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- Jamming detection in GNSS signals using the sample covariance matrix.Publication . Nunes, Fernando; Sousa, FernandoWe propose a blind method to detect interference in GNSS signals whereby the algorithms do not require knowledge of the interference or channel noise features. A sample covariance matrix is constructed from the received signal and its eigenvalues are computed. The generalized likelihood ratio test (GLRT) and the condition number test (CNT) are developed and compared in the detection of sinusoidal and chirp jamming signals. A computationally-efficient decision threshold was proposed for the CNT.
- Exposure assessment to ionizing radiation in the manufacture of phosphate fertilizerPublication . Estevez, J. Gil; Nunes, FernandoPresent study develops and implements a specific methodology for the assessment of health risks derived from occupational exposure of workers to ionizing radiation in the fertilizer manufacturing industry. Negative effects on the health of exposed workers are identified, according to the types and levels of exposure to which they are subject, namely an increase of the risk of cancer even with long term exposure to low level radiation. Ionizing radiation types, methods and measuring equipment are characterized. The methodology developed in a case study of a phosphate fertilizer industry is applied, assessing occupational exposure to ionizing radiation caused by external radiation and the inhalation of radioactive gases and dust.
- Naturally occurring radioactive materials: a method for assessing the risk of exposurePublication . Estevez, J. G.; Nunes, FernandoNaturally Occurring Radioactive Materials (NORM) are materials that are found naturally in the environment and contain radioactive isotopes that can cause negative effects on the health of workers who manipulate them. Present in underground work like mining and tunnel construction in granite zones, these materials are difficult to identify and characterize without appropriate equipment for risk evaluation. The assessing methods were exemplified with a case study applied to the handling and processing of phosphoric rock where one found significant amounts of radioactive isotopes and consequently elevated radon concentrations in enclosed spaces containing these materials. © 2015 Taylor & Francis Group, London.
- Generation of Nakagami correlated fading in GNSS signals affected by ionospheric scintillationPublication . Nunes, Fernando; Sousa, FernandoWe propose a low complexity technique to generate amplitude correlated time-series with Nakagami-m distribution and phase correlated Gaussian-distributed time-series, which is useful for the simulation of ionospheric scintillation effects in GNSS signals. To generate a complex scintillation process, the technique requires solely the knowledge of parameters Sa (scintillation index) and σφ (phase standard deviation) besides the definition of models for the amplitude and phase power spectra. The concatenation of two nonlinear memoryless transformations is used to produce a Nakagami-distributed amplitude signal from a Gaussian autoregressive process.
- Characterization and performance analysis of a VDFLL GNSS receiver architecturePublication . Sousa, Fernando; Nunes, FernandoA non-coherent vector delay/frequency-locked loop architecture for GNSS receivers is proposed. Two dynamics models are considered: PV (position and velocity) and PVA (position, velocity, and acceleration). In contrast with other vector architectures, the proposed approach does not require the estimation of signals amplitudes. Only coarse estimates of the carrier-to-noise ratios are necessary.
- Risk Assessment of Chronic Exposure to Magnetic Fields near Electrical ApparatusPublication . Nunes, Fernando; Margato, ElmanoThe paper presents a numerical model to calculate ELF magnetic fields for typical conductor arrangements of electrical power lines. After a presentation of the several sources of the magnetic field and an introduction to the problems arising from the continued exposure of human beings to low frequency magnetic fields, a description of the numerical model for the magnetic field evaluation is presented, discussing its application. The attention is then devoted to the analysis of possible solutions for magnetic field reduction.
- Performance of a VDFLL GNSS receiver architecture in presence of interferencePublication . Sousa, Fernando; Nunes, FernandoWe discuss the advantages of using a vector delay/frequency-locked loop (VDFLL) architecture for GNSS receivers operating in scenarios disturbed by radio-frequency interference. Narrowband (sinusoidal) and wideband (chirp) interference signals are considered in the analysis. The VDFLL is constituted by a bank of code and frequency discriminators feeding a central extended Kalman filter that estimates the receiver's position, velocity, and clock bias. Simulation results are obtained using sine-phase binary offset carrier BOCs(1,1) modulation. The results are compared with the theoretical performance determined by the effective signal power to noise density ratio.
- Gnss blind interference detection based on fourth-order autocumulantsPublication . Nunes, Fernando; Sousa, FernandoGNSS signals affected by additive channel noise are approximately Gaussian, but often the presence of interference may change that distribution.We propose a blind detection method based on the Giannakis-Tsatsanis Gaussianity test to evaluate the presence of narrowband and wideband non-Gaussian interference. This method, resorting to the sample fourth-order autocumulants, is compared to other Gaussianity tests. The asymptotic covariance matrix of the estimated autocumulant vector is analytically determined, thus reducing the complexity of the proposed technique.
- Application of a configurable model for risk assessment in the work sitesPublication . Nunes, FernandoThis paper presents a configurable model for occupational risk analysis, supported in decision matrix risk assessment with variable indexes dimensions and weightings. The formulation proposed seeks to overcome typical limitations such as range compression effect, mistakenly over classification of smaller risks and subjective input information. Also it allows its customization for each type of risk as a function of input information available in order to minimize subjectivity, while normalizing output for the calculated risk levels with a percent scale. This approach facilitates the implementation of models built to go along with the life of installations with periodically updates to fulfill accumulated data. To avoid discontinuation of procedures and practices implemented in the organizations, the model also enables the easy incorporation of risk assessment and control procedures based on risk classification matrixes, already in use regardless of their size and sector of activity.
- Practical simulation of GNSS signals in the presence of ionospheric scintillatonPublication . Nunes, Fernando; Sousa, FernandoWe propose a low complexity technique to generate amplitude correlated time-series with Nakagami-m distribution and phase correlated Gaussian-distributed time-series, which is useful in the simulation of ionospheric scintillation effects during the transmission of GNSS signals. The method requires only the knowledge of parameters S4 (scintillation index) and σΦ (phase standard deviation) besides the definition of models for the amplitude and phase power spectra. The Zhang algorithm is used to produce Nakagami-distributed signals from a set of Gaussian autoregressive processes.