Search results for "Frequency analysis"

Regional frequency analysis of extreme rainfall in Sicily (Italy)

2018

Artifacts and Errors in Cross-Spectrum Phase Noise Measurements : Invited lecture

2021

Inserting an attenuator between the oscillator under test and the phase noise analyzer, one expects that the white phase noise increases monotonically with the attenuation. By contrast, we observe that with some oscillators the white noise has sharp minimum for a given value of the attenuation, which clearly indicates problem. With other oscillators, it increases monotonically with the attenuation, but the values are not consistent with the thermal energy introduced by the attenuator. In both cases artifacts are present, which takes the form of a sharp notch in the spectrum, occurring where the white FM noise crosses the white PM noise. Such anomalous behavior is the tip of the iceberg, and…

Detection of steering direction using EEG recordings based on sample entropy and time-frequency analysis.

2016

Monitoring driver's intentions beforehand is an ambitious aim, which will bring a huge impact on the society by preventing traffic accidents. Hence, in this preliminary study we recorded high resolution electroencephalography (EEG) from 5 subjects while driving a car under real conditions along with an accelerometer which detects the onset of steering. Two sensor-level analyses, sample entropy and time-frequency analysis, have been implemented to observe the dynamics before the onset of steering. Thus, in order to classify the steering direction we applied a machine learning algorithm consisting of: dimensionality reduction and classification using principal-component-analysis (PCA) and sup…

Ability of short-time Fourier transform method to detect transient changes in vagal effects on hearts: a pharmacological blocking study.

2006

Conventional spectral analyses of heart rate variability (HRV) have been limited to stationary signals and have not allowed the obtainment of information during transient autonomic cardiac responses. In the present study, we evaluated the ability of the short-time Fourier transform (STFT) method to detect transient changes in vagal effects on the heart. We derived high-frequency power (HFP, 0.20–0.40 Hz) as a function of time during active orthostatic task (AOT) from the sitting to standing posture before and after selective vagal (atropine sulfate 0.04 mg/kg) and sympathetic (metoprolol 0.20 mg/kg) blockades. The HFP minimum point during the first 30 s after standing up was calculated and…

A new Framework for the Spectral Information Decomposition of Multivariate Gaussian Processes

2021

: Different information-theoretic measures are available in the literature for the study of pairwise and higher-order interactions in multivariate dynamical systems. While these measures operate in the time domain, several physiological and non-physiological systems exhibit a rich oscillatory content that is typically analyzed in the frequency domain through spectral and cross-spectral approaches. For Gaussian systems, the relation between information and spectral measures has been established considering coupling and causality measures, but not for higher-order interactions. To fill this gap, in this work we introduce an information-theoretic framework in the frequency domain to quantify t…

Spectrogram Analysis of Multipath Fading Channels under Variations of the Mobile Speed

2016

When modelling, analysing, and simulating mobile radio channels, it is generally assumed that the speed of the mobile station (MS) is constant. In practice, however, the mobile speed varies with time. Mobile speed variations result in nonwide- sense stationary multipath fading channels, which can be modelled by a sum-of-chirps (SOCh) processes. In this paper, we analyse the local Doppler power spectral density (PSD) of SOCh processes by using the concept of the spectrogram. The spectrogram provides an estimate of the local Doppler PSD and gives insight into how the Doppler PSD changes over time if the MS increases or decreases its speed. A closed-form solution is presented for the spectrogr…

Enriqueciendo la investigación en humanidades digitales. Análisis de textos de claustros académicos de la Universidad de Valencia (1775-1779) con KH …

2020

[ES] La aplicación de métodos automatizados en cualquier investigación ha facilitado el trasvase de metodologías de una disciplina a otra, permitiendo realizar análisis cuantitativos a textos con estructura o semiestructurados. El objeto de este trabajo es aplicar a un dataset en lenguaje natural -castellano del siglo XVIII- métodos de análisis de la disciplina de documentación. Pretende establecer una metodología automática de análisis cuantitativo y cualitativo de textos, que permita enriquecer en el futuro las conclusiones procedentes del análisis histórico tradicional. Este estudio construye los procedimientos necesarios para poder aplicar análisis de frecuencia, extracción y clasificac…

Enhancing the Resolution of the Spectrogram of Non-Stationary Mobile Radio Channels by Using Massive MIMO Techniques

2017

This paper is concerned with the enhancement of the resolution of the spectrogram of non-stationary mobile radio channels using massive multiple-input multiple-output (MIMO) techniques. By starting from a new generic geometrical model for a non-stationary MIMO channel, we derive the complex MIMO channel gains under the assumption that the mobile station (MS) moves with time-variant speed. Closed-form solutions are derived for the spectrogram of the complex MIMO channel gains by using a Gaussian window. It is shown that the window spread can be optimized subject to the MS's speed change. Furthermore, it is shown that the spectrogram can be split into an auto-term and a cross-term. The auto-t…

Estimation of the Velocity of a Walking Person in Indoor Environments from mmWave Signals

2018

The present work is motivated by the growing interest in using millimeter-wave (mmWave) bands in future wireless indoor communications. For a variety of wireless indoor applications, such as remote medical care, healthcare services, and human-machine interaction, it is of crucial importance to estimate the velocity of walking persons in indoor environments with high precision. In this paper, we present a novel procedure for estimating the velocity of a walking person in indoor environments by using mmWave signals. The indoor environment is considered to be equipped with a distributed $2\times 2$ multiple-input multiple-output (MIMO) system operating in the 60 GHz band. The proposed approach…

ERP qualification exploiting waveform, spectral and time-frequency infomax

2008

The present contribution briefly introduces an event related potential (ERP) detector. The specified detector includes three kinds of features of ERP. They are the ERP waveform feature, ERP spectral feature and ERP time-frequency feature respectively. According to these characteristics, two parameters are defined to reflect the timing feature of ERP. The mismatch negativity (MMN) is taken as the example to design an exact qualification detector. The experiment validates that the computer can automatically detect the raw trace to reflect the quality of the dataset, qualify the filtered trace to test whether the artifacts have been filtered out, and select the ERP-like component to reject art…