Percorrer por autor "Leonor, Nuno"
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- 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.
- Benchmark of radio propagation path loss models applied to line-of-trees at 10, 36 and 60 GHzPublication . Leonor, Nuno; Ramos, Glaucio; Orihuela, Carlos; Mello, Luiz da Silva; Caldeirinha, RafaelIn this paper, measurements conducted in outdoor line-of-trees scenarios at 10, 36 and 60 GHz are used to provide a benchmark between various modeling approaches for radiowave propagation in the presence of vegetation. The list of selected models include the ITU-R P.833-9 recommendation for attenuation in vegetation, and an hybrid approach which uses simple empirical models to characterize the propagation phenomena in the presence of vegetation, and then uses a ray-tracing algorithm to gather all the interactions between the different trees. The performance of the selected empirical model was then assessed against the outdoor measurements and a comparative analysis is provided at the end of this paper.
- Comparative Study of Computational Electromagnetics Applied to Radiowave Propagation in WildfiresPublication . Faria, Stefânia; Vala, Mário; Coimbra, Pedro; Felício, João; Leonor, Nuno; Fernandes, Carlos; Salema, Carlos; Caldeirinha, RafaelIn this paper, a comparative study of four computational electromagnetic techniques to model the 2-dimensional radiowave propagation phenomena in wildfires, is proposed. The fire dynamics for a small tree specimen is studied, in which gases released from the combustion process are used to investigate the generation of an ionised plasma and, thus, to evaluate the gradient of the medium refractive index using the cold plasma model. Consequently, the presence of fire has been demonstrated to introduce additional losses in the radio path that may be critical to radio communication systems that are widely used in mission critical applications. The gradient of the refractive index across the vegetation volume yielded by the cold plasma model is used as input parameter to different numerical methods and electromagnetic solvers at 385 MHz (i.e. TETRA frequency band in Portugal) and, subsequently, their applicability to wildfires is assessed.
- Disruptive Future of Radar Based on All-Digital PN Signal ProcessingPublication . Ribeiro, Carlos; Ferreira Gil, João; Caldeirinha, Rafael; Reis, Joao R.; Sardo, Andre; Duarte, Luis; Leonor, NunoThis paper presents the first results on the design and implementation of a real-time and high resolution monostatic radar at 24 GHz, based on the sliding correlation of pseudonoise (PN) sequences. The real-time radar, with a high time resolution better than 4ns, is used for moving target identification (MTI) in the presence of highly dense clutter, under harsh environments and severe weather conditions (fog, snow and fire smoke or plume). A radar signal processing based on alldigital PN sequences is proposed, which represents a quantum leap in radar future front-end architecture. Results obtained in a controlled environment, inside an anechoic chamber, are presented and a benchmark with a commercially-of-the-shelf solution is presented. © 2019 IEEE.
- 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.
- Experimental Setup for Radio Characterization of Fire at Microwave FrequenciesPublication . Coimbra, Pedro; Faria, Stefânia; Vala, Mário; Felício, João; Fernandes, Carlos; Leonor, Nuno; Caldeirinha, Rafael; Salema, CarlosWildfires are a recurring phenomenon in many countries around the world, either due to natural causes or negligent human behavior. Emergency communication services used by firefighters at the theater of operations must be highly reliable, in order to ensure the safety and coordination of the teams that are fighting the wildfire, contributing to extinguishing it as quickly as possible with minimum use of resources. Emergency communication networks strongly rely on wireless links that may be impaired by the flames. In this work, we present an experimental setup for characterization of fire at microwave frequencies. Preliminary results show that we are able to extract very low dielectric constant (<1.1) using ultrawideband signals. Moreover, we characterize the attenuation introduced by fire in small-scale scenario. Future work will include the characterization of fire in larger-scale scenarios.
- 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.
- A feasibility study on the extension of the point scatterer formulation to raised canopy forestsPublication . Leonor, Nuno; Caldeirinha, Rafael; Sanchez, Manuel; Fernandes, TelmoThis paper presents a feasibility study on the extension of the point scatterer formulation to characterise the electromagnetic behaviour of tree trunk formations. The original propagation model, successfully used in the canopy layer, uses various point scatterers with specific radiation characteristics, distributed within a computational volume, to describe the effect of the trees present in the radiowave propagation path. Subsequently, a ray-tracing based algorithm is used to gather all the interactions between the different point scatterers present in the simulation channel. This propagation model is now extended and applied to the trunk layer. To this extent, re-radiation measurements of both metallic and dielectric cylinders were performed in a controlled environment, inside an anechoic chamber, at 9.4, 18.8 and 37.6 GHz, were used to assess the model performance when dealing with single and isolated tree trunks. The proposed propagation model was then assessed against directional spectra measurements conducted within tree trunk formation scenarios at 9.4, 18.8 and 37.6 GHz. Additionally, a comparison analysis with a discretised radiative energy transfer (dRET) approach is conducted, where a relatively good agreement has been found.
- A feasibility study on the extension of the point scatterer formulation to vegetation mediaPublication . Leonor, Nuno; Caldeirinha, Rafael; Fernandes, Telmo, Telmo Rui Carvalhinho Cunha, Telmo R.; Sanchez, ManuelThis paper aims at the development of a novel ray-tracing based method to characterise and model the electromagnetic behaviour of trees and vegetation volumes. This model uses various point scatterers with specific radiation characteristics, distributed within a computational volume, to describe the effect of the trees present in the radiowave propagation path. Additionally, the method to extract the parameters of the point scatterers from measurements is presented. The performance of this novel formulation was assessed in a tree formation scenario against measurements results obtained in a controlled environment, inside an anechoic chamber, at both 20 and 62.4 GHz.
- 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.