Showing papers on "Noise (signal processing) published in 2002"

Stochastic resonance in biology. How noise can enhance detection of weak signals and help improve biological information processing.

Abstract: Noise is usually thought of as the enemy of order rather than as a constructive influence. In nonlinear systems that possess some sort of threshold, random noise plays a beneficial role in enhancing the detection of weak information-carrying signals. This phenomenon, termed stochastic resonance, does find useful applications in physical, biological, and biomedical contexts. Certain biological systems may even use this effect for optimizing function and behavior.

Method and arrangement for communicating between vehicles

Abstract: Method for transferring information between a vehicle and a transmitter in which a unique pseudorandom noise signal is transmitted by the transmitter in a carrier-less fashion composed of frequencies within a pre-selected band. Information is encoded in the noise signal relating to an identification of the transmitter and a position of the transmitter and the vehicle is provided with a device for extracting the information from the noise signal. The code to use for encoding the noise signal may be selected based on the position of the transmitter so that analysis of the code, or a portion thereof, provides an indication of the position of the transmitter. Information about accidents, weather conditions, road conditions, map data and traffic control devices and about errors in a GPS signal can also be encoded in the noise signals. The transmitter may be at a fixed location or in another vehicle to thereby enable vehicle-to-vehicle communications for the purposes of collision avoidance, intelligent highway applications and the like.

Methods and apparatus for monitoring consciousness

Abstract: The application discloses several inventions as follows: (a) a method of monitoring consciousness of a sentient subject and automatically detecting transition states by obtaining an EEG signal and comparing the two signals to detect the transition and provide a warning signal when the transition occurs; (b) a method or apparatus for processing a non-stationary signal including segments having increasing and decreasing amplitude representing physiological characteristics of a sentient subject by performing syntactic analysis of segments, comparing height, width and error parameters of segments to identify noise segments and replacing noise segments with a straight line before classifying the signal as belonging to one of predefined sleep states; (c) a method of monitoring physiological characteristics of a sentient subject including substitution of a degraded first electrode signal by a second spare electrode signal and providing a warning signal when both signals are degraded; and (d) a capacitive or inductive element sensor for detecting the degree of opening of the eyelid including signal providing means indicative of the relative positions between a component movable with the eyelid and a reference component.

Deconvolution in astronomy: A review

Abstract: This article reviews different deconvolution methods. The all-pervasive presence of noise is what makes deconvolution particularly difficult. The diversity of resulting algorithms reflects different ways of estimating the true signal under various idealizations of its properties. Different ways of approaching signal recovery are based on different instrumental noise models, whether the astronomical objects are pointlike or extended, and indeed on the computational resources available to the analyst. We present a number of recent results in this survey of signal restoration, including in the areas of superresolution and dithering. In particular, we show that most recent published work has consisted of incorporating some form of multiresolution in the deconvolution process.

GSVD-based optimal filtering for single and multimicrophone speech enhancement

Abstract: A generalized singular value decomposition (GSVD) based algorithm is proposed for enhancing multimicrophone speech signals degraded by additive colored noise. This GSVD-based multimicrophone algorithm can be considered to be an extension of the single-microphone signal subspace algorithms for enhancing noisy speech signals and amounts to a specific optimal filtering problem when the desired response signal cannot be observed. The optimal filter can be written as a function of the generalized singular vectors and singular values of a speech and noise data matrix. A number of symmetry properties are derived for the single-microphone and multimicrophone optimal filter, which are valid for the white noise case as well as for the colored noise case. In addition, the averaging step of some single-microphone signal subspace algorithms is examined, leading to the conclusion that this averaging operation is unnecessary and even suboptimal. For simple situations, where we consider localized sources and no multipath propagation, the GSVD-based optimal filtering technique exhibits the spatial directivity pattern of a beamformer. When comparing the noise reduction performance for realistic situations, simulations show that the GSVD-based optimal filtering technique has a better performance than standard fixed and adaptive beamforming techniques for all reverberation times and that it is more robust to deviations from the nominal situation, as, e.g., encountered in uncalibrated microphone arrays.

Method and apparatus for estimating physiological parameters using model-based adaptive filtering

Abstract: A method and apparatus for reducing the effects of noise on a system for measuring physiological parameters, such as, for example, a pulse oximeter. The method and apparatus of the invention take into account the physical limitations on various physiological parameters being monitored when weighting and averaging a series of measurements. Varying weights are assigned different measurements, measurements are rejected, and the averaging period is adjusted according to the reliability of the measurements. Similarly, calculated values derived from analyzing the measurements are also assigned varying weights and averaged over adjustable periods. More specifically, a general class of filters such as, for example, Kalman filters, is employed in processing the measurements and calculated values. The filters use mathematical models which describe how the physiological parameters change in time, and how these parameters relate to measurement in a noisy environment. The filters adaptively modify a set of averaging weights to optimally estimate the physiological parameters.

Statistical properties of logarithmically transformed speckle

Abstract: In synthetic aperture radar (SAR) image processing and analysis, the logarithmic transform is often employed to convert the multiplicative speckle model to an additive noise model. However, this nonlinear operation totally changes the statistics of SAR images. In this communication, we first review the statistical properties of speckle noise in both the intensity and the amplitude formats. Then, we derive the probability density functions, the mean values, and the variances to characterize the log-transformed speckle. Finally we discuss the problems introduced by the logarithmic transform on statistical analysis of SAR images. The statistical models developed in this communication will facilitate subsequent SAR image processing tasks based on the additive noise model.

Noise suppression for speech signal in an automobile

Abstract: Techniques for suppressing noise from a signal comprised of speech plus noise. A first signal detector (e.g., a microphone) provides a first signal comprised of a desired component plus an undesired component. A second signal detector (e.g., a sensor) provides a second signal comprised mostly of an undesired component. The adaptive canceller removes a portion of the undesired component in the first signal that is correlated with the undesired component in the second signal and provides an intermediate signal. The voice activity detector provides a control signal indicative of non-active time periods whereby the desired component is detected to be absent from the intermediate signal. The noise suppression unit suppresses the undesired component in the intermediate signal based on a spectrum modification technique and provides an output signal having a substantial portion of the desired component and with a large portion of the undesired component removed.

Optimal speech enhancement under signal presence uncertainty using log-spectral amplitude estimator

Abstract: We present an optimally modified log-spectral amplitude estimator, which minimizes the mean-square error of the log-spectra for speech signals under signal presence uncertainty. We propose an estimator for the a priori signal-to-noise ratio (SNR), and introduce an efficient estimator for the a priori speech absence probability. Speech presence probability is estimated for each frequency bin and each frame by a soft-decision approach, which exploits the strong correlation of speech presence in neighboring frequency bins of consecutive frames. Objective and subjective evaluation confirm superiority in noise suppression and quality of the enhanced speech.

Wavelet-based analysis of pulse oximetry signals

Abstract: A pulse oximetry signal, suitably a photoplethysmogram (PPG), is decomposed by wavelet transform techniques, and the decomposed signal analysed to provide selected physiological data. The signal may be processed to remove noise, artefacts, or transient features. Information on respiration may also be recovered.

A nonlinear adaptive method of elimination of power line interference in ECG signals

Abstract: A new method of elimination of power line noise in electrocardiogram signals is presented. The proposed method employs, as its main building block, a recently developed signal processing algorithm capable of extracting a specified component of a signal and tracking its variations over time. Design considerations and performance of the proposed method are presented with the aid of computer simulations. Superior performance is observed in terms of effective elimination of noise under conditions of varying powerline interference frequency. The proposed method presents a simple and robust structure which complies with practical constraints involved in the problem such as low computational resource availability and low sampling frequency.

A Novel Broadband Ultrasonic Location System

Abstract: Indoor ultrasonic location systems provide fine-grained position data to ubiquitous computing applications. However, the ultrasonic location systems previously developed utilize narrowband transducers, and thus perform poorly in the presence of noise and are constrained by the fact that signal collisions must be avoided. In this paper, we present a novel ultrasonic location system which utilizes broadband transducers. We describe the transmitter and receiver hardware, and characterize the ultrasonic channel bandwidth. The system has been deployed as a polled, centralized location system in an office. Test results demonstrate that the system can function in high levels of environmental noise, and that it has the capability for higher update rates than previous ultrasonic location systems.

Noise suppression for a wireless communication device

Abstract: Techniques to suppress noise from a signal comprised of speech plus noise. In accordance with aspects of the invention, two or more signal detectors (e.g., microphones) are used to detect respective signals having speech and noise components, with the magnitude of each component being dependent on various factors such as the distance between the speech source and the microphone. Signal processing is then used to process the detected signals to generate the desired output signal having predominantly speech with a large portion of the noise removed. The techniques described herein may be advantageously used for both near-field and far-field applications, and may be implemented in various mobile communication devices such as cellular phones.

Blind noise reduction for multisensory signals using ICA and subspace filtering, with application to EEG analysis.

Abstract: In many applications of signal processing, especially in communications and biomedicine, preprocessing is necessary to remove noise from data recorded by multiple sensors. Typically, each sensor or electrode measures the noisy mixture of original source signals. In this paper a noise reduction technique using independent component analysis (ICA) and subspace filtering is presented. In this approach we apply subspace filtering not to the observed raw data but to a demixed version of these data obtained by ICA. Finite impulse response filters are employed whose vectors are parameters estimated based on signal subspace extraction. ICA allows us to filter independent components. After the noise is removed we reconstruct the enhanced independent components to obtain clean original signals; i.e., we project the data to sensor level. Simulations as well as real application results for EEG-signal noise elimination are included to show the validity and effectiveness of the proposed approach.

Image processing apparatus and method

Abstract: An image processing apparatus and method which can reduce the size of circuits for alpha-blending and dithering and realize high speed processing which perform in parallel processing for finding an amount of update of present image data to be drawn with respect to image data already stored in a display buffer by using a blending coefficient in a subtractor and a multiplier and processing for adding noise data to the image data already stored in the display buffer in a first adder and adding the data obtained by the two processing at a second adder so as to find data comprised of noise data added to data obtained by linear interpolation of two colors, then extracting color valid values at a clamp circuit, thinning out the extracted data in a rounding-off circuit, and writing it back to the display buffer.

Adaptive noise cancelling microphone system

Abstract: An adaptive noise canceling microphone system for extracting a desired signal, in particular a desired speech signal, comprising two microphones being arranged at a predefined distance from each other; a signal forming system (SFS) being adapted to receive a first and second input signals resulting from sounds received by the two microphones wherein an acoustical signal component in the first input signal is determined, wherein an acoustical signal component in the second input signal is determined, wherein the acoustical signal component in the first input signal is enhanced to generate a speech enhanced signal, and wherein the acoustical signal component in the second input signal is suppressed to generate a speech nulled signal; an adaptive noise cancellation filtering circuit being adapted to receive the speech enhanced signal and the speech nulled signal, wherein the noise in the speech enhanced signal is cancelled using the speech nulled signal as reference, thereby generating an output filtered signal representing the desired signal.

Radio frequency characterization of cable plant and corresponding calibration of communication equipment communicating via the cable plant

Abstract: A switch router and one or more gateways incorporating a diagnostic and calibration system that performs RF characterization of an underlying cable plant The switch router is connected at a point of insertion or point of distribution and each gateway is located downstream, such as at corresponding subscriber locations The switch router and each gateway sends a test signal with known characteristics and power level, and the receiving device determines noise level and power loss for the corresponding downstream and upstream channel pair The power loss information is used to calibrate the power level of the transmitters The noise levels are used to determine if the selected modulation schemes employed for normal communications is realizable A frequency analysis, such as FFT or the like, is performed on the upstream test signal spectrum to derive valuable frequency information for the upstream channel or the entire upstream bandwidth

Ordered successive interference cancellation receiver processing for multipath channels

Abstract: Techniques to process a number of “received” symbol streams in a Multiple-Input Multiple-Output (MIMO) system with multipath channels such that improved performance may be achieved when using successive interference cancellation (SIC) processing. In an aspect, metrics indicative of the quality or “goodness” of a “detected” symbol stream are provided. These metrics consider the frequency selective response of the multipath channels used to transmit the symbol stream. For example, the metrics may relate to (1) an overall channel capacity for all transmission channels used for the symbol stream, or (2) an equivalent signal-to-interference noise ratio (SNR) of an Additive White Gaussian Noise (AWGN) channel modeling these transmission channels. In another aspect, techniques are provided to process the received symbol streams, using SIC processing, to recover a number of transmitted symbol streams. The particular order in which the symbol streams are recovered is determined based on the metrics determined for symbol streams detected at each SIC processing stage.

Bandwidth-efficient wireless network modem

Abstract: Wireless communication network dynamically assigning communicators to allocated channels by considering the interference and noise environment to maximize the number of communicators and effective bandwidth of the channel. The present invention provides a digital wireless modem capable of measuring interference and noise in a channel, signaling the information on a control channel, accepting dynamic channel assignments from a controlling element and demodulating signals in the presence of interference and noise. The modem uses a demodulator (92 and 94) capable of recovering information from data signals in the presence of noise and interference stronger than the primary signal, and there is a controlling element (102) for transmitting noise and interference measurements to a central network controller and a controlling element (105) for determining channel assignments with the central network controller and setting the modem to the correct transmission and reception channel.

Digital, phase-sensitive detection for in situ diode-laser spectroscopy under rapidly changing transmission conditions

Abstract: A new harmonic detection scheme for fully digital, fast-scanning wavelength-modulation spectroscopy (DFS-WMS) is presented. DFS-WMS is specially suited for in situ absorption measurements in combustion environments under fast fluctuating transmission conditions and is demonstrated for the first time by open-path monitoring of ambient oxygen using a distributed-feedback diode laser, which is doubly modulated with a fast linear 1 kHz-scan and a sinusoidal 300 kHz-modulation. After an analog high-pass filter, the detector signal is digitized with a 5 megasample/s 12-bit AD-converter card plugged into a PC and subsequently – unlike standard lock-ins – filtered further by co-adding 100 scans, to generate a narrowband comb filter. All further filtering and the demodulation are performed completely digitally on a PC with the help of discrete Fourier transforms (DFT). Both 1f- and 2f-signals, are simultaneously extracted from the detector signal using one ADC input channel. For the 2f-signal, a linearity of 2% and a minimum detectable absorption of 10-4 could be verified experimentally, with the sensitivity to date being limited only by insufficient gain on the 2f-frequency channel. Using the offset in the 1f signal as a transmission ‘probe’, we could show that the 2f-signal can be transmission-corrected by a simple division by the 1f-background, proving that DFS-WMS provides the possibility of compensating for transmission fluctuations. With the inherent suppression of additive noise, DFS-WMS seems well suited for quantitative in situ absorption spectroscopy in large combustion systems. This assumption is supported by the first measurements of oxygen in a high-pressure combustor at 12 bar.

Real-Time Digital Image Stabilization Using Kalman Filters

Abstract: This paper presents a novel, real-time stabilization system that uses Kalman filters to remove short-term image fluctuations with retained smooth gross movements. The global camera motion is defined in terms of constant acceleration motion and constant velocity motion models, and Kalman filtering is employed to facilitate smooth operation. It is shown that the process noise variance has a direct effect on stabilization performance, and that it is possible to implement an efficient and robust stabilization system by adaptively changing the process noise variance value according to long-term camera motion dynamics.

Surface profile measurement

Abstract: An imaging system has a transmission system (2) for transmitting a modulated optical signal and a reception system (3) for receiving a received optical signal which is a reflected and delayed version of the transmitted signal. The reception system includes a controllable shutter arrangement for allowing reception in a controllable time window. A memory (4) collects reception data derived from different time windows, and a measure of distance is obtained corresponding to a maximum correlation between the received optical signal and the timing of the controllable time window. Surface profile information is derived from multiple distance measurements. The shutter arrangement enables the distance measurement (and the subsequent profile calculation) to be free from noise from other scattering sources.

Receiver window design for multicarrier communication systems

Abstract: Multicarrier modulation formats have been chosen for some wireline and wireless communication systems. These systems use the Fourier transform to convert a convolutive channel into multiple memoryless subchannels, which allows for simple equalization at the receiver. However, because the received signal is windowed in time, noise is spread between subchannels. As a result, narrowband interference sources can degrade the performance over a large number of subchannels. Receiver windowing has been proposed as a computationally efficient technique for reducing noise spreading in multicarrier communication systems. We propose a receiver window design algorithm which minimizes the noise power of the demodulated multicarrier signal. Simulations demonstrate the effectiveness of the windows on a variety of different channels and noise sources.

A Hybrid Least-Squares GA Based Algorithm for Harmlonic Estimation

Abstract: Harmonic estimation in a distorted signal along with additive noise has been an area of interest for researchers in many disciplines of science and engineering. This paper presents a new algorithm to estimate the harmonics in power systems using genetic algorithms (GAs). The harmonic estimation problem is linear in amplitude and nonlinear in phase. The proposed hybrid algorithm takes advantage of this structure and iterates between linear least squares amplitude estimation and the nonlinear GA-based phase estimation. Improvement in both convergence for solution as well as processing time is demonstrated from this algorithm.

Photoplethysmograph signal-to-noise line enhancement

Abstract: A ring plethysmograph having a pressure adjustment for locally pressurizing one side of a finger thereby biasing the pressure on an artery wall so that the plethysmograph is optimally sensitive without interfering with blood flow. An auxiliary photodetector, possibly with a second light source, is disposed on the low-pressure side of the finger for two purposes: providing a noise reference for canceling noise on the plethysmograph signal, and also for providing a separate motion signal for monitoring the activity level of a patient.

Cmos image sensor with noise cancellation

Abstract: An image sensor (10) that has one or more pixels within a pixel array (12). The pixel array may be coupled to a control circuit (20) and one or more subtraction circuits (56). The control circuit may cause each pixel to provide a first reference output signal and a reset output signal. The control circuit may then cause each pixel to provide a light response output signal and a second reference output signal. The light response output signal corresponds to the image that is to be captured by the sensor. The subtraction circuit may provide a difference between the reset output signal and the first reference output signal to create a noise signal that is stored in memory. The subtraction circuit may also provide a difference between the second reference output signal and the light response output signal to create a normalized light response output signal. The noise signal may then be subtracted from the normalized light response output signal to generate the output data of the sensor. The second reference output signal is the same as the first reference output signal so that the process in essence subtracts the reset noise from the light response signal.