Signal Noise Suppression Research Articles

De-striping hyperspectral imagery using wavelet transform and adaptive frequency domain filtering

Hyperspectral imagers are built line-by-line similar to images acquired by pushbroom sensors. They can experience striping artifacts due to variations in detector response to incident imagery. In this research, a method for hyperspectral image de-striping based on wavelet analysis and adaptive Fourier zero-frequency amplitude normalization has been developed. The algorithm was tested against three other de-striping algorithms. Hyperspectral image bands of different scenes with significant striping and random noise, as well as an image with simulated noise, were used in the testing. The results were assessed visually and quantitatively using frequency domain Signal-to-Noise Ratio (SNR), Root Mean Square Error (RMSE) and/or Peak Signal-to-Ratio (PSNR). The results demonstrated the superiority of our proposed algorithm in de-striping hyperspectral images without introducing unwanted artifacts, yet preserving image details. In the noise-induced image results, the proposed method reduced RMSE error and improved PSNR by 3.5 dB which is better than other tested methods. A Combined method, integrating the proposed algorithm with a generic wavelet-based de-noising algorithm, showed significant random noise suppression in addition to stripe reduction with a PSNR value of 4.3 dB. These findings make the algorithm a candidate for practical implementation on remote sensing images including high resolution hyperspectral images contaminated with stripe and random noise.

All-Optical Regeneration Based on Phase-Sensitive Nondegenerate Four-Wave Mixing in Optical Fibers

An optical regeneration scheme based on nondegenerate phase-sensitive amplification in highly nonlinear fibers is numerically investigated. The proposed regenerator exhibits significant amplitude and phase noise suppression properties and eliminates the need for precise phase and frequency locking with the input return-to-zero differential phase-shift keying signal.

Integration of Bass Enhancement and Active Noise Control System in Automobile Cabin

With the advancement of digital signal processing technologies, consumers are more concerned with the quality of multimedia entertainment in automobiles. In order to meet this demand, an audio enhancement system is needed to improve bass reproduction and cancel engine noise in the cabins. This paper presents an integrated active noise control system that is based on frequency‐sampling filters to track and extract the bass information from the audio signal, and a multifrequency active noise equalizer to tune the low‐frequency engine harmonics to enhance the bass reproduction. In the noise cancellation mode, a maximum of 3 dB bass enhancement can be achieved with significant noise suppression, while higher bass enhancement can be achieved in the bass enhance mode. The results show that the proposed system is effective for solving both the bass audio reproduction and the noise control problems in automobile cabins.

Speech enhancement via Mel-scale Wiener filtering with a frequency-wise voice activity detector

This paper presents a speech enhancement system that enables a comfortable communication inside an automobile. A couple of novel concepts are proposed in an effort to improve two major building blocks in the existing speech enhancement systems: a voice activity detector (VAD) and a noise filtering algorithm. The proposed VAD classifies a given data frame as speech or noise at each frequency, enabling the frequency-wise updates of noise statistics and thereby improving the effectiveness of the noise filtering algorithms by providing more up-to-date noise statistics. The celebrated Wiener filter is adopted in this paper as the accompanying noise filtering algorithm, which results in significant noise suppression. Yet, the musical noise present in most Wiener filter-based systems prompts the idea of applying the Wiener filter in the Mel-scale in which the human auditory system responds to the external stimulation. It turns out that the Mel-scale Wiener filter creates some masking effects and thereby reduces musical noise significantly, leading to smooth transition between data frames.

Analysis and suppression of SSN noise coupling between power/ground plane cavities through cutouts in multilayer packages and PCBs

The authors introduced a model of simultaneous switching noise (SSN) coupling between the power/ground plane cavities through cutouts in high-speed and high-density multilayer pack-ages and printed circuit boards (PCBs). Usually, the cutouts are used in multilayer plane structures to isolate the SSN of noisy digital circuits from sensitive analog circuits or to provide multiple voltage levels. The noise-coupling model is expressed in terms of the transfer impedance. The proposed modeling and analysis results are compared with measured data up to 10 GHz to demonstrate the validity of the model. It is demonstrated that the cutout is the major gate for SSN coupling between the plane cavities, and that substantial SSN coupling occurs between the plane cavities through the cutout at the resonant frequencies of the plane cavities. The coupling mechanism and characteristics of the noise coupling, from which a method of suppression of the SSN coupling evaluated was also analyzed and discussed. Proper positioning of the cutout and the devices at each plane cavity achieves significant noise suppression at certain resonant frequencies. The suggested suppression method of the SSN coupling was successfully proved by frequency domain measurement and time domain analysis.

Fourier transform method for imaging atmospheric Cherenkov telescopes

We propose Fourier transform (hereafter FT) method for processing the images of extensive air showers (EAS) detected by imaging atmospheric Cherenkov telescopes (IACT) used in the very high energy (VHE) gamma-ray astronomy. The method uses a special type of discrete Fourier transforms (DFT) based on orbit functions of compact Lie groups, and the use of continuous extension of the inverse transform to approximate the discrete images by continuous EAS brightness distribution functions. Here we present the FT-method for SU(3) group which provides a practicable technique for realization of the DFT approach for functions sampled on hexagonal symmetry grids implemented in the current IACT cameras. We note that the proposed FT-method can also be implemented for the rectangular grids using the DFT on SU(2) × SU(2) group. To show the viability of the FT-method, here we apply it to Monte-Carlo simulated bank of TeV proton and gamma-ray EAS images only for the case of a stand-alone telescope and use a simple single-parameter (ALPHA) analysis. Comparing between the FT-method and the currently used ‘standard’ method for signal enhancement shows that a straightforward use of FT technique within standard parameterization scheme allows a better and systematic enhancement of the gamma-ray signal. The relative difference between these two methods becomes more profound especially for ‘photon poor’ images, for which the standard method significantly deteriorates. It suggests that the effective EAS detection thresholds could be reduced with implementation of the FT technique for IACTs. This prediction is further supported by a significant noise suppression capability of the method after using simple ‘low-pass’ filters in the image frequency domain. This new approach allows very deep ‘tail’ (and ‘height’) image cuts, differentiation of images, provides frequency spectra, etc., which could be used for development of new effective parameters for the EAS image processing.

Nonlinear sinogram smoothing for low-dose X-ray CT

When excessive quantum noise is present in extremely low dose X-ray CT imaging, statistical properties of the data has to be considered to achieve a satisfactory image reconstruction. Statistical iterative reconstruction with accurate modeling of the noise, rather than a filtered back-projection (FBP) with low-pass filtering, is one way to deal with the problem. Estimating a noise-free sinogram to satisfy the FBP reconstruction for the Radon transform is another way. The benefits of the latter include a higher computation efficiency, more uniform spatial resolution in the reconstructed image, and less modification of the current machine configurations. In a clinic X-ray CT system, the acquired raw data must be calibrated, in addition to the logarithmic transform, to achieve the high diagnostic image quality. The calibrated projection data or sinogram no longer follow a compound Poisson distribution in general, but are close to a Gaussian distribution with signal-dependent variance. In this paper, we first investigated a relatively accurate statistical model for the sinogram data, based on several phantom experiments. Then we developed a penalized likelihood method to smooth the sinogram, which led to a set of nonlinear equations that can be solved by iterated conditional mode (ICM) algorithm within a reasonable computing time. The method was applied to several experimental datasets acquired at 120 kVp, 10 mA/20 mA/50 mA protocols with a GE HiSpeed multi-slice detector CT scanner and demonstrated a significant noise suppression without noticeable sacrifice of the spatial resolution.

An adaptive microphone array using multiple fictitious sources

AbstractThis paper proposes a method of carrying out stable sound acquisition even if the targeted sound source moves, by constraining the sensitivity of an adaptive microphone array using multiple fictitious sources. Although the adaptive microphone array can achieve significant noise suppression, the conventional one has a problem in that the desired sound degrades and the noise increases when the desired sound source moves. In our method, multiple fictitious sources are used to constrain the sensitivity to the sound acquisition range. This effect is confirmed by a simulation comparing the proposed method and conventional ones. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 87(2): 20–32, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.10131

Regenerative properties of a pump-modulated four-wave mixing scheme in dispersion-shifted fibers

A new scheme for all-optical signal reshaping is proposed. It is shown that proper adjustment of the operating conditions of a wavelength converter based on four-wave mixing (FWM) in dispersion-shifted fiber (DSF) results in significant extinction ratio enhancement and noise suppression of the converted signal. The key issue in the proposed idea is the application of the modulation bitstream on the input pump wave. Detailed numerical simulation shows that it is possible to achieve a wavelength-converted output with extinction ratio of 20 dB when the extinction ratio of the input signal is 10.5 dB, while at the same time, the improvement in the Q-factor is almost 6 (from 6.5 at the input, it becomes more than 12 at the output). The theoretical predictions have been experimentally confirmed by measuring the transfer function of the FWM in a 17-km-long DSF under different operating conditions. The obtained results are in a very good agreement with those predicted theoretically.

Noise suppressing transmitter and noise suppressing method

Signals outputted from microphones 111 and 112 are inputted through filters 118 and 119 to noise suppressing sections A and B. One having smaller power is selected from output signals S107a and S107b by switching a selection switch SW in a signal power comparing section 117, to which the output signals S107a and S107b have been inputted, and a transmission signal S108 level-adjusted by a level adjuster is outputted. In the noise suppressing section A (similarly in the section B), microphone output signals S102 and S103 are processed by an adder 113a and a subtracter 114a, a signal S105a outputted from the subtracter 114a is inputted to a subtracter 116a through a filter 115a having a transmission function Fa(z) decided by the positions of the microphones 111 and 112 and a noise suppression signal S107a obtained by subtracting the signal S105a from a signal S104a outputted from the adder 113a is outputted.

Microwave measurement of shot noise in resonant tunneling diodes

The room temperature shot noise of a resonant tunneling diode was determined from microwave measurements as a function of bias. An AlAs/GaAs structure with multiple quasibound well states and asymmetric barrier thicknesses was investigated over a bias regime exceeding the first resonance. In contrast to results for single well state devices, significant noise suppression below the classical limit was also observed for bias ranges beyond the first resonance level. This suppression can be explained by competition between the first and second resonance levels for the thick barrier on the emitter side and due to predominately single barrier tunneling in the reverse polarity.

The atom-cavity system as a generator of quadrature squeezed states

This paper describes experiments with a coupled atom-cavity system generating quadrature squeezed states of light. A wide range of parameters was explored and a regime was found where a beam of laser light with significant power (0.17 mW) and good noise suppression (measured 18±3%, inferred 50±10%) was observed. An analysis of the exact phase of the noise suppression shows it to be a minimum uncertainty state with reduced noise in a combined amplitude/phase quadrature. The observations are in good qualitative agreement with a full quantum theory of squeezing in optical bistability.

Analytical model of shot noise in double-barrier resonant-tunneling diodes

The shot noise in double-barrier diodes is analyzed using the stationary-state approach to resonant tunneling through the first quasi-bound level. Significant deviations from full shot noise are predicted. Significant shot noise suppression occurs in the entire positive differential resistance region below the current peak, and shot noise enhancement occurs in the negative differential resistance region above the peak. The physical basis for these effects is assumed to be the modulation of the double-barrier transmission probability by charge stored in the first quasi-bound level in the quantum well. The analysis confirms microwave noise measurements of high-speed double-barrier diodes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A double-stage injection-locked oscillator for optically fed phased array antennas

In an optically fed phased array antenna system, the microwave carrier signal is transmitted via a modulated lightwave to each active T/R (transmit/receive) module, where it must be converted back to the microwave domain. Currently, efficient optical-to-microwave conversion is extremely difficult, as the detected microwave signal is weak and noisy. A novel circuit, containing a high-gain/low-noise microwave injection-locked oscillator, has been developed to improve the interface between the optical and microwave components. The circuit utilizes two FETs and a dielectric resonator, which serves as a frequency-dependent feedback element. The circuit, designed to operate at about 8 GHz, provides significant amplitude and phase noise suppression. In addition, the circuit realization is compatible with MMIC technology.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new noise suppression method for high-definition CCD cameras

A novel noise suppression method for a high-definition CCD (charge coupled device) camera, the RDS (reflection-delayed noise suppression) method, is described. By using the reflection in a delay line, it has become possible to obtain both significant noise suppression and a wide frequency bandwidth. The method is superior to conventional methods in that its frequency bandwidth is very wide and its high-speed operations are very stable. The performance of a HDTV (high-definition TV) three-CCD color camera using this method is reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>