using real small indoor trees, mimicking a forest scenario using various different receiver antennas at 28 GHz, and the model accuracy improvement was assessed at various vegetation depths.
- Shielding Effectiveness of Log Barriers for Radio Exclusion ZonesPublication . Conniott, W.; VITORINO REIS, JOÃO RICARDO; Leonor, Nuno; Caldeirinha, RafaelThis paper presents the development of new electromagnetic barriers based on wooden poles for application in electromagnetic site shielding. Exposure to electromagnetic radiation becomes a raising concern among the population worldwide, mostly due to the explosion of mobile technologies and services. A number of innovative and highly sustainable barriers made of circular section timber of low industrial processing, based on periodic structure of wooden poles that are stacked in a multi-layer configuration, while allowing visual transparency, is proposed. Immediate applications may be found in electromagnetic barriers that may be placed at intended radio exclusion zones in the [0.7, 2.5] GHz frequency range. © 2018 Institution of Engineering and Technology. All rights reserved.
- Estimation of dielectric concrete properties from power measurements at 18.7 and 60 GHzPublication . Feitor, Bruno; Caldeirinha, Rafael; Fernandes, Telmo, Telmo Rui Carvalhinho Cunha, Telmo R.; Ferreira, David; Leonor, NunoIn this paper, microwave and millimetre wave reflection coefficient measurements at 18.7 and 60 GHz are presented for a group of concrete slabs, in which only the thickness of the gravel present inside is varied. An empirical reflection coefficient value is determined using both reflected and LOS power measurements. A concrete slab with no gravel is used as a reference. The measurement results show the dependence of the reflection coefficient with the thickness of the gravel inside the slab. The measurement results allow for the appropriate extraction of dielectric properties of the materials under study.
- A simple scattering model for tree trunksPublication . Leonor, Nuno; Ferreira, David; Caldeirinha, Rafael; Fernandes, Telmo, Telmo Rui Carvalhinho Cunha, Telmo R.; Ferreira, DavidThis paper presents the work carried out in an effort of modelling the scattering and absorption effects of single tree trunks with application to the discrete Radiative Energy Transfer (dRET) based model applications. The assessment of the proposed empirical model was performed against measurements of both metallic and dielectric cylinders, mimicking tree trunks, at several micro- and millimetre wave frequencies, i.e. 9.4, 18.8 and 37.6 GHz. These were carried out in a controlled environment, i.e. an anechoic chamber, so that frequency dependent effects could be evaluated.
- Real‐time high‐resolution radio frequency channel sounder based on the sliding correlation principlePublication . Ferreira, David; Caldeirinha, Rafael F. S.; Leonor, NunoA channel sounder based on the cross‐correlation properties of pseudo‐noise random sequences, known as swept time delayed cross‐correlation channel sounder, is presented. This sounder enables the characterisation of doubly selective channels, providing both amplitude and Doppler spectra information. It performs real‐time measurements of specific radio channels with a high resolution of 2 ns for adjacent multipath component, and a current maximum Doppler spread of ±100 Hz, but that can go beyond ±1 kHz, if some components are upgraded. The amplitude measurements given by the sounder, presented as power delay profiles, have a dynamic range of about 35–40 dB. This study provides detailed information on the most relevant components used to develop the sounder, and presents some of the calibration measurements performed on the bench, as well as specific radio frequency measurements at 18.7 and 60 GHz in a controlled environment. Finally, improvements that are feasible to be implemented in the near future are proposed.
- A Framework for the Analysis of Wildfire Effects in Emergency Communication SystemsPublication . Leonor, Nuno; Fernandes, Carlos A.; Salema, Carlos; Caldeirinha, RafaelThis paper aims at the development of a simulation framework to enhance the quality, performance and the resilience of the emergency radio communication systems during a wildfire event. To this extent, this research work includes several studies that will contribute for the better understanding of the propagation effects on radio signals under fire environments, the development of a fire-front building up model, the development of a radio propagation tool to obtain coverage maps based on relevant models for propagation in rural areas, particularly in highly dense forest areas, taking into account the topography and clutter in the radio path and the integration of wildfire build up models into the radio propagation tool for an all encompassing radio coverage tool to aid ground forces in realtime with identification of radio exclusion zones in real-time as fire-front develops.
- Extension of the dRET Model to Forests of Thin CylindersPublication . Leonor, Nuno; Ferreira, David; Caldeirinha, Rafael; Fernandes, Telmo, Telmo Rui Carvalhinho Cunha, Telmo R.; Manuel Garcia SanchezThis paper presents a feasibility study on extending the applicability of the discrete radiative energy transfer (dRET) model to the trunk layer of raised canopy forests. The framework herein presented, proposes a method to predict the scattered signal inside and around a formation of cylinders (mimicking thin tree trunks), which is based on the prior knowledge of the cylinder 2-D reradiation pattern as input parameters to the dRET model. The characterization and modeling of the cylinder 2-D reradiation patterns were performed in an anechoic chamber, so that frequency-dependent effects could be evaluated. The assessment of the proposed method was performed against measurements within a formation of both metallic and dielectric cylinders mimicking thin tree trunks, at micro- and millimeter-wave frequencies, i.e., 9.4, 18.8, and 37.6 GHz.