Showing papers on "Noise measurement published in 1989"

Modeling of noise parameters of MESFETs and MODFETs and their frequency and temperature dependence

Abstract: A simple noise model of a microwave MESFET (MODFET, HEMT, etc.) is described and verified at room and cryogenic temperatures. Closed-form expressions for the minimum noise temperature, the optimum generator impedance, the noise conductance, and the generator-impedance-minimizing noise measure are given in terms of the frequency, the elements of a FET equivalent circuit, and the equivalent temperatures of intrinsic gate resistance and drain conductance to be determined from noise measurements. These equivalent temperatures are demonstrated in the case of a Fujitsu FHR01FH MODFET to be independent of frequency in the frequency range in which 1/f noise is negligible. Thus, the model allows prediction of noise parameters for a broad frequency range from a single frequency noise parameter measurement. The relationships between this approach and other relevant studies are established. >

Information and entropy in strange attractors

Abstract: A technique for analyzing time-series data from experiments is presented that provides estimates of four basic characteristics of a system: (1) the measure-theoretic entropy; (2) the accuracy of the measurements; (3) the number of measurements necessary to specify a system state; and (4) the best delay time T to use in order to construct phase space portraits by the method of delays. These characteristics are obtained by separating the entropy of measurements into a part due to noise and parts due to deterministic effects. For the technique to work, the noise associated with each measurement must be independent of the noise associated with all other measurements. An algorithm for implementing the analysis is presented with three examples. >

Effects of phase-to-intensity noise conversion by multiple reflections on gigabit-per-second DFB laser transmission systems

Abstract: Large power penalties and bit-error-rate floors have been observed in some Gb/s systems using distributed feedback (DFB) lasers, which could be attributed to interferometric conversion of laser phase noise to intensity noise by multiple reflections at connectors and splices. The authors calculated the power spectral density of the interferometric noise and its impact on system performance as a function of both the magnitude and number of reflections, and they compare the theoretical predictions with experimental results. Their studies indicate that connectors and splices with return losses of more than about 25 dB are required for the reliable operation of Gb/s fiber transmission systems, even if optical isolators are used. >

Speech reception in quiet and in noisy conditions by individuals with noise-induced hearing loss in relation to their audiogram

Abstract: Tone thresholds and speech-reception thresholds were measured in 200 individuals (400 ears) with noise-induced hearing loss. The speech-reception thresholds were measured in a quiet condition and in noise with a speech spectrum at levels of 35, 50, 65, and 80 dBA. The tone audiograms could be described by three principal components: hearing loss in the regions above 3 kHz, from 1 to 3 kHz and below 1 kHz; the speech thresholds could be described by two components: speech reception in quiet and speech reception in noise at 50-80 dBA. Hearing loss above 1 kHz was related to speech reception in noise; hearing loss at and below 1 kHz to speech reception in quiet. The correlation between the speech thresholds in quiet and in noise was only R = 0.45. An adequate predictor of the speech threshold in noise, the primary factor in the hearing handicap, was the pure-tone average at 2 and 4 kHz (PTA2,4, R = 0.72). The minimum value of the prediction error for any tone-audiometric predictor of this speech threshold was 1.2 dB (standard deviation). The prediction could not be improved by taking into account the critical ratio for low-frequency noise nor by its upward spread of masking. The prediction error is due to measurement error and to a factor common to both ears. The latter factor is ascribed to cognitive skill in speech reception. Hearing loss above 10 to 15 dB HL (hearing level) already shows an effect on the speech threshold in noise, a noticeable handicap is found at PTA2,4 = 30 dB HL.

Spectral analysis of quantization noise in a single-loop sigma-delta modulator with DC input

Abstract: An exact discrete-time analysis of the moments and spectra of the quantization noise of a discrete-time single-loop sigma-delta modulator with a DC input is presented. An exact difference equation for the discrete-time nonlinear system is used to evaluate the first- and second-order moments and power spectrum of the binary quantizer noise and the binary quantizer output for a single-loop sigma-delta encoder with a DC input. It is shown that the sample mean and power of the binary quantization noise are consistent with the common uniform distribution assumption, but that the autocorrelation and power spectrum are not consistent with the white noise assumption. The results are used to evaluate the overall sample average mean squared quantization error as a function of the decimation filter used. >

Speech recognition using noise-adaptive prototypes

Abstract: A probabilistic mixture mode is described for a frame (the short term spectrum) of speech to be used in speech recognition. Each component of the mixture is regarded as a prototype for the labeling phase of a hidden Markov model based speech recognition system. Since the ambient noise during recognition can differ from that present in the training data, the model is designed for convenient updating in changing noise. Based on the observation that the energy in a frequency band is at any fixed time dominated either by signal energy or by noise energy, the energy is modeled as the larger of the separate energies of signal and noise in the band. Statistical algorithms are given for training this as a hidden variables model. The hidden variables are the prototype identities and the separate signal and noise components. Speech recognition experiments that successfully utilize this model are described. >

Impulsive noise suppression and background normalization of electrocardiogram signals using morphological operators

Abstract: An approach to impulsive noise suppression and background normalization of digitized electrocardiogram signals using mathematical morphological operators that incorporate the shape information for a signal is presented. A brief introduction to these nonlinear signal processing operators, as well as a detailed description of the algorithm, is presented. Empirical results show that the algorithm has good performance in impulsive noise suppression and background normalization. >

Responsivity Nonuniformity Limited Performance Of Infrared Staring Cameras

Abstract: . The effect of noise, including system noise, background noise, and cell-to-cell nonuniformity (spatial noise), is mathematically treated and experimentally verified for staring-mode infrared cameras. Spatial noise is shown to be dominant in high background environments (3 to 5 Am or 8 to 12 Am imagery at background temperatures greater than 0°C) even after compensation. Camera sensitivity is quantified by a contrast signal-to-noise ratio that includes the effects of system, background, and spatial noise. Past analysis of camera performance has assumed that the cell-to-cell nonuniformity can be completely removed by using nonuniformity correction techniques. We present data showing that neither variations in detector spectral response nor excess low frequency noise can be fully corrected using existing nonuniformity correction techniques. Furthermore, we show that even the small amounts of nonuniformity that persist after the application of correction algorithms will significantly degrade camera performance.

Accuracy improvements in microwave noise parameter measurements

Abstract: Factors contributing to the accuracy of microwave noise parameter measurements are examined theoretically and experimentally. It is shown that for good accuracy the test source impedances need not be grouped around the impedance that produces the minimum noise figure. System calibration and device under test (DUT) S-parameter accuracy are important to the derived noise parameter accuracy, and the use of a vector network analyzer is advantageous. An algorithm is implemented which avoids errors caused by different noise-source 'on' and 'off' impedances. >

Parametric methods for spatial signal processing in the presence of unknown colored noise fields

Abstract: Two methods for estimation of noise correlations along an array of sensors are presented. Both rely on a parametric (autoregressive moving average) noise model. The model has the advantage of describing the noise correlations by a small number of parameters and can be applied to a great variety of physical noises. The first method is related to the calculation of the likelihood of whitened observations, and the second is related to Pisarenko's method (1973) applied to whitened observations. Both methods are obtained by optimization of a criterion and are iterative. The noise estimates can be used for sensor-output whitening and it then provides a means to improve array processing performance. The two methods perform well, both on simulated and real data. However, the first method seems simpler and more robust than the second. >

Noise characterization of femtosecond fiber Raman soliton lasers

Abstract: The broadband amplitude noise and phase noise (timing jitter) measured in femtosecond fiber Raman soliton lasers is discussed. For a single-pass compressor using 300 m of either standard single-mode fiber or polarization preserving fiber, white amplitude noise >or=50 dB above shot noise at 2 mA photocurrent was measured, for frequencies higher than approximately 100 kHz. This is approximately=30 dB larger than the amplitude noise observed from fiber grating pulse compressors. The timing jitter increases with pump power, and at 1.6 W pump power, 5.2 ps r.m.s. timing jitter was measured, given approximately=2 ps jitter from the Nd:YAG pump. Longer fibers in the single-pass compressor do not affect the amplitude noise, but increase the timing jitter even further. A synchronously pumped ring cavity reduced the timing jitter substantially, but did not significantly improve the amplitude noise. >

On distributed detection with correlated sensors: two examples

Abstract: The authors study the effect of correlated noise on the performance of a distributed detection system. They consider a suboptimal scheme by assuming that the local sensors have the same operating point, and that the distribution of the sensor observation is symmetric. This implies that the joint distribution of the sensor decisions, and therefore the fusion rule, are symmetric functions of the sensor decisions. The detection of a known signal in additive Gaussian noise and in Laplacian noise are considered. In both cases, system performance deteriorates when the correlation between the sensor noises is positive and increasing, whereas the performance improves considerably when the correlation is negative and increasing in magnitude. >

Bispectrum of ship‐radiated noise

Abstract: The bispectrum of ship‐radiated noise is estimated. The noise was received on a towed array being towed by the same ship that served as the noise source. The array was beamformed such that the forward endfire beam pointed toward the towing platform and the broadside beam sampled the environment without the radiated noise of the ship. The results show that there exist frequency‐dependent bispectral components in the ship’s radiated noise, whereas the ambient noise does not contain any significant bispectral components. Since the existence of a nonzero frequency‐dependent bispectrum indicates the existence of nonlinear components in the noise‐generating mechanism, it is concluded that the radiated noise of the towing platform contains such nonlinear mechanisms. Therefore, the bispectrum could be used to indicate the existence of such noise sources as would normally be hidden in the background noise when the usual spectral estimation procedures are applied.

Experimental study of observability of parameter errors in robot calibration

Abstract: The selection of measurement configurations for robot calibration is investigated. The goal is to select a set of robot measurement configurations which will yield maximum observability of the model parameter errors so that the effects of noise in parameter estimation can be minimized. The noise considered includes both measurement and modeling errors. An observability measure is used as a criterion for selecting measurement configurations in calibration. Experimental studies are performed to demonstrate the importance of observability to parameter estimation and to verify its implications in robot calibration. Based on the observability measure defined, the optimal measurement configurations for kinematic model calibration are determined for PUMA-type robots. >

Artificial intelligence pattern-recognition-based noise reduction system for speech processing

Abstract: A system is provided to reduce noise from a signal of speech that is contaminated by noise. The present system employs an artificial intelligence that is capable of deciding upon the adjustment of a filter subsystem by distinguishing between noise and speech in the spectrum of the incoming signal of speech plus noise. The system does this by testing the pattern of a power or envelope function of the frequency spectrum of the incoming signal. The system determines that the fast changing portions of that envelope denote speech whereas the residual is determined to be the frequency distribution of the noise power. This determination is done while examining either the whole spectrum, or frequency bands thereof, regardless of where the maximum of the spectrum lies. In another embodiment of the invention, a feedback loop is incorporated which provides incremental adjustments to the filter by employing a gradient search procedure to attempt to increase certain speech-like features in the system's output. The present system does not require consideration of minima of functions of the incoming signal or pauses in speech. Instead, the present system employs an artificial intelligence system to which is input the envelope pattern of the incoming signal of speech and noise. The present system then filters out of this envelope signal the rapidly changing variations of the envelope over fixed time windows.

A novel differential mode rejection network for conducted emissions diagnostics

Abstract: A differential mode rejection network (DMRN), a device which separates common mode noise from differential mode noise in a line impedance stabilization network (LISN)-based conducted emissions setup, is described. Although it is not a filter, its function is analogous to that of a filter. The DMRN filters out differential mode, and passes common mode unfiltered. The differential mode is attenuated by more than 50 dB, and the common mode noise is attenuated by less than 4 dB. Applications of the DMRN are discussed for filter design and troubleshooting, and electromagnetic interference source suppression is briefly described. Mathematical analysis and hardware implementation of the devices are explained. >

Fiber optic link noise measurement and optimization system

Abstract: Apparatus for optimizing system performance for use in a transmission and signal distribution system which includes at least one fiber optic link having transmission and receiving means The apparatus includes apparatus for measuring noise signals in each fiber optic link and apparatus for generating system performance data corresponding to the noise signals measured by the noise measurement apparatus

Distributed detection of a signal in generalized Gaussian noise

Abstract: The problem of distributed detection of a signal in incompletely specified noise is conducted. The noise assumed belongs to the generalized Gaussian family, and the sensors in the distributed network use the Wilcoxon test. The sensors pass the test statistics to a fusion center, where a hypothesis testing results in a decision regarding the presence or the absence of a signal. Three monotone and admissible fusion center tests are formulated. Restricted numerical evaluation over a certain parameter range of the noise distribution and the range of signal-level indicates that these tests yield performances at comparable levels. >

Extended variances and autoregressive/moving average algorithm for the measurement and synthesis of oscillator phase noise

Abstract: Two related aspects are discussed of the recent research work carried out at Portsmouth Polytechnic in the UK regarding numerical and digital techniques for the measurement and synthesis of phase noise in oscillators. The first aspect concerns the introduction of a statistical quantity termed extended Hadamard variance to be applied in frequency stability analysis by making use of digital frequency counter measurements. The properties, the potential interest and the usefulness of this parameter are briefly demonstrated and applied to the study of a signal from a synthesizer that is frequency-modulated by white noise followed by the frequency counter and signal processing. It is shown that not only the Hadamard variance but also the Allan variance and the extended two-sample variance are sets of this variance. The second aspect refers to modern requirements for numerical simulation of random noise, emulating phase or frequency fluctuations. The authors describe the autoregressive integrated moving average technique used to generate various types of random noise, including radio propagation FM noise, and the Monte Carlo approach to transform from one distribution to another. >

A Novel Approach to the Simultaneous Measurement of Phase and Amplitude Noises in Oscillator

Abstract: This paper presents a signal processing technique called time-domain phase unwrapping applied to the measurement of phase noise in oscillators and which overcomes the dynamic range problem of using phase detectors The technique can be applied also to the measurement of the amplitude noise of the oscillator In this paper, the associated theories and the preliminary experimental results are included

The effects of noise on frequency-domain parameter estimation of synchronous machine models

Abstract: The authors present results of a study conducted to evaluate the effects of measurement noise on the estimation of machine parameters from standstill frequency response test data. Results obtained indicate that, because the test data are inherently noise-corrupted, multiple solution sets can be obtained. Moreover, some of the estimated machine parameters could be unrealistic. It is shown that the results are very sensitive to the value of armature resistance used in the data analysis. Even a 0.5% error in the value of armature resistance could result in unrealistic estimation of the machine parameters. >

Exact noise analysis of SC circuits and an approximate computer implementation

Abstract: A noise analysis of switched-capacitor (SC) circuits is presented that describes the time-averaged second-order statistics of the cyclostationary processes encountered in such systems. A unified framework makes it possible to take into account broadband, as well as low-frequency (such as flicker), noise sources by basing the modeling for all noise types on the mathematical white-noise model in which broadband noise is modeled by white noise and low-frequency noise by linearly filtered white noise. The noise signal decomposition used is different from that used in previous approaches and leads to simple and straightforward computer implementations on various approximation levels. On the basis of this solution, existing SC circuit analyzers featuring different abstraction levels can easily be extended with the noise analysis feature by using much of their original routines. As an example, an implementation of the noise analysis for the WATSCAD program is described. >

Phase Noise Analysis in Radar Systems Using Personal Computers

Abstract: Part 1 Basic tools used in phase noise analysis: phase noise and oscillator theory the effects of time delays of phase noise: phase lock loop design the noise-reduction effects of signal processing with an FFT the measurement of phase noise. Part 2 Phase noise effects on radar subsystems and systems: the radar range calculations and noise effects computing system noise floor by integrating phase noise - a source's phase noise leakage through a mixer receiver gain design with the effects of phase noise leakage phase noise effects on quadrature detection oscillator phase noise specification to determine a system's noise floor phase noise analysis on example radar systems.

The noise bandwidth of sampled data systems

Abstract: The effect of aliasing on sampled noise power measurements is investigated. It is shown that although aliasing does not bias noise power measurements, it can significantly increase the measurement variance. The equivalent noise bandwidth (EENBW) of a sampled data system is defined by equating the mean and variance of the noise power measurement to those of a system with a rectangular spectral response. With this definition, which is shown to be consistent with that for analog systems, it follows that the ENBW is bounded by the smaller of the analog ENBW or half the sampling frequency. Practical examples of sampled-data systems are used to demonstrate the increased variance, integration time, and noise spectral density that accompany aliasing. >

A CAD-oriented method for noise figure computation of two-ports with any internal topology

Abstract: A method for computer-aided noise analysis and an algorithm for the noise-parameter computation of two-ports with any internal topology are discussed. The set of noise parameters that can be calculated by the method includes the noise figure, the correlation matrix of the outgoing noise waves at the input and output ports, the minimum noise figure, the optimum signal reflection coefficient, and the parameter N. The approach is applicable to circuits composed of any number of passive linear multiports and active liner two-port devices. The noise analysis is based on the scattering-matrix description for circuit elements and wave representation for noise. At microwave frequencies, a treatment of noise in terms of waves is more attractive. >

The effects of subtractive-type speech enhancement/noise reduction algorithms on parameter estimation for improved recognition and coding in high noise environments

Abstract: The authors present the results of a study designed to investigate the effects of subtractive-type noise reduction algorithms on LPC-based spectral parameter estimation as related to the performance of speech processors operating with input SNRs of 15 dB and below. Subtractive noise preprocessing greatly improves the SNR, but system performance improvement is not commensurate. LPC spectral estimation is affected by the character of the residual noise which exhibits greater variance and spectral granularity than the original broadband noise. The study shows that removing less than the full amount of noise and whitening it improves spectral estimation and speech device performance. Techniques and performance results are presented. >

A comparative study of cepstral lifters and distance measures for all pole models of speech in noise

Abstract: After a brief overview of the techniques utilized, the authors evaluate perceptually based linear prediction (PLP) analysis, and then report the results of a comparative study of several front-ends in the case of speech produced in quiet and noisy environments (Lombard effect). Several all-pole models of speech using various lifters and distance measures are compared in various noise conditions. The main conclusions of this research are: (1) when speech is produced in a quiet environment and in speaker-dependent automatic speech recognition (ASR), the cepstral projection measure significantly improves recognition scores for the three all-pole models considered (for clean reference and noisy test templates), with the best results obtained with the LP analysis (for SNR=5 dB); (2) when speech is produced in a quiet environment and in speaker-dependent and cross-speaker ASR, the optimal filter is a function of the SNR of the test and the reference templates; and (3) when speech is produced in noise and in speaker-dependent ASR, the PLPRPS front-end is the best, and a low model order of the analysis is suitable. >

Spectral estimation using a log-distance error criterion applied to speech recognition

Abstract: A novel algorithm is presented for the estimation of a signal in noise. The distortion criterion used is based on the distance between log spectra. In many signal-processing applications, such as speech recognition, log spectra are much closer to the parameters used in a discriminator than power spectra. Therefore, it is believed that this spectral estimation technique should lead to better results than previously developed techniques such as spectral subtraction. The present technique performed better than spectral subtraction in noise immunity experiments on the IBM isolated word speech-recognition system, although at the expense of additional computational requirements. >