Standard Deviation Of Phase Difference Research Articles

Device-Free Human Activity Recognition Based on GMM-HMM Using Channel State Information

This paper presents a machine learning method, Gaussian Mixture Hidden Markov Model (GMM-HMM), for device-free activity recognition using WiFi channel state information (CSI). The basic concept of CSI is introduced and signal changes caused by human activity are described, which demonstrates that human activity can be identified using a unique mapping between action and signal variations. The phase difference expanded matrix is built by the mean and standard deviation of phase difference as feature matrix after linear correction and Savitzky-Golay filter is performed on the CSI raw phase information. The GMM-HMM is used for classification as the human activity can be modeled as the Markov process and the complex activity patterns can be fitted by multiple Gaussian density functions, respectively. The proposed system is verified on the self-collected datasets and several factors affecting the recognition accuracy are analyzed. Furthermore, the system has compared with the previous work. High accuracy and robustness in universal scenarios are realized. Experimental results show that the average recognition accuracy of the proposed system is over 97%.

3-D Hemorrhage Imaging by Cambered Magnetic Induction Tomography

Magnetic induction tomography (MIT) is a promising imaging technique for hemorrhage detection due to the features of initial diagnosis and continuous monitoring. The dispersed nature of the electromagnetic field makes the MIT difficult to image the intraaxial hemorrhage. An open cambered MIT was proposed to improve the sensitivity of extraaxial hemorrhage which is located 14–20 mm below the scalp. Realistic head models with different hemorrhage volumes and positions are used for simulation. The imaging performance of the cambered MIT is compared with the cylindrical MIT based on the time-difference and frequency-difference imaging methods, respectively. Different levels of noise (standard deviation of phase difference at 0.5 and 0.75 m°) were added to the phase difference measurements of time difference at 1 MHz. 3-D images were reconstructed by the single-step Tikhonov regularization method. Two factors of correlation coefficient $r_{\mathrm{ pd}}$ and localization error $L_{e}$ are introduced to assess the quality of the images. The results show that the cambered MIT obtains a better imaging performance of extraaxial hemorrhage than cylindrical MIT. In particular, for the hemorrhage of 7 mL at the lower position by time-difference imaging, $r_{\mathrm{ pd}}$ of the cambered MIT is increased by 42.3% and $L_{e}$ is reduced by 37.7% relative to the cylindrical MIT. The cambered MIT obtained twice the signal-to-noise ratio of phase difference for the frequency-difference method than the cylindrical MIT. The cambered MIT improves the sensitivity of near-subsurface locations, which provides a high resolution and portable way to monitor the extraaxial hemorrhage.

Performance Evaluation of Azimuth Offset Method for Mitigating the Ionospheric Effect on SAR Interferometry

Synthetic aperture radar (SAR) signals interact with the ionosphere layer when they propagate through the atmosphere, leading to the phase delay error for SAR interferometry (InSAR). To mitigate this error for SAR interferometry, azimuth offset method is proposed. However, the performance of it has not been fully investigated. In this situation, this study makes a comprehensive performance analysis of azimuth offset method through processing the simulated and real SAR data. The experimental result indicates that this method can effectively mitigate the ionospheric phase delay error, where the standard deviation of phase difference after correction (2.6 rad.) decreased by almost 2 times, compared to those before correction (5.3 rad.) for the real SAR data. However, it is also found that the method is affected by the random noise, which may induce the improper estimation of integral constants and consequently affect the ionospheric correction. Moreover, the severe deformation signals in the interferogram may lead to the estimation error of integral constants and scaling factor. Therefore, it should mask out the deformation signals when using the azimuth offsets method to correct the ionospheric error. This study may provide useful information when using azimuth offset method to mitigate the ionospheric phase delay error on InSAR.

Object localization using the statistical behavior of volume speckle fields

Speckle noise presents challenges in object localization using reconstructed wavefronts. Here, a technique for axial localization of rough test objects based on a statistical algorithm that processes volume speckle fields is demonstrated numerically and experimentally. The algorithm utilizes the standard deviation of phase difference maps as a metric to characterize the object wavefront at different axial locations. Compared with an amplitude-based localization method utilizing energy of image gradient, the technique is shown to be robust against speckle noise.

Estimation of Damping Correction Factors Using Duration Defined by the Standard Deviation of Phase Difference

The damping correction factors (DCFs) to convert the 5% damping acceleration response spectra to those for other damping levels are computed for the records of 13 Japanese earthquakes. Their correlation with the standard deviation of phase difference ( σ) is also investigated in ten frequency bands. The σ-DCF relations obtained are found to be very similar across the different types of earthquakes. Further, regression analysis suggests that for damping ratios of 1% and 2%, with the increase in σ, the DCFs increase in low-frequency bands (up to 4–5 Hz), whereas they decrease in higher frequency bands. On the other hand, for damping ratios of more than 5%, with the increase in σ, the DCFs decrease in low-frequency bands (up to 1 Hz), whereas the opposite tendency is observed in higher frequency ranges. This research also discusses the applicability of the σ-DCF relations to design ground motion simulation.

The effect of phase stabilization of microwave oscillations in nanosecond Gunn oscillators

The effect of the semiconductor structure of an oscillator diode on the phase stabilization of microwave oscillations in a nanosecond Gunn oscillator by using a modulating voltage pulse edge is investigated. Numerical simulation is employed to determine phase deviations depending on the scatter of pulseedge duration and pulse amplitude. The standard deviation of phase-delay time of microwave oscillations in the oscillator with regard to a constant level at the modulating pulse edge and the standard deviation of phase difference of microwave oscillations in two electrodynamically insulated oscillators connected in parallel to one and the same modulator have been measured.

Efficient approach for three-dimensional shape measurement using fringe projection by complex coefficient FIR band-pass filter

An efficient approach for three-dimensional (3D) shape measurement is proposed. Phase distribution is obtained directly by filtering deformed fringe pattern with complex coefficient finite impulse response (FIR) band-pass filter. Firstly, a FIR low-pass filter is designed; its bandwidth is half of that of the deformed fringe pattern. Secondly, the complex coefficient FIR band-pass filter is gained by moving the frequency spectrum of low-pass filter to the position where the frequency spectrum of deformed fringe pattern located. Finally, the phase distribution is obtained by filtering the deformed fringe pattern with designed filter and calculating the argument of the filtered pattern. The experimental results reveal that a high resolution 3D image with texture can be obtained. Compared with conventional Fourier transform profilometry (FTP), the standard deviation of phase difference between these two methods reaches only 0.75%. As a result, this approach provides a new way to obtain phase distribution of deformed fringe pattern in spatial domain instead spatial frequency domain.

Studies on the statistical properties of phase difference of speckle fields

According to the relations between the phase and the complex speckle amplitude, a phase angle is constructed to estimate the free standard deviation of phase difference of speckle fields. The relative accurate amending expression of evaluating the free standard deviation of phase difference is derived for the Gaussian speckle fields. The statistical properties of phase difference are studied for the Gaussian speckle fields of diffraction fields. The theoretical values of the free standard deviation of phase difference for the case of fully developed speckle fields are compared with the numerical values of the free standard deviation which are calculated from the Gaussian theory of the fully developed speckle fields.

Theoretical study on the statistical properties of phase difference between two interfering speckle fields

The statistical properties of phase difference between two interfering speckle fields are studied theoretically with the general expression of the free standard deviation of the phase difference of speckle fields. The experimental results of the standard deviations of phase difference between two interfering partially developed speckle fields in the diffractive region [Opt. Quantum Electron. 19 (1987) 59] are studied and discussed theoretically with the general expression of the free standard deviation of phase difference of speckle fields. The theoretical standard deviations of phase difference for the case of two interfering fully developed Gaussian speckle fields are compared with that which are numerically calculated from the Gaussian theory.