Showing papers on "Noise (signal processing) published in 1982"

A Significance Test for Principal Components Applied to a Cyclone Climatology

Abstract: A technique is presented for selection of principal components for which the geophysical signal is greater than the level of noise. The level of noise is simulated by repeated sampling of principal components computed from a spatially and temporally uncorrected random process. By contrasting the application of principal components based upon the covariance matrix and correlation matrix for a given data set of cyclone frequencies, it is shown that the former is more suitable to fitting data and locating the individual variables that represent large variance in the record, while the latter is more suitable for resolving spatial oscillations such as the movement of primary storm tracks.

Instrument fault detection in systems with uncertainties

Abstract: We demonstrate how to detect instrument faults in non-linear time-varying processes that include uncertainties such as modelling error, parameter ambiguity, and input and output noise. The design of state estimation filters with minimum sensitivity to the uncertainties and maximum sensitivity to the instrument faults is described together with existence conditions for such filters. Simulations based on a non-linear chemical reactor with heat exchange and feedback control illustrate the validity of the proposed method.

Fetal Electrocardiogram Enhancement by Time-Sequenced Adaptive Filtering

Abstract: An adaptive method for performing optimal time-varying filtering of nonstationary signals having a recurring statistical character, e.g., recurring pulses in noise, has been proposed. This method, called time-sequenced adaptive filtering, is applied to the enhancement of abdominally derived fetal electrocardiograms against background muscle noise. It is shown that substantial improvement in terms of signal distortion is obtained when time-sequenced filtering, rather than conventional time-invariant filtering, is employed. The method requires two or more abdominal channels containing correlated signal components, but uncorrelated muscle noise components. The location of the fetal pulses in time must be estimated in order to synchronize the filter's time-varying impulse response to the fetal cardiac cycle.

Signal Processing for Semiconductor Detectors

Abstract: This is a tutorial paper designed to provide a balanced perspective on the processing of signals produced by semiconductor detectors. The general problems of pulse shaping to optimize resolution with constraints imposed by noise, counting rate and rise time fluctuations are discussed.

Équations du filtrage non linéaire de la prédiction et du lissage

Abstract: We establish equations of non linear filtering, prediction (extrapolation) and smoothing (interpolation) in the case where the signal is a non degenerate diffusion process, and the observation is a noisy functional of the signal. We consider both the case of observation noise correlated with the signal, and the opposite case where we establish “robust” form of the equations. We study finally the case of unbounded coefficients, and the case where there is a feedback from the observation to the signal.

Image processing method using a block overlap transformation procedure

Abstract: An image processing method is provided for reducing noise in a sampled image, particularly for reducing noise in an image divided into blocks of sampled image elements that are transformed by a linear procedure, such as the Walsh-Hadamard transform, and improved regarding visible noise by non-linear thresholding of the transform coefficients. By operating the process in a hierarchy of stages, each stage employing a block operating on image signals derived from a preceding stage, and by overlapping the blocks processed in each stage, the processed signal from each image element is the linear combination of many transform coefficients from each stage and from each overlapped block within each stage. Such a large number of contributions making up each processed image element assures that the processed image is generated without a characteristic block-like structure due to block transform processing while the wanted components of the image are rendered with minimal image loss or distortion.

An analysis of signal amplification using small detectors in positron emission tomography.

Abstract: Spatial resolution in computed tomography (CT) has been limited because of the excessive increases in statistical noise associated with increasing resolution. Reconstruction filter functions have been designed to produce tomographic images with resolution as close as possible to the intrinsic detector resolution. Since these filter functions apply an increasing weight to increasing spatial frequencies in the measured data, this produces a large amplification of noise at the upper end of the spatial frequency band of the filter function where the signal from the detector has a low amplitude. This mathematical approach to spatial frequency amplification cannot distinguish between signal and noise and thus both are amplified equally. An approach for improving tomographic resolution is the use of very small detectors to selectively amplify the signal but not noise. This signal amplification technique (SAT) can provide improvements in image resolution without increases in the cutoff frequency of the reconstruction algorithm. Alternatively, in cases in which image counts are low, statistical noise can be reduced by lowering the cutoff frequency. A possible system design for a positron CT system with SAT is described.

Non-orthogonal mobile subscriber multiple access system

Abstract: An adaptive interference cancelling system for multibit spread spectrum noise codes wherein a plurality of users in a mobile subscriber access system each operates with a different noise code. Each user receives a composite signal which includes a desired noise coded signal from another user plus any unwanted interference noise coded signals from other like users in relatively close proximity. The RF demodulator or front end section of each user receiver is coupled to a bank of matched filters which selectively detect and identify any interfering codes. These interfering codes are then regenerated devoid of the desired signal to provide a coherent replica of the interference signal. The received composite signal and the coherent replica of one or more interference signals are applied to individual signal subtractor circuits which operate to cancel the interfering noise coded signals leaving the desired signal to be subsequently matched filter detected free of interference from other users.

Nonlinear Restoration of Noisy Images

Abstract: The restoration of images degraded by an additive white noise is performed by nonlinearly filtering a noisy image. The standard Wiener approach to this problem is modified to take into account the edge information of the image. Various filters of increasing complexity are derived. Experimental results are shown and compared to the standard Wiener filter results and other earlier attempts involving nonstationary filters.

Video device synchronization system

Abstract: A TV video signal synchronization signal system enables a video device such as a digital special effects system to operate synchronously in response to an input video signal and still produce an output video signal synchronized to a television studio locking reference signal. The video device and the synchronization signal generating subsystem thereof operate in response to a pixel rate clock of approximately 70 ns and in response to a phase command to generate timing for the horizontal sync pulse, color burst signal and video data of the output video signal. The output color burst signal remains phase locked to the locking reference signal with output gating being responsive to the phase command. A ROM interpolator provides subpixel accuracy for the output horizontal sync pulse while output line buffering and interpolation permits the output video data to be phase matched to the reference master sync signal. The entire video system thus operates synchronously with the input video signal to avoid noise interference problems which result from multiple phase clock signals while generating a composite output video signal that is properly phase synchronized with a studio locking reference signal.

Estimating the parameters of exponentially damped or undamped sinusoidal signals in noise

Abstract: : We address the problem of estimating the parameters of a signal embedded in noise The signal is composed of samples of a sum of M exponentially damped or undamped sinusoidal signals We suggest improvements to the original approach proposed by Prony He observed that the samples s(n) obey an M th order difference equation and that from the roots of the characteristic polynomial of the difference equation, the parameters (sk) can be determined We present three methods to improve this approach when the signal is noise corrupted

Quantifying resolving power of seismic systems

Abstract: A quantitative formulation of vertical resolving power of seismic exploration systems is presented and is offered as a proposed characteristic, or standard, resolving power identified with individual systems. The formulation broadens the classical concept of resolution by taking into account the reflection waveform and the noise, in addition to the classical time variable. The principal feature in the formulation is the stipulation that the intratrace distribution of reflections and of noise be treated as random (Gaussian) distribution, which is regarded as the most general representation for seismic sections as a whole.Through this quantification of vertical resolving power and therefore of intratrace reflection quality, a number of elemental reflection properties that have been described only qualitatively in the past are expressed by simple formulas. The quantification is consistent with the concept that the resolving power of a noise-free zero-phase system with a flat spectral band response is proportional to the bandwidth. The derived basic formula for the proposed characteristic resolving power is a 2 m /E, where a m is the maximum (absolute) amplitude of the signal wavelet of a seismogram interval, E is the energy of the signal wavelet, and noise is neglected. The quantification of the reflection properties, including taking the noise into account, stems from this formula.The classical concept of resolution, which considers only the time variable, such as the dominant period of signal wavelets, is applicable essentially only in cases of two noise-free equal-strength reflections. In contrast, the proposed formulation of resolving power accommodates a wide scope of applications and might be considered basic to seismic systems. I present theoretical material for evaluating the merits of the proposal. Suitable comparisons by seismic modeling would be useful in the overall evaluation.

Optimal Detection of Digitally Modulated Signals

Abstract: In this paper optimal detectors are derived and analyzed for the general class of digitally modulated signals in which the sequence of symbols is unknown a priori and information data are not of interest. The detectors test the signal present condition in background white Gaussian noise versus the null condition of noise alone. Particular attention is focused upon cases in which the SNR per symbol is low compared to unity. The models employed herein are sufficiently general to include most forms of spread-spectrum signals as well as other digital type communication signals.

The Measurement of Muscle Fiber Conduction Velocity Using a Gradient Threshold Zero-Crossing Method

Abstract: The conduction velocity of myoelectric potential along muscle fiber is known to be an index of the degree of muscular fatigue or muscular disease. When detecting the myoelectric potential by means of surface electrodes, the conduction velocity must be extracted from an apparently random wave of a myoelectric signal. In this paper, a method for determining conduction velocity is proposed based upon a zero-crossing time delay measurement with reference to the derivative of a myoelectric signal. The slope value of the input signal provides an effective criterion for rejecting undesired zero crossing caused by noise. This method needs no spectral analysis nor correlation calculation. Compared to another previously reported zero-cossing approach using digital filter preprocessing, it shows a more accurate and rapid estimation of velocity.

Embedding data in speech using scrambling techniques

Abstract: A method of embedding data into speech signals is proposed. The speech signal is scrambled using the data as the scrambling key, while the receiver adopts the role of a code breaker. By judicious choice of scrambling algorithm the receiver can be made to break the code at every attempt. We found that 126 b/s can be transmitted without error over a channel whose additive noise is only 10 dB below the mean square value of the speech signal.

Frequency modulated heterodyne optical fiber Sagnac interferometer

Abstract: This paper describes a new approach to the detection of rotation rate using the optical fiber Sagnac interferometer. An inherently reciprocal heterodyne system gives the advantages in terms of signal-to-noise ratios (SNR's) of heterodyne detection, while independent electronic monitoring of each propagation path through the interferometer significantly enhances signal processing flexibility. The system may thus be used as a probe to evaluate fiber properties in a way compatible with other architectures, and these measurements should lead to advances in performance characteristics. A prototype system has exhibited noise levels in the region of 100°/h, and improvement to the signal processing will soon improve on this figure.

Automatic background noise suppressor

Abstract: A circuit for suppressing background noise of a continuous nature while enhancing speech signals, or signals having the transient temporal qualities of speech, includes a signal multiplier which, in the preferred embodiment, receives the composite audio signal along with a control signal present only when the speech component of the audio signal is present. The control signal may be derived from an AGC circuit having a slow attack, fast decay characteristic to establish a quiescent output level from the AGC amplifier in the absence of speech. An envelope detector is biased to provide a zero output amplitude in response to the quiescent amplifier output level. Speech components appearing in the amplifier output signal are then envelope-detected and filtered to provide the control signal. Alternatively, the control signal can be derived by envelope-detecting the audio signal, filtering the detected signal to remove its d.c. component representing the continuous noise, and then detecting and filtering again. In still another embodiment, the control signal acts upon a constant amplitude instead of the audio input signal in order to provide a speech-responsive tactile vibration for the deaf.

Noise elimination device

Abstract: A noise elimination device employs a concept of the linear prediction method. According to the invention, a linear prediction coefficient of a digitized, continuous input signal (an original signal) is calculated, a linear predicted value is computed from this linear prediction coefficient, difference (a prediction error) between the linear predicted value and the input signal is computed whereas a threshold value is set in accordance with the momentarily changing input signal, the judgement that a noise has occurred is made when the predicted value has exceeded the threshold value and thereupon a substitution signal is produced on the basis of an input signal existing in the vicinity of the time point at which the noise has occurred, and the section in which the noise has occurred is substituted by this substitution signal thereby to eliminate the noise. By virtue of employing the linear prediction method, the necessity for including an error detection code as a part of data has been obviated, the device is made applicable to elimination of a noise contained in an original signal, possibility of making an erroneous judgement has been reduced even with respect to signals having little correlation between themselves by varying the threshold value in accordance with the input signal, and a sufficient noise suppression effect is expected against a burst error or a relatively long noise by producing a substitution signal resembling an input signal on the basis of the input signal containing no noise in the vicinity of the noise section.

Pulse interference cancelling system for spread spectrum signals utilizing active coherent detection

Abstract: A pulse interference cancelling system for spread spectrum signals utilized in a digital noise coded communications system. The system includes a first and second noise coded signal channel located in a noise coded signal receiver which also includes a demultiplexer for providing a pair of received noise coded signals which were initially generated, multiplexed and transmitted to the receiver. First and second coherent detector means are coupled to both signal channels, the first being directly coupled thereto so that no signal delay exists but the second is coupled to the two signal channels by means of respective first and second variable time delay circuits having a delay substantially equal to the bit width of each digital code as well as a vernier delay which is adapted to delay the phase of any received pulse interference in the respective channel so that it is exactly 180° out of phase with the same undelayed pulse interference. Signal summing means are coupled to the outputs of the two coherent detectors which operate to completely cancel the interference pulse signal while leaving the desired noise coded signal at its peak amplitude.

IR Remote control detector/decoder

Abstract: A pulse code modulated (PCM) infrared (IR) remote control detector/decoder with improved noise immunity particularly adapted for use with a television receiver is disclosed. The IR pulses are modulated by means of a high frequency clock signal in translating the transmitted signal to a higher frequency, more noise immune portion of the IR spectrum. After receipt of the transmitted signal by a signal detector, the high frequency modulation is removed from the pulses which are then decoded. Under the control of a microcomputer, the decoder looks for the start data bit and, if received, the subsequent control instructions. When the data transmission has been decoded, the microcomputer activates the appropriate control outputs to the television receiver's tuner system to achieve the desired control function.

Detecting a hidden periodic signal when its period is unknown

Abstract: A simple method is presented for detecting an unknown periodic signal in additive noise. The period is unknown, but the amplitudes of the fundamental and the first M - 1 harmonics are known to be nonzero. One application is the detection of a torpedo by a submarine sonar system from the observed acoustic line spectrum generated by the torpedo's blade motion.

Endoscope with signal transmission system and method of operating same

Abstract: A signal transmission system for use in an endoscope includes a solid state image sensor for picking up an image of a part of the inside of a cavity of a living body to produce a video signal indicative of the image, a frequency modulator for frequency modulating a carrier frequency with the video signal to produce a frequency modulated signal, video circuitry for receiving the modulated signal to visualize the video signal on a video display, and a transmission circuit for transmitting the modulated signal from the modulator to the video circuitry A frequency band of the frequency modulated signal is selected outside a frequency band of a noise source including an electrical instrument, such as an electrical scalpel

Sidewall-matching adaptive control system for welding

Abstract: An adaptive control system for welding which senses the lateral profile of a weld joint while the welding electrode moves laterally across the joint, compares a first portion of the sensed lateral profile to a second portion of the sensed lateral profile, and then adjusts a welding parameter, such as the center of oscillation for tracking, the width of oscillation, and constant fill control, in response to the results of the comparison. One disclosed signal processing technique matches an average of data samples for the left portion of the weld seam to an average of data samples for the right portion. Another disclosed technique involves comparing an integrated signal corresponding to the leftward portion of the sensed lateral profile to an integrated signal corresponding to the rightward portion. Another disclosed technique involves comparing an integrated sensed profile signal to a predetermined reference value which is based upon a reference signal. The reference signal comprises data representative of the prior history of the weld joint. The disclosed embodiments employ programmed microprocessors to provide horizontal cross-seam control and process the arc signal to remove undesirable noise. The system can adapt to changes in direction of the weld seam as well as changes in the width and shape of the profile of the weld seam.

The optimization of signal detectability in digital fluoroscopy

Abstract: An optimization analysis of digital fluoroscopy has been carried out using (signal/noise)2/dose as a figure of merit. Three signal detection tasks have been considered: (i) small iodine-containing blood vessels; (ii) regions of fat; and (iii) microcalcifications. The effects of x-ray beam filtration and kilovoltage on the figure of merit have been parameterized and the associated x-ray tube power loadings have been defined. Results are presented in a fashion that facilitates the choice of parameters (amount of aluminum filtration, kilovoltage, and x-ray tube power loading) such that an acceptable balance can be achieved between signal detection sensitivity, patient dose, and x-ray tube power loading.

Link quality analyzer

Abstract: A link quality analyzer measures the link quality between a calling station and a called station by continuously transmitting a plurality of signal tones. The called station receives the plurality of transmitting tones and sample them. A power spectrum is obtained of the received tones. From the statistics of the power spectrum the parameters of signal-to-noise ratio, multipath delay spread, Doppler frequency spread, frequency offset statistics, frequency-amplitude correlation, average amplitude response versus frequency, signal fading statistics, harmonic and intermodulation distortions, RMS-to-mean signal ratio, noise profile, and various noise statistics are determined. The power spectrum of the plurality of tones is measured through the use of digital sampling techniques and digital fast Fourier transform techniques that are implemented through microprocessor-level technology.

Noise reduction system for television signals

Abstract: In a system for noise reduction in a television signal utilizing a full frame picture store to enable averaging of corresponding signals of successful frames for noise reduction and having also a motion detector, the signal representing motion is passed through a combination of a low-pass filter and a threshold circuit of which, respectively, the cut-off frequency and the threshold value are controllable as a function of the noise amplitude. As a result, at low noise content of the input signal, no disturbing loss of sharpness of moving edges occurs, whereas at higher noise amplitudes, although noise reduction is at the cost of some loss of edge sharpness, the annoying effects of having noise reduction controlled by the noise itself, are avoided.

Noise reduction apparatus for hybrid image sensor

Abstract: A document sensing device is herein disclosed whereby the signal-to-noise ratio inherent in a large-size image sensor is enhanced by a reduction in system noise. A plurality of photodetectors are connected to a plurality of storage MOSFETs. Two signal wires are connected to alternating groups of the MOSFETs. A shift register is provided which sequentially turns on the MOSFETs. The connections of the groups of MOSFETs and the sequential turn-on sequence are both preselected such that at the same time one group of MOSFETs is outputting a composite signal (information plus noise) on one signal wire, the immediately preceding group of MOSFETs is outputting a signal (noise only) on the other signal wire. Upon the combination of the signals in a differential amplifier, the noise signal is thus eliminated from the composite signal.

Electrostatic voltage control circuit

Abstract: An improved control circuit for protecting a high voltage DC electrostatic system from arcing by removing the high voltage from the electrostatic system under incipient arcing conditions. A signal having a voltage proportional to the instantaneous high voltage current in the electrostatic system is established. DC components and unwanted noise and unwanted AC components are removed from the signal to leave only signal components relating to the rate of change of the current in the high voltage system and information indicative of incipient arcing conditions. When the remaining signal exceeds a predetermined reference level, high voltage is removed from the electrostatic system.