Loading...
14 results
Search Results
Now showing 1 - 10 of 14
- 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.
- 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.
- STDCC radar at 24 GHz: first measurement trialsPublication . Ferreira Sardo, Andre; Reis, João R.; Duarte, Luis; Leonor, Nuno; Ribeiro, Carlos; Caldeirinha, Rafael F. S.This paper presents the first measurement trials for performance assessment of a real-time and high resolution monostatic radar operating at 24 GHz. The proposed real-time radar, which operates based on the sliding correlation of pseudo-noise (PN) sequences, provides a high time resolution better than 4 ns, useful 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). The STDCC radar target detection capability is demonstrated in this paper, by measuring and identifying the radar data for 4 distinct scenarios, composed of multiple targets (up to 8), inside an anechoic chamber, demonstrating the potential of the proposed radar architecture.
- 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.
- Satellite‐Terrestrial Channel Characterization in High‐Speed Railway Environment at 22.6 GHzPublication . Ma, Lei; Guan, Ke; Yan, Dong; He, Danping; Leonor, Nuno R.; Ai, Bo; Kim, JunhyeongThe integration of satellite and terrestrial communication systems plays a vital role in the fifth-generation mobile communication system (5G) for the ubiquitous coverage, reliable service, and flexible networking. Moreover, the millimeter wave (mmWave) communication with large bandwidth is a key enabler for 5G intelligent rail transportation. In this paper, the satellite-terrestrial channel at 22.6 GHz is characterized for a typical high-speed railway (HSR) environment. The three-dimensional model of the railway scenario is reconstructed and imported into the Cloud Ray-Tracing (CloudRT) simulation platform. Based on extensive ray-tracing simulations, the channel for the terrestrial HSR system and the satellite-terrestrial system with two weather conditions are characterized, and the interference between them are evaluated. The results of this paper can help for the design and evaluation for the satellite-terrestrial communication system enabling future intelligent rail transportation.
- 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.