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This paper describes a method for generating long sample paths of accurate fractional Gaussian noise (fGn), the increment process of fractional Brownian motion (fBm). The method is based on a Wold decomposition in which fGn is expressed as the output of a finite impulse response filter with discrete white Gaussian noise as input. The form of the ideal filter is derived analytically in the continuous-time case. For the finite-length discrete-time case, an iterative projection algorithm incorporating a Newton-Raphson step is described for computing the coefficients of a length-N filter in a time approximately proportional to N. Fast convolution of discrete white Gaussian noise with the computed filter impulse response yields arbitrarily long sequences which exactly match the correlation structure of fGn over a finite range of lags. For values of the Hurst parameter H smaller than a critical value [H.sub.crit] [approximately equal to] 0.85, and large N, the finite-length antocorrelation sequence of fGn is positive definite and this range of lags can be as large as the filter autocorrelation length. When H > [H.sub.crit], the finite-length autocorrelation sequence of fGn is no longer positive definite and a modification is made to allow a Wold decomposition. The generated sequences then exactly match the autocorrelation structure of fGn over a more restricted range of lags which becomes smaller as H approaches unity. Index Terms--1/f noise, finite impulse response (FIR) filter synthesis, fractional Brownian traffic, fractional Gaussian noise (fGn), noise generators, spectral factorization.

This paper reports a new delay subspace decomposition (DSD) algorithm. Instead of using the canonical zero-delay correlation matrix, the new DSD algorithm introduces a delay into the correlation matrix of the subspace decomposition to suppress noises in the data. The algorithm is applied to functional magnetic resonance imaging (fMRI) to detect the regions of focal activities in the brain. The efficiency is evaluated by comparing with independent component analysis and principal component analysis method of fMRI. Index Terms--Functional magnetic resonance imaging (fMRI), independent component analysis (ICA), noise suppression, principal component analysis (PCA), subspace decomposition.

A low-complexity algorithm for determining the Bell Labs Layered Space-Time (BLAST) ordering that is facilitated by the noise-predictive architecture is proposed. The ordered noise-prediction minimum-mean-squared-error decision-feedback (DF) detector and its BLAST ordering with low complexity are determined.

The study presents an experiment that adds five perturbing magnets on each of two existing magnets of the magnetron, restoring the axial symmetry of the magnetic field, while maintaining the five-fold azimuthal magnetic field symmetry. The results revealed that the noise close to the carrier is reduced by up to 20 dB, while the sidebands are not completely eliminated for medium and high currents.

Psychological and physiological habituation are major goals in the treatment of patients suffering from chronic tinnitus. This study evaluates whether sound stimulation provided by use of low level white noise generators (NG) enhances the effects of cognitive-behavioral treatment (CBT). 124 outpatients with tinnitus of > 6 months received manualized group treatment and were randomly assigned to the NG/no NG conditions. Those with moderate tinnitus-related distress obtained four sessions focusing on education, while severely distressed subjects were treated according to a full 10-session CBT program. Outcome was assessed at post-treatment and at 6- and 18-month follow-up. No additive effects due to the NGs could be demonstrated. All groups improved significantly on measures of tinnitus-related distress, dysfunctional cognitions, general psychopathology, depression, hypochondriasis and psychosocial functioning. Beneficial effects of the NGs were only observed for patients with concurrent tinnitus and hyperacusis. As systematic physical stimulation of the auditory system does not further improve the effects of CBT, the importance and strength of psychological interventions are emphasized. The clinical relevance of recently developed 'retraining' approaches accentuating physical stimulation should be reconsidered. Keywords: Chronic tinnitus; Cognitive-behavioral treatment; Sound stimulation; Noise generators; Hyperacusis

A procedure is proposed for computing shot noise in resonant-tunneling structures with an arbitrary number of quantum wells.

A nonparametric generalization of the locally optimum Bayes (LOB) parametric theory of signal detection in additive non-Gaussian noise with independent sampling is presented. From a locally asymptotically normal (LAN) expansion of the log-likelihood ratio the nonparametric detector structure, in both coherent and incoherent modes, is determined. Moreover, its statistics under both hypotheses are obtained. The nonparametric LAN log-likelihood ratio is then reduced to a least informative (i.e., having minimum variance under the null hypothesis, Ho) local parametric submodel, which is referred to as adaptive. In the adaptive submodel, certain nonlinearities are replaced by their efficient estimates. This is accomplished such that no information is lost when the noise first-order density is no longer parametrically defined. Adaptive nonparametric LOB detectors are thus shown to be asymptotically optimum (AO), canonical in signal waveform, distribution free in noise statistics, and identical in form (in the symmetric cases) to their parametric counterparts. A numerical example is provided when the underlying density is Middleton's Class-A noise, which demonstrates that even with a relatively small sample size (O([10.sup.2])) adaptive LOB nonparametric detectors perform nearly as well as the classical LOB detectors. Index Terms--Adaptive nonparametric detection, asymptotic optimality, coherent and incoherent reception, locally optimum Bayes (LOB), symmetric or asymmetric noise.

The problem is addressed of synthesizing a generalized Gaussian noise with exponent 1/2, using a nonlinear memoryless transformation applied to a uniform noise.

An electronic noise-generator producing high-dimensional narrowband chaotic signals is reported. The generator has the form of a delayed nonlinear feedback circuit. It has potential applications in secure communications. Index Terms--Chaos, communication systems, cryptography.

The effect of anomalously low cross-spectrum voltage noise density in a two-channel noise measurement system (NMS) is examined, experimentally and theoretically. It is shown that the effect occurs when two thermal noise sources with matched intensities operate at the inputs of a two-channel NMS.

This paper investigates the impact of proton irradiation on the 1/f noise in ultra-high-voltage chemical-vapor deposition SiGe heterojunction bipolar transistors. The relative degradation of 1/f noise shows a strong dependence on device geometry. Both the geometry dependence and the bias dependence of 1/f noise change significantly after exposure to 2 x [10.sup.13] p/[cm.sup.2] protons. An expression describing the 1/f noise is derived and used to explain the experimental observations. Index Terms--1/f noise, proton irradiation, SiGe heterojunction bipolar transistor (HBT).

The possibility to generate noise-induced directed quantum currents in periodic structures of minimal complexity namely, the rectification of quantum noise in periodic tight binding lattices is discussed. The combined use of dissipation and nonequilibrium, asymmetric driving forces was used to obtain a finite directed current.

Research is presented concerning the frequency stabilization of microwave oscillators through the configuration of interferometric frequency discriminators. Single direction and dual reflection frequency discriminators are discussed.

A image-smoothing method, a nonlinear filter, based on a model of spatial processing seen in early stages of human vision has been developed. The main problem in preserving edges and smoothing images is in distinguishing between meaningful contours and noise, so that the image can be smoothed without detail loss. The filter is based on the psychophysical phenomenon of human visual contrast sensitivity.

Evoked dipole responses in unknown spatially correlated noise with EEG/MEG arrays have been estimated. Maximum likelihood (ML) ways of estimating evoked dipole responses using magnetoencephalography (MEG) and electroencephalography (EEG) arrays and an ML-based method for scanning brain response data are proposed. They make possible space-correlated noise between sensors with covariance not known. The electric source is modeled as a collection of current dipoles at fixed locations and the head as a spherical conductor. It can be used to state the multidimensional search needed to get the true dipole location estimates. Simulations show performance.

Results indicate that the likely source of the low frequency noise in the GaAs metal-semiconductor field-effect transistors is charge fluctuations in the Shockley-Read-Hall centers in the depleted layer situated below the gate electrode.

Stability analysis of a modeled flowfield offers a way to estimate frequencies associated with flow instability. The flow features of a flap side edge have been derived from a computational, experimental database.

The analog simulation of nonlinear dynamical systems is advantageous in some cases, i.e., when compared with the study using digital computers and, in particular, when one wishes to investigate the role of noise in these systems. In the present work we introduce two different methods of introducing a noise component in the most widely used chaotic circuit, namely, Chua's circuit, and apply these methods to study the effect of noise on identically driven chaotic circuits. Index Terms - Chaos, Chua circuit, noise, nonlinear circuits, stochastic systems.

The conventional signal demodulator of a chopper amplifier can be substituted by track-and-hold (T/H) and averaging functions. This arrangement provides offset cancellation without requiring low-pass filters and can ignore the residual offset generated by input spikes. A noise analysis shows that this T/H demodulator degrades the white noise signal-to-noise ratio (SNR), although degradation can be minimized by using maximum duty cycle and minimum amplifier bandwidth. Index Terms - Broadband white noise semiconductor, chopper amplifiers, offset cancellation, track and hold demodulator.

The problem of estimating the unknown parameters of an autoregressive (AR) signal observed in white noise, including the signal power and the noise variance, is studied. A new type of least-squares method is developed which is based on a simple technique of estimating the observation noise variance by increasing the degree of the underlying AR model by one. The main feature of the presented method is that the consistent estimates of AR parameters can he directly achieved, with no need to prefilter noisy data or to make any parameter transformation. Index Terms - Autoregressive processes, least-squares method, parameter estimation.

This paper investigates the timing jitter of single-ended and differential CMOS ring oscillators due to supply and substrate noise. We calculate the jitter resulting from supply and substrate noise, show that the concept of frequency modulation can be applied, and derive relationships that express different types of jitter in terms of the sensitivity of the oscillation frequency to the supply or substrate voltage. Using examples based on measured results, we show that thermal jitter is typically negligible compared to supply- and substrate-induced jitter in high-speed digital systems. We also discuss the dependence of the jitter of differential CMOS ring oscillators on transistor gate width, power consumption, and the number of stages. Index Terms - Jitter, oscillator, phase-locked loops, supply noise.

Research was conducted to examine a proposed structure for the separation and tracking of uncorrelated sources by means of a 2-dimensional adaptive array with no a priori knowledge on source locations. The estimated locations of the sources were used to measure the preprocessing weights of the beamformer while the beamformer outputs were used for the continuous calculation of the source locations. Results suggest that although the proposed structure may have erratic initial convergence behavior, it tracks fast, is simple to operate and well suited for mobile communications systems.

The voltage fluctuations in magnetic tunnel junctions exhibiting both high and low magnetoresistance were measured as a function of temperature, magnetic field and voltage bias. Junctions with nearly equivalent magnetic electrodes but having significantly different magnetoresistance were compared. Experimental results showed that junctions with low magnetoresistance possess significantly higher noise power whose origin is not magnetic. Random telegraph noise in these junctions was observed over a wide range of temperatures and junction biases.

A one-dimensional bipolar Monte Carlo simulator was used to examine under forward-bias conditions of the physical origin of high frequency noise phenomena characterizing the properties of Si1-xGex/Si heterojunctions. Current fluctuations in homojunction and heterojunction in comparison with p+n homojunction were investigated through a comparative microscopic analysis. The findings are discussed.

First order and low-frequency noise generated by GaInP/GaAs heterojunction bipolar transistors were measured. Passivated transistors had higher gain values. Noise was measured in the 1 Hz to 100 kHz frequency range on common-emitter-mounted transistors. The 1/f component was examined and the emitter series resistances were obtained. The nearness of the base contact on the smaller devices resulted in a higher noise level because of increased recombinations.

The excess noise factor in thin p(super +)-i-n(super +) GaAs avalanche photodiodes has been computed by using the Monte Carlo method. A numerical model has been derived which takes into account the dependence of the noise factor on multiplication length in these devices. The probability distribution of multiplication for electrons and holes in devices with different multiplication lengths but equal mean multiplication has also been determined. The shapes of the distribution are then compared with ionization path length which has also been obtained from the model.

The noise-equivalent temperature difference is a measure of the detector-noise-limited sensitivity of single-band IR systems for noncontact temperature measurement. However, because its definition is based on the signal-to-noise ratio in a single detector channel, the notion of noise-equivalent temperature difference must be generalized in case of dual-band or multiband IR systems. A new measure of temperature-measurement sensitivity is proposed that can be used to describe single-band, dual-band, and multiband IR measurement systems. With this measure a comparison of temperature-measurement accuracy among single-band, dual-band, and multiband systems was carried out.

The gain and noise characteristics of avalanche photodiode (APD) arrays of the bevel-edge type were calculated. Results showed that the noise of the APD array is dominated by the interpixel resistance at low voltages. In calculating the frequency response of the APD arrays and comparing it with PIN diodes, it is shown that APD's have better performance than at high frequencies.

Low frequency noise properties of new high voltage, high performance complementary polysilicon emitter bipolar transistors were investigated. The effect of the base biasing resistance, emitter geometry and temperature on the noise spectra was examined. The npn transistors showed 1/f and shot noise. In contrast, the pnp transistors had substantial generation-recombination noise contributions to the total noise.

Research was conducted to study the error probability of a digital circuit node exposed to thermal noise agitation and to examine the minimal dissipation-reliability relation for electronic circuits. Circuit values were set a lower bound to the power consumption of the total system. Results showed that the maximal error probability each node permitted by the reliability requirement of the total system resulted to a minimal node energy dissipated per logical switching.

Research was conducted to characterize a theoretical model for the noise properties of Schottky barrier diodes in the context of the thermionic-emission-diffusion theory. Electron transport through the semiconductor was described by the drift-diffusion model while the boundary conditions mirrored the behavior of the quasi-Fermi level related to the metal-semiconductor contact. Results showed that the model is capable of closed analytical expressions to analyze terms related to the impedance, voltage and current fluctuations.

Research was conducted to describe a procedure that performs local noise distribution analysis of a semiconductor junction when both the drift and diffusive parts of the current are critical. The method is characterized by space-inhomogeneous and hot-carrier conditions in the framework of a drift-diffusion model. Results indicated that the method can be applied into any device model based on the drift-diffusion approach and its modifications.

We derive a series of upper and lower bounds for the minimum distance between two noise-free output sequences over unknown channels with fixed-energy finite-duration impulse responses. Using these bounds, we develop a method for determining the minimum distance. Such distance is crucial for determining the worst possible performance of maximum-likelihood sequence estimation (MLSE). Index Terms - Maximum-likelihood sequence estimation, minimum distance, unknown channel.

Mathematical analysis is used to select the optimum drain current for low thermal noise operation in short-channel submicrometer complementary metal-oxide-semiconductor transistors (CMOS). Two noise sources from discrete regions in the transistor's channel appear to be dependent on drain current. Equations to calculate the optimum drain current are illustrated. The graphical relationship of drain current verses spectral density of the Equivalent Thermal Noise Voltage are shown.

Research using the steady-state Nyquist theorem for multiterminal devices has established a high-frequency analytical noise model capable of catering for shot noise induced by the gate leakage current. The model specifies the minimum noise figure of submicrometer gate-length high-electron-mobility transistors and expresses optimum source impedance in laboratory studies. It can be used in the design of microwave low noise amplifiers.

A study was conducted on the effects of electrical stress on static characteristics and power spectral density, Slb+, of base current, Ib+, fluctuations at low frequencies, f

The SARF technique was used to characterize a set of Al-1% submicrometric metal lines. The lines exhibited a bamboo structure in which the grain boundary electromigration is inhibited. Three different phenomena were identified capable of generating resistance microfluctuations. A measured activation energy of 1.4 eV confirmed that bulk electromigration sas the main cause of noise generation

The major advantages of the bipolar junction transistors (BJT's) are associated with its high speed functions and low noise characteristics. Research is conducted to study the noise characteristics of polysilicon bipolar transistor. Effects of varied chemical treatments and annealing temperatures on the noise magnitude of the BJT's, before and after polysilicon deposition are discussed.

An undergraduate experiment is described in which the output of a noise generator is sampled by a computer equipped with a data acquisition board, after which the autocorrelation function is calculated. If the output of the noise generator passes through a low-pass filter before it is sampled by the computer, then the autocorrelation function is a decreasing exponential function with a decay constant equal to the time constant of the low-pass filter. The theory necessary to understand this phenomenon involves basic concepts in electrical noise, the analysis of linear systems, and Fourier transforms. In this paper the theoretical background for the experiment is discussed, typical data are presented, and a full analysis of these data is described.

Phase noise in solid state oscillators arises in part from residual phase noise in the active device that provides gain. The device's residual phase noise is usually attributed to baseband noise on the bias that upconverts via a mixing process to generate phase noise around the carrier signal. This conclusion is consistent with the observation that baseband and carrier noise sources both have 1/f spectral properties. However, similar spectral properties are not sufficient to prove that the baseband and carrier noise are fully correlated. Experimental results presented here for a heterojunction FET show less than 40% correlation. To account for these observations a new 1/f noise model is presented. This model is used to accurately predict the phase noise when a bias feedback circuit is added to stabilize the baseband fluctuations.

A simple but accurate expression for general non-stationary noise correlation i the presence of a recorded transition is analyzed in terms of both noise voltag and spectral measurements. The parameters of this analysis are solely the cross track correlation width s, the transition shape and parameter a, the head-mediu spacing d, and the replay gap length g. It is shown that although the noise varies continuously through the transition, a reasonable decomposition that accounts for a large percentage of the total noise is into conventional positio and amplitude jitter of a fixed transition shape. The relative weights depend o the head-medium parameters; for current head-medium configurations and for longitudinal recording, position jitter dominates. A simple closed form expression for the noise power spectrum is given. Published experimental measurements of signal and noise spectra made with pseudo-random write data compare extremely well with this theoretical analysis, and lead to very good estimates for a and s. The analysis is general and applies for low-density recording with both inductive and magnetoresistive heads as well as all magnetization orientations.