Properties Of White Noise Research Articles

A Robust Adaptive Dimension Reduction Technique With Application to Array Processing

We develop a data-adaptive dimension reduction algorithm that is robust against out-of-sector sources in application to array processing. The dimension reduction is done as a linear transformation (matrix filter). The matrix filter is designed adaptively such that the signal power within a certain sector is preserved while the out-of-sector power is maximally rejected. The columns of the beamspace matrix are designed sequentially, one column at a time. This sequential implementation is carried out by imposing orthogonality constraints between beamspace matrix columns. Hence, the white noise property at the output of the beamspace preprocessor is preserved. The latter is important for subsequent data processing. The proposed algorithm is computationally less expensive as compared to the existing data-adaptive beamspace design techniques. Simulation results validate the robustness of the developed algorithm, and they show its effectiveness and superiority to the existing algorithms.

Light-reflection random-target method for measurement of the modulation transfer function of a digital video-camera

This article reports the suggestion, realization and verification of the newly developed measuring means of the noiseless and locally shift-invariant modulation transfer function (MTF) of a digital video camera in a usual incoherent visible region of optical intensity, especially of its combined imaging, detection, sampling and digitizing steps which are influenced by the additive and spatially discrete photodetector, aliasing and quantization noises. Such means relates to the still camera automatic working regime and static two-dimensional spatially continuous light-reflection random target of white-noise property. The introduced theoretical reason for such a random-target method is also performed under exploitation of the proposed simulation model of the linear optical intensity response and possibility to express the resultant MTF by a normalized and smoothed rate of the ascertainable output and input power spectral densities. The random-target and resultant image-data were obtained and processed by means of a processing and evaluational PC with computation programs developed on the basis of MATLAB 6.5. The present examples of results and other obtained results of the performed measurements demonstrate the sufficient repeatability and acceptability of the described method for comparative evaluations of the performance of digital video cameras under various conditions.

Denoising of partial discharge signals in wavelet packets domain

Despite advances in the filtering techniques of partial discharge (PD) signals, an acceptable signal to noise ratio (SNR) remains elusive due to the presence of environmental noises. A wavelet packet transform-based method is proposed for effective denoising of on-site partial discharge data from a power generator and a gas-insulated substation. Taking advantage of the statistical properties of white noise, the method uses variance as the criterion to select the best tree. It is shown by comparative studies that the method restores the PD pulse from data with very low SNR. The denoised PD pulses enable more accurate diagnosis of insulation defects in HV equipment.

Detection and classification of power quality disturbances in noisy conditions

An approach to detect, localise and classify various types of power quality disturbances in noisy conditions is proposed. The approach is based on the statistical properties of white noise. The first step is to extract a given disturbance from the original signal including the white noise. After that, a short-time correlation algorithm is applied to limit the effect of white noise on wavelet analysis. In order to enhance the detection outcome, squared transform coefficients of the analysed power signal are used. Results related to common disturbances in electrical power quality analysis have shown the effectiveness and the feasibility of the proposed approach.

Noise properties of an YBCO SQUID

We have measured the electrical and the white noise properties of a high- T c SQUID at 65 K, using a room temperature low noise amplifier and a high- T c SQUID-based voltage amplifier. Operating at 65 K, the voltage amplifier had a voltage noise of 50 pV/ Hz , a current noise of 15 pA/ Hz and a 3 dB bandwidth of 300 kHz. We have found that the measured white voltage noise exceeded the theoretically expected noise by a factor of 2.

Inductance matching of high- TC dc-SQUIDs in planar gradiometers using a laser patterning technique

The inductance of the dc-SQUID in a planar galvanically coupled gradiometer of YBa 2Cu 3O 7− x was changed by lengthening the SQUID loop with a focused laser beam. The dc-SQUID inductance was increased from 50 pH to values close to 300 pH by this technique. This increased SQUID inductance changed the effective area of the gradiometer device as well as the SQUID parameter β L. We focused our investigations on the change of the peak-to-peak voltage of the SQUID modulation, on the change of the white noise properties as well as on the change in low frequency noise depending on an effective area and SQUID parameter β L. Different fixed critical currents of the dc-SQUID were considered in order to determine their influence on SQUID operation. For critical currents below 200 μA, a maximum of the white field gradient resolution could be achieved for corresponding SQUID parameters β L between 1.5 and 6 with 340 fT/(cm Hz 1/2) as the lowest noise level. Here, the necessity of a high I C R N product, an optimum critical current and an optimum dc-SQUID inductance was shown in order to realize a high device sensitivity. The influence of the grain boundary angle to achieve a high field gradient resolution even in unshielded environment as well as the combination of the increase of SQUID inductance with an additional ion beam etching technique for critical current reduction is considered.

Noise source and noise spectrum of perpendicular recording media

A noise source model based on small reversed domain structure was proposed for perpendicular recording media. The model indicates that a higher SQ ⊥ along with a smaller reversed domain size is effective in reducing the medium noise, and the intrinsic medium noise spectrum has a white noise property. The intrinsic noise spectrum obtained by the experiment for Co–Cr-based perpendicular recording media exhibited a white noise property agreeing with the model. While the medium noise for a longitudinal recording medium exhibited a colored spectrum with a broad peak at a low frequency. The white noise property indicates high recording resolution property of the perpendicular recording media.

Inductance dependence of noise properties of a high-T c dc superconducting quantum interference device

Properties of white noise of a high-Tc dc superconducting quantum interference device (SQUID) have been studied using numerical simulation. It is shown that thermal noise at T=77 K significantly affects the noise properties of the SQUID. As a result, dependencies of noise properties on inductance become quite different from conventional results at T=4.2 K. In contrast to the case T=4.2 K, the voltage noise of the SQUID at T=77 K depends very weakly on the inductance, while the transfer function degrades rapidly with inductance. Consequently, rapid degradation of flux noise with inductance, as compared with the case T=4.2 K, is caused mainly by that of the transfer function. These simulation results explain reasonably experimental results reported recently. Therefore, it is necessary to improve the transfer function for the improvement of noise properties in the case of large inductances. Numerical simulation shows that a method for improving the transfer function using resistively shunted inductance or three Josephson junctions, which was proposed by the authors, is also useful for improving noise properties in the case of large inductances.

PERIODIC CORRELATION IN STRATOSPHERIC OZONE DATA

Abstract. A 50‐year time series of monthly stratospheric ozone readings from Arosa, Switzerland, is analyzed. The time series exhibits the properties of a periodically correlated (PC) random sequence with annual periodicities. Spectral properties of PC random sequences are reviewed and a test to detect periodic correlation is presented. An autoregressive moving‐average (ARMA) model with periodically varying coefficients (PARMA) is fitted to the data in two stages. First, a periodic autoregressive model is fitted to the data. This fit yields residuals that are stationary but non‐white. Next, a stationary ARMA model is fitted to the residuals and the two models are combined to produce a larger model for the data. The combined model is shown to be a PARMA model and yields residuals that have the correlation properties of white noise.

Signal and white noise properties of edge junction dc SQUID’s

We have fabricated and characterized the noise performance of submicron edge junction dc superconducting quantum interference devices (SQUID’s) which exhibit excellent signal properties and extremely high flux sensitivity. At frequencies above about 3 MHz, the SQUID noise is white and is in reasonable agreement with computer simulations for a thermal noise-limited detector. In one device the measured flux energy resolution is 1.6±0.5ℏ at 1.5 K, within a factor of 2 of the quantum-limited value suggested by theoretical modeling.

Objective Determination of the Noise Level in Doppler Spectra

A method is described for the objective determination of the noise level in Doppler spectra. The method makes use of the physical properties of white noise and is suitable for automatic computation. It is shown that the method produces reliable results when used in conjunction with the lower-bound method of estimating vertical air velocities.

Quantum Effects in Communications Systems

The information capacity of various communications systems is considered. Quantum effects are taken fully into account. The entropy of an electromagnetic wave having the quantum statistical properties of white noise in a single transmission mode is found, and from it the information efficiency of various possible systems may be derived. The receiving systems considered include amplifiers, heterodyne and homodyne converters and quantum counters. In the limit of high signal or noise power (compared to hνB, where h is Planck's constant and ν and B are, respectively, the center frequency and bandwidth of the channel) the information efficiency of an amplifier can approach unity. In the limit of low powers the amplifier becomes inefficient, while the efficiency of the quantum counter can approach unity. The amount of information that can be incorporated in a wave drops off rather rapidly when the power drops below hνB.