Showing papers on "Noise measurement published in 1992"

Estimation of fractal signals from noisy measurements using wavelets

Abstract: The role of the wavelet transformation as a whitening filter for 1/f processes is exploited to address problems of parameter and signal estimations for 1/f processes embedded in white background noise. Robust, computationally efficient, and consistent iterative parameter estimation algorithms are derived based on the method of maximum likelihood, and Cramer-Rao bounds are obtained. Included among these algorithms are optimal fractal dimension estimators for noisy data. Algorithms for obtaining Bayesian minimum-mean-square signal estimates are also derived together with an explicit formula for the resulting error. These smoothing algorithms find application in signal enhancement and restoration. The parameter estimation algorithms find application in signal enhancement and restoration. The parameter estimation algorithms, in addition to solving the spectrum estimation problem and to providing parameters for the smoothing process, are useful in problems of signal detection and classification. Results from simulations are presented to demonstrated the viability of the algorithms. >

Using additive noise in back-propagation training

Abstract: The possibility of improving the generalization capability of a neural network by introducing additive noise to the training samples is discussed. The network considered is a feedforward layered neural network trained with the back-propagation algorithm. Back-propagation training is viewed as nonlinear least-squares regression and the additive noise is interpreted as generating a kernel estimate of the probability density that describes the training vector distribution. Two specific application types are considered: pattern classifier networks and estimation of a nonstochastic mapping from data corrupted by measurement errors. It is not proved that the introduction of additive noise to the training vectors always improves network generalization. However, the analysis suggests mathematically justified rules for choosing the characteristics of noise if additive noise is used in training. Results of mathematical statistics are used to establish various asymptotic consistency results for the proposed method. Numerical simulations support the applicability of the training method. >

Radiometric detection of spread-spectrum signals in noise of uncertain power

Abstract: The standard analysis of the radiometric detectability of a spread-spectrum signal assumes a background of stationary, white Gaussian noise whose power spectral density can be measured very accurately. This assumption yields a fairly high probability of interception, even for signals of short duration. By explicitly considering the effect of uncertain knowledge of the noise power density, it is demonstrated that detection of these signals by a wideband radiometer can be considerably more difficult in practice than is indicated by the standard result. Worst-case performance bounds are provided as a function of input signal-to-noise ratio (SNR), time-bandwidth (TW) product and peak-to-peak noise uncertainty. The results are illustrated graphically for a number of situations of interest. It is also shown that asymptotically, as the TW product becomes large, the SNR required for detection becomes a function of noise uncertainty only and is independent of the detection parameters and the observation interval. >

Wave techniques for noise modeling and measurement

Abstract: The noise wave approach is applied to analysis, modeling, and measurement applications. Methods are presented for the calculation of component and network noise wave correlation matrices. Embedding calculations, relations to two-port figures-of-merit, and transformations to traditional representations are discussed. Simple expressions are derived for MESFET and HEMT noise wave parameters based on a linear equivalent circuit. A noise wave measurement technique is presented and experimentally compared with the conventional method. >

Cross-correlation phase noise measurements

Abstract: The noise floor of a typical two channel phase noise measurement system is set by the phase detector and amplifiers that follow the detector. If the phase noise of two oscillators is measured using two of these test systems, the output noise of the equipment is uncorrelated except for the component that is due to the phase noise between the oscillators. Examination of a system which uses matched power splitters, two phase detectors, and post amplifiers reveals that an exceptionally low noise floor is achievable. The time required to reach a given percentage of precision in the measurement at these low noise floors is lengthened due to the need to average away the uncorrelated noise. The details of the setup, including calibration procedures and confidence intervals for the measurement, are discussed. >

A theoretical and experimental study of the noise behavior of subharmonically injection locked local oscillators

Abstract: A method for the phase-noise characterization of optically controlled subharmonically injection-locked oscillators that is based on a nonlinear model of synchronized oscillators is presented. It allows FM noise degradation at large-signal levels to be predicted easily and accurately. The theoretical analysis shows that (1) the nth-order subharmonic injection locking oscillator is primarily locked by the nth harmonic output of an injected signal, which is generated by the nonlinearity of the active device; (2) the minimum FM noise degradation factor of the nth-order subharmonically locked oscillator is n/sup 2/ when the injection power is sufficiently strong; and (3) a subharmonic injection locking LO with low injection power, good FM noise degradation, and large locking range can be designed by determining the optimum injection power level, by selecting the optimal nonlinear multiplication factor, and by decreasing the intrinsic noise level of the active device. The experimental results confirm the accuracy of the analysis. >

Noise resistant auditory model for parametrization of speech

Abstract: A method and system are provided for alleviating the harmful effects of convolutional and additive noise in speech, such as due to the environmental noise and linear spectral modification, based on the filtering of time trajectories of an auditory-like spectrum in a particular spectral domain.

A general noise de-embedding procedure for packaged two-port linear active devices

Abstract: A method based on the noise correlation technique and its applications is described. The package, which need not be reciprocal, may consist of an arbitrary interconnection of linear passive elements at thermal equilibrium. Only the terminal admittance properties of the package need be known. However, in certain special cases which lead to singular submatrices of the admittance matrix, the method is inapplicable. This situation can occur when elements such as isolators are part of the package. The necessary theoretical foundation and experimental techniques to enable workers not familiar with the field to assemble the software and laboratory setup for two-port noise de-embedding is provided. The automated noise measurement system used for data acquisition and the mathematical basis for it are described in some detail. The validity of the de-embedding approach is established with extensive experimental data obtained on three MESFETs and a pseudomorphic HEMT. >

Extracting thresholds from noisy psychophysical data

Abstract: Psychophysical studies with infants or with patients often are unable to use pilot data, training, or large numbers of trials. To evaluate threshold estimates under these conditions, computer simulations of experiments with small numbers of trials were performed by using psychometric functions based on a model of two types of noise: stimulus-related noise (affecting slope) and extraneous noise (affecting upper asymptote). Threshold estimates were biased and imprecise when extraneous noise was high, as were the estimates of extraneous noise. Strategies were developed for rejecting data sets as too noisy for unbiased and precise threshold estimation; these strategies were most successful when extraneous noise was low for most of the data sets. An analysis of 1,026 data sets from visual function tests of infants and toddlers showed that extraneous noise is often considerable, that experimental paradigms can be developed that minimize extraneous noise, and that data analysis that does not consider the effects of extraneous noise may underestimate test-retest reliability and overestimate interocular differences.

Low-frequency noise properties of N-p-n AlGaAs/GaAs heterojunction bipolar transistors

Abstract: The low-frequency noise characteristics of N-p-n Al/sub x/Ga/sub 1-x/As/GaAs heterojunction bipolar transistors (HBTs) have been investigated as a function of bias current, device geometry, extrinsic-base-surface condition, Al mole fraction in the emitter, and temperature in order to identify the dominant noise mechanisms. These measurements show the existence of three distinct regions in the noise spectra: a 1/f noise line shape, a Lorentzian spectrum (noise 'bump'), and a white-noise region. The 1/f noise is attributed to fluctuations in the extrinsic-base surface recombination current. The noise bump is generated by an AlGaAs trap in the emitter-base junction. The DX center was identified as a possible candidate for this trap. It is shown that for 4- mu m*10- mu m emitter AlGaAs/GaAs HBTs, the use of a depleted, AlGaAs passivation ledge over the extrinsic-base surface typically reduced the 1/f base noise current by a factor of 10, and the reduction of the Al mole fraction from 0.3 to 0.2 decreased the magnitude of the noise bump by a factor of 3. >

3D relative position and orientation estimation using Kalman filter for robot control

Abstract: A vision-based position sensing system which provides three-dimensional relative position and orientation (pose) of an arbitrary moving object with respect to a camera for a real-time tracking control is studied. Kalman filtering was applied to vision measurements for the implicit solution of the photogrametric equations and to provide significant temporal filtering of the resulting motion parameters resulting in optimal pose estimation. Both computer simulation and real-time experimental results are presented to verify the effectiveness of the Kalman filter approach with large vision measurement noise. >

A new adaptive noise cancellation scheme in the presence of crosstalk (speech signals)

Abstract: The application of adaptive filters in noise canceling often requires the relative placement of the two transducers at a distance that necessitates a larger order filter in order to obtain an adequate output signal-to-noise ratio. A new adaptive filter structure is introduced that permits a closer placement of the transducers and that allows the cancellation of noise in the presence of crosstalk. Algorithms are developed for the new transversal and lattice filter estimators. Simulations show considerable improvement in mean-square error over that obtained with standard noise canceling algorithms. >

Active noise eliminating system

Abstract: An active noise eliminating system comprises microphones for detecting residual noise, speakers for generating noise elimination sound for interference with the residual noise, a noise generating condition sensor for generating noise condition, a controller for generating noise elimination signals inputted to the speakers and determined by the detected residual noise signals and the detected noise condition signal in accordance with a control algorithm including transfer functions between the speakers and microphones respectively. The transfer functions are updated on the basis of a test signal generated when noise sound diverges.

Comfort noise generation for digital communication systems

Abstract: A digital discontinuous cellular communication system has a transmitter that transmits two frames of data following detection of voice inactivity. A receiver includes a comfort noise generator that uses the two frames of data to output noise to the speaker during period of voice inactivity. The comfort noise generator includes synthesis codebook with samples scaled by actual background noise and excitation codebook with samples filtered and scaled by the background noise that are combined to produce comfort noise having attributes and loudness level of the received background noise prior to interruption of transmission. The scaled signals are weighted to vary the loudness level and spectral attributes.

High-performance in W-band monolithic pseudomorphic InGaAs HEMT LNA's and design/analysis methodology

Abstract: High-performance W-band monolithic one- and two-stage low noise amplifiers (LNAs) based on pseudomorphic InGaAs-GaAs HEMT devices have been developed. The one-stage amplifier has a measured noise figure of 5.1 dB with an associated gain of 7 dB from 92 to 95 GHz, and the two-stage amplifier has a measured small signal gain of 13.3 dB at 94 GHz and 17 dB at 89 GHz with a noise figure of 5.5 dB from 91 to 95 GHz. An eight-stage LNA built by cascading four of these monolithic two-stage LNA chips demonstrates 49 dB gain and 6.5 dB noise figure at 94 GHz. A rigorous analysis procedure was incorporated in the design, including accurate active device modeling and full-wave EM analysis of passive structures. The first pass success of these LNA chip designs indicates the importance of a rigorous design/analysis methodology in millimeter-wave monolithic IC development. >

Microwave frequency discriminator with a cooled sapphire resonator for ultra-low phase noise

Abstract: First results are presented for an X-band frequency discriminator using a cooled sapphire microwave resonator. These results show a lower close-in (1-Hz-1-kHz offset) phase noise measurement floor than any oscillator presently available. This performance is made possible by a sapphire whispering-gallery mode resonator which shows the highest quality factor (with Q's up to 30 million) of any RF microwave, or acoustic resonator at temperatures to 77 K. Performance is increased by use of phase detection circuitry. The sapphire discriminator is used to characterize the phase noise of a single crystal quartz oscillator of the highest quality, without the use of a second similar oscillator as reference. >

Effects of Noise on Sensor Placement for On-Orbit Modal Identification of Large Space Structures

Abstract: A method of sensor placement for the purpose on-orbit modal identification and test-analysis correlation is presented. The method is an extension of the affective Independence method presented in past work to include the effects of a general representation of measurement noise. Sensor noise can be distributed nonuniformly throughout the structure as well as correlated between sensors. The only restriction is that the corresponding noise covariance intensity matrix is positive definite

Performance degradation of DOA estimators due to unknown noise fields

Abstract: A statistical performance analysis of subspace-based directions-of-arrival (DOA) estimation algorithms in the presence of correlated observation noise with unknown covariance is presented. The analysis of five different estimation algorithms is unified by a single expression for the mean-squared DOA estimation error which is derived using a subspace perturbation expansion. The analysis assumes that only a finite amount of array data is available. >

Zero-crossing based spectral analysis and SVD spectral analysis for formant frequency estimation in noise

Abstract: The authors discuss a method for spectral analysis of noise corrupted signals using statistical properties of the zero-crossing intervals. It is shown that an initial stage of filter-bank analysis is effective for achieving noise robustness. The technique is compared with currently popular spectral analysis techniques based on singular value decomposition and is found to provide generally better resolution and lower variance at low signal to noise ratios (SNRs). These techniques, along with three established methods and three variations of these method, are further evaluated for their effectiveness for formant frequency estimation of noise corrupted speech. The theoretical results predict and experimental results confirm that the zero-crossing method performs well for estimating low frequencies and hence for first formant frequency estimation in speech at high noise levels ( approximately 0 dB SNR). Otherwise, J.A. Cadzow's high performance method (1983) is found to be a close alternative for reliable spectral estimation. As expected the overall performance of all techniques is found to degrade for speech data. The standard autocorrelation-LPC method is found best for clean speech and all methods deteriorate roughly equally in noise. >

Detection of parallel discharges in gas insulated substations

Abstract: Four methods for partial discharge (PD) detection in gas-insulated substations were considered. Laboratory tests were carried out to determine the efficiency of these methods to detect defects and to discriminate among different defect types. The sensitivity of the methods is compared and the applicability of the methods in the field is discussed. In the laboratory the standard PD measuring method showed a good sensitivity to defects. In the field condition the standard PD measuring method can have a sensitivity much lower than in laboratory, due to the rather high noise level expected. In the laboratory two of the alternative PD detection methods (namely the acoustic method and electrical method including a field probe inside the GIS) have shown a sensitivity to fixed-type defect discharges, while showing less efficiency relative to the mobile particles considered in the study. >

Psychoacoustically Optimal Noise Shaping

Abstract: The design of noise shaping filters for requantization in nonoversampling digital audio applications is examined. The object is to minimize the total perceived output noise power. A new perceptual frequency weighting function is introduced which provides closer matching to the ear's measured sensitivity at high frequencies than do existing functions.

Pixel structure with logarithmic response for intelligent and flexible imager architectures

Abstract: Intended for industrial applications, a pixelstructure with a logarithmic response is presented in this paper. An XY-addressable image architecture based on this pixel was implemented in silicon. Measurement data on this sensor are discussed. The logarithmic response will be quantified using a more general signal to noise ratio. A parallel is drawn with concepts of human perception theory.

Discrete simulation of power law noise

Abstract: Power law noise plays an important role in the description of high performance oscillators. Commonly, five types of noise are considered to affect clocks and clock measurements: white phase, flicker phase, white frequency, flicker frequency and random walk frequency. These noise types are distinguished by the slopes of their spectral densities, S,@ =y (on a log-log scale). The noise is inherent both to the oscillators and to the measurement systems and defines the limits of stability of the clocks. Accurate simulation of the noise can be important for testing the measurement system and the characterization software. This paper presents a new algorithm and computer code for simulating power law noises with arbitrary a (it is not restricted to the integer values mentioned above). The general theory of noise simulation is investigated to determine the criteria for evaluating and deriving simulation methods. Past techniques are evaluted and the new method is shown to provide improvements, particularly because it results in non-stationary noise sequences that are also scale- invariant and causal and have the proper autospectral densities and Allan variances.

Signal separation in a symmetric adaptive noise canceler by output decorrelation

Abstract: An algorithm for adaptive noise cancellation and signal separation is presented. It is an extension of the classical Widrow least-mean-square (LMS) noise canceler for the case of signal leakage into the noise reference. The algorithm is derived intuitively from the interpolation of the adaptive noise canceler as a decorrelator between signal estimate and noise in which the noise reference is replaced by a signal-free noise estimate. Thus, a symmetric adaptive decorrelator is obtained for signal separation, as the artificial distinction between signal and noise concepts has disappeared. The algorithm has its limitations as convergence to the desired solution and stability around it can only be guaranteed for a subclass of signal separation problems. These restrictions are rarely violated in real life problems, however, and seem to be fundamental to the signal separation problem rather than algorithm dependent. >

Estimation of the number of signals in the presence of unknown correlated sensor noise

Abstract: A method for estimating the number of transmitted signals in the presence of spatially correlated sensor noise is proposed. The procedure is developed under the assumption that the unknown noise covariance matrix is a band matrix. In practice, it is quite robust with respect to this finite correlation length assumption. In sensor array processing, this amounts to assuming that the noise field is locally correlated spatially. Since spatial stationarity of the noise is not necessary, it also applies, for instance, to white noise with different power along the array. Simulations indicate that the asymptotic analysis holds for quite small sample sizes. >

Signal interception in non-Gaussian noise

Abstract: The interception of weak signals in nonGaussian noise is discussed. The spectral correlation property exhibited by all cyclostationary signals is exploited to synthesize multi-cycle and single-cycle detectors which assure a superior tolerance (as compared to radiometric techniques) to one of the most challenging problems in interception, namely accommodating unknown and changing noise level and interference activity. The proposed detectors perform a maximum likelihood estimate of the noise level and use the estimate to form the detection statistic. To obtain some analytical information about the performance of the multi-cycle and single-cycle detectors, the deflection, which is a useful measure of the output (signal-to-noise ratio), especially appropriate for weak-signal SNR interception, has been evaluated. The receiver operating characteristics, carried out via computer simulation, confirm the superiority of the proposed cycle detector with respect to the traditional radiometer. >

Apparatus for reducing noise in space applicable to vehicle compartment

Abstract: In an apparatus for reducing noises in a space, signals related to noise generating conditions of a plurality of noise sources are detected, a signal component of the detected signals is selected on the basis of determination of which signal component is predominant over the other signal component in the noises in the space, and the selected signal component is filtered through adaptively determined filter coefficients to output drive signals to control sound source, the filter coefficients being updated through a control algorithm so as to reduce a residual noise of a residual noise detector such as microphones. The signal components to be selected include a signal component having a relatively high auto-correlated function characteristic and a signal component having a random characteristic.