Showing papers on "Impulse response published in 1998"

Range dependence of the response of a spherical head model

Abstract: The head-related transfer function (HRTF) varies with range as well as with azimuth and elevation. To better understand its close-range behavior, a theoretical and experimental investigation of the HRTF for an ideal rigid sphere was performed. An algorithm was developed for computing the variation in sound pressure at the surface of the sphere as a function of direction and range to the sound source. The impulse response was also measured experimentally. The results may be summarized as follows. First, the experimental measurements were in close agreement with the theoretical solution. Second, the variation of low-frequency interaural level difference with range is significant for ranges smaller than about five times the sphere radius. Third, the impulse response reveals the source of the ripples observed in the magnitude response, and provides direct evidence that the interaural time difference is not a strong function of range. Fourth, the time delay is well approximated by well-known ray-tracing formula due to Woodworth and Schlosberg. Finally, except for this time delay, the HRTF for the ideal sphere appears to be minimum-phase, permitting exact recovery of the impulse response from the magnitude response in the frequency domain.

Image enhancement in optical coherence tomography using deconvolution

Abstract: The present invention provides an improved optical coherence tomography system and involves estimating the impulse response (which is indicative of the actual reflecting and scattering sites within a tissue sample) from the output interferometric signal of an interferometer according to the following steps: (a) acquiring auto-correlation data from the interferometer system; (b) acquiring cross-correlation data from the interferometer system having the biological tissue sample in the sample arm; and (c) processing the auto-correlation data and the cross correlation data to produce an optical impulse response of the tissue The impulse response may be obtained from the cross-correlation and auto-correlation data by: (d) obtaining an auto-power spectrum from the auto-correlation data by performing a Fourier transform on the auto-correlation data; (e) obtaining a cross-power spectrum from the cross-correlation data by performing a Fourier transform on the cross-correlation data; (f) obtaining a transfer function of the LSI system by taking a ratio of the cross-power spectrum to the auto-power spectrum; and (g) obtaining the optical impulse response of the LSI system by performing an inverse-Fourier transform on the transfer function Preferably, coherent demodulation is used in combination with the above deconvolution technique to resolve closely-spaced reflecting sites in the sample By utilizing both the magnitude and phase data of the demodulated interferometric signals, the OCT system of the present invention is able to distinguish between closely spaced reflecting sites within the sample

Signal processing and linear systems

Abstract: BACKGROUND B1 Complex Numbers B2 Sinusoids B3 Sketching Signals B4 Cramer's Rule B5 Partial Fraction Expansion B6 Vectors and Matrices B7 Miscellaneous CHAPTER 1 INTRODUCTION TO SIGNALS AND SYSTEMS 11 Size of a Signal 12 Classification of Signals 13 Some Useful Signal Operations 14 Some Useful Signal Models 15 Even and Odd Functions 16 Systems 17 Classification of Systems 18 System Model: Input-Output Description CHAPTER 2 TIME-DOMAIN ANALYSIS OF CONTINUOUS-TIME SYSTEMS 21 Introduction 22 System Response to Internal Conditions: Zero-Input Response 23 The Unit Impulse Response h(t) 24 System Response to External Input: Zero-State Response 25 Classical Solution of Differential Equations 26 System Stability 27 Intuitive Insights into System Behavior 28 Appendix 21: Determining the Impulse Response CHAPTER 3 SIGNAL REPRESENTATION BY FOURIER SERIES 31 Signals and Vectors 32 Signal Comparison: Correlation 33 Signal Representation by Orthogonal Signal Set 34 Trigonometric Fourier Series 35 Exponential Fourier Series 36 Numerical Computation of D[n 37 LTIC System response to Periodic Inputs 38 Appendix CHAPTER 4 CONTINUOUS-TIME SIGNAL ANALYSIS: THE FOURIER TRANSFORM 41 Aperiodic Signal Representation by Fourier Integral 42 Transform of Some Useful Functions 43 Some Properties of the Fourier Transform 44 Signal Transmission through LTIC Systems 45 Ideal and Practical Filters 46 Signal Energy 47 Application to Communications: Amplitude Modulation 48 Angle Modulation 49 Data Truncation: Window Functions CHAPTER 5 SAMPLING 51 The Sampling Theorem 52 Numerical Computation of Fourier Transform: The Discrete Fourier Transform (DFT) 53 The Fast Fourier Transform (FFT) 54 Appendix 51 CHAPTER 6 CONTINUOUS-TIME SYSTEM ANALYSIS USING THE LAPLACE TRANSFORM 61 The Laplace Transform 62 Some Properties of the Laplace Transform 63 Solution of Differential and Integro-Differential Equations 64 Analysis of Electrical Networks: The Transformed Network 65 Block Diagrams 66 System Realization 67 Application to Feedback and Controls 68 The Bilateral Laplace Transform 69 Appendix 61: Second Canonical Realization CHAPTER 7 FREQUENCY RESPONSE AND ANALOG FILTERS 71 Frequency Response of an LTIC System 72 Bode Plots 73 Control System Design Using Frequency Response 74 Filter Design by Placement of Poles and Zeros of H(s) 75 Butterworth Filters 76 Chebyshev Filters 77 Frequency Transformations 78 Filters to Satisfy Distortionless Transmission Conditions CHAPTER 8 DISCRETE-TIME SIGNALS AND SYSTEMS 81 Introduction 82 Some Useful Discrete-Time Signal Models 83 Sampling Continuous-Time Sinusoids and Aliasing 84 Useful Signal Operations 85 Examples of Discrete-Time Systems CHAPTER 9 TIME-DOMAIN ANALYSIS OF DISCRETE-TIME SYSTEMS 91 Discrete-Time System Equations 92 System Response to Internal Conditions: Zero-Input Response 93 Unit Impulse Response h[k] 94 System Response to External Input: Zero-State Response 95 Classical Solution of Linear Difference Equations 96 System Stability 97 Appendix 91: Determining Impulse Response CHAPTER 10 FOURIER ANALYSIS OF DISCRETE-TIME SIGNALS 101 Periodic Signal Representation by Discrete-Time Fourier Series 102 Aperiodic Signal Representation by Fourier Integral 103 Properties of DTFT 104 DTFT Connection with the Continuous-Time Fourier Transform 105 Discrete-Time Linear System Analysis by DTFT 106 Signal Processing Using DFT and FFT 107 Generalization of DTFT to the Z-Transform CHAPTER 11 DISCRETE-TIME SYSTEM ANALYSIS USING THE Z-TRANSFORM 111 The Z-Transform 112 Some Properties of the Z-Transform 113 Z-Transform Solution of Linear Difference Equations 114 System Realization 115 Connection Between the Laplace and the Z-Transform 116 Sampled-Data (Hybrid) Systems 117 The Bilateral Z-Transform CHAPTER 12 FREQUENCY RESPONSE AND DIGITAL FILTERS 121 Frequency Response of Discrete-Time Systems 122 Frequency Response From Pole-Zero Location 123 Digital Filters 124 Filter Design Criteria 125 Recursive Filter Design: The Impulse Invariance Method 126 Recursive Filter Design: The Bilinear Transformation Method 127 Nonrecursive Filters 128 Nonrecursive Filter Design CHAPTER 13 STATE-SPACE ANALYSIS 131 Introduction 132 Systematic Procedure for Determining State Equations 133 Solution of State Equations 134 Linear Transformation of State Vector 135 Controllability and Observability 136 State-Space Analysis of Discrete-Time Systems ANSWERS TO SELECTED PROBLEMS SUPPLEMENTARY READING INDEX Each chapter ends with a Summary

Modulation Transfer Function

Abstract: 2.1 Introduction An optical system's image quality can be characterized in the spatial domain using the impulse response (spot size) of the system, or in the spatial-frequency domain using the Fourier transform of the impulse response, the transfer function. An ideal system would form a point image of a point object. But, because of diffraction and aberrations, a real system has an impulse response of nonzero width. The impulse response of a system is the two-dimensional image formed in response to a delta-function object, and is denoted by the symbol h(x,y). The actual image, g, formed by the system is the ideal image, f (an exact replica of the object with appropriate size scaling), convolved with the impulse response, h: f(x,y)**h(x,y)=g(x,y), where the double asterisk denotes a two-dimensional convolution. A narrower impulse response gives better image quality than a wide impulse response. Alternately, we can consider the imaging process in the spatial-frequency domain. In this context, we are concerned with the imaging of sinusoids of different frequencies, rather than the imaging of point objects. The irradiance distribution of an object can be thought of as composed of "spatial frequency" components, in the same way as a time-domain electrical signal is composed of various temporal frequencies by means of a Fourier analysis. First, consider an irradiance distribution as a function of x and y, as seen in Fig. 2.1. This irradiance distribution can represent either an object or an image. From a one-dimensional profile of the distribution, we obtain a single-variable function that can be Fourier decomposed into its constituent spatial frequencies (cycles/mm).

Time-Domain Analysis of Large-Amplitude Vertical Ship Motions and Wave Loads

Abstract: The vertical motions and wave induced loads on ships with forward speed are studied in the time domain, considering non-linear effects associated with large amolitude motions and hull flare shape. The method is based on a strip theory, using singularities distributed on the cross sections which satisfy the linear free surface condition. The solution is obtained in the time domain using convolution to account for the memory effects related to the free surface oscillations. In this way the linear radiation forces are represented in terms of impulse response functions, infinite frequency added masses and radiation restoring coefficients. The diffraction forces associated with incident wave scattering are linear. The hydrostatic and Froude-Krylov forces are evaluated over the instantaneous wetted surface of the hull to account for the large amplitude motions and hull flare. The radiation contribution for wave loads is also obtained in the time domain usine convolution to account for the memory effects related to the free surface oscillations. Results of motions and wave loads for the S175 container ship are presented and analyzed. The results from the present method are compared with linear results.

Frequency-Domain Karhunen -Loeve Method and Its Application to Linear Dynamic Systems

Abstract: Forthee rsttime,theKarhunen ‐Loeve(KL)procedureisderivedinthefrequencydomainasatoolforcalculating eigenmodes of linear systems. The new derivation is based on the discrete Fourier transform representation of a time average of proe le energy including a proper system response and a proe le function. Taking the variational problem posed as such with respect to the proe le function leads to an eigenformulation in the frequency domain. Choice of a system response for efe cient KL mode calculation and construction of reduced-order systems using the KL eigenmodes are also discussed. To demonstrate themethod, both mechanical and e uid dynamic models are considered. The method is equally useful in extracting eigenmodes of an experimentally generated database. Nomenclature c = wing chord length F = snapshot matrix as dee ned in Eq. (13) F = Fourier operator GIk = impulse response for the kth input GSk = step response for the kth input i

Pipeline Leak Detection by Impulse Response Extraction

Abstract: A system's response to an impulse can be used to detect and diagnose abnormalities. The impulse response can be extracted by using cross-correlations between a low amplitude pseudo random binary disturbance input and the system's output. This fact is applied to pipeline hydraulics as a means of real-time non-interruptive integrity monitoring. A method of generating the pseudo random binary disturbance is proposed. The extraction of a pipeline's impulse response with the presence of noise is investigated. The features of the response of an intact pipeline and characteristic changes in the impulse response as a result of a leak are established. The feasibility of using impulse response to detect and to locate a leak in real-time is demonstrated.

h-gamma: an RC delay metric based on a gamma distribution approximation of the homogeneous response

Abstract: Recently a probability interpretation of moments was proposed as a compromise between the Elmore delay and higher order moment matching for RC timing estimation (Kay and Pileggi, 1998). By modeling RC impulses as time-shifted incomplete gamma distribution function, the delays could be obtained via table lookup using a gamma integral table and the first three moments of the impulse response. However, while this approximation works well for many examples, it struggles with responses when the metal resistance becomes dominant, and produces results with impractical time shift values In this paper the probability interpretation is extended to the circuit homogeneous response, without requiring the time shift parameter. The gamma distribution is used to characterize the normalized homogeneous portion of the step response. For a generalized RC interconnect model (RC tree or mesh), the stability of the homogeneous-gamma distribution model is guaranteed. It is demonstrated that when a table model is carefully constructed, the h-gamma approximation provides for excellent improvement over the Elmore delay in terms of accuracy, with very little additional cost in terms of CPU time.

PRIMO: probability interpretation of moments for delay calculation

Abstract: Moments of the impulse response are widely used for interconnect delay analysis, from the explicit Elmore delay (first moment of the impulse response) expression, to moment matching methods which create reduced order transimpedance and transfer function approximations. However, the Elmore delay is fast becoming ineffective for deep submicron technologies, and reduced order transfer function delays are impractical for use as early-phase design metrics or as design optimization cost functions. This paper describes an approach for fitting moments of the impulse response to probability density functions so that delays can be estimated from probability tables. For RC trees it is demonstrated that the incomplete gamma function provides a provably stable approximation. The step response delay is obtained from a one-dimensional table lookup.

Extraction of Impulse Response Data via Wavelet Transform for Structural System Identification

Abstract: This paper presents a wavelet transform-based method of extracting the impulse response characteristics from the measured disturbances and response histories of linear structural dynamic systems. The proposed method is found to be effective in determining the impulse response functions for systems subjected to harmonic (narrow frequency-band) input signals and signals with sharp discontinuities, thus alleviating the Gibbs phenomenon encountered in FFT methods. When the system is subjected to random burst input signals for which the FFT methods are known to perform well, the proposed wavelet method performs equally well with a fewer number of ensembles than FFT-based methods. For completely random input signals, both the wavelet and FFT methods experience difficulties, although the wavelet method appears to perform somewhat better in tracing the fundamental response modes.

Equalizer for use in multi-carrier modulation systems

Abstract: The present invention provides an optimal procedure for determining in the time domain equalizer coefficients for an equalizer, where the equalizer compensates for the effects of the communications channel on the transmitted signal. A unit pulse is transmitted over the communications channel, and a channel impulse response is estimated from the received signal. A cost function establishes a mean-square error associated with the estimated channel impulse response as compared to a desired impulse response signal. The value of the cost function varies based upon an offset value between the estimated channel impulse response and an equalized channel impulse response. Values of the cost function are determined for different offsets, and the offset that produces the smallest cost function value (corresponding to the minimum mean-square error) is selected. The optimal equalizer coefficients are then calculated using the selected offset and the established cost function. In a preferred embodiment, the invention is applied to multicarrier modulation systems. Moreover, the cost function is defined as a krakovian function that depends on the offset value. That krakovian function includes a first krakovian which uses the channel impulse response and a second krakovian which uses the autocorrelation of the channel impulse response. Using the first and second krakovians and the selected offset corresponding to the minimal value of the established cost function, the optimal equalizer coefficients are determined in a straightforward, one step calculation.

Assessment of achievable PI control performance for linear processes with dead time

Abstract: A numerical scheme is outlined for the estimation of achievable PI control performance measured by output variance in linear processes with dead time when stochastic load disturbances are affecting the process For this numerical scheme, an approximate stochastic realization is employed for disturbance model identification, and this realized model is then used for the achievable performance prediction The approximate stochastic disturbance model realization is performed based on the feedback invariant closed-loop impulse response coefficients so that the impulse response coefficients of the realized disturbance model are approximately equal to a given feedback invariant impulse response sequence A computer simulation is carried out for the estimation of achievable PI control performance, and the result is compared to the true PI control performance bound

Modified Monte Carlo scheme for high-efficiency simulation of the impulse response on diffuse IR wireless indoor channels

Abstract: A modified Monte Carlo method to calculate multipath dispersion due to wall reflections on indoor wireless diffuse optical channels is presented. As with other Monte Carlo methods, it allows evaluation of not only the Lambertian but also specular reflections and can be used to validate previous simulation schemes. The main difference is that for each ray traced and for each rebound, a contribution to the receiver is calculated. This leads to a faster and more accurate simulation.

Evaluating EM waveforms by singular‐value decomposition of exponential basis functions

Abstract: Exponential basis functions preconvolved with the system waveform are used to convert measured transient decays to an ideal frequency-domain response that can be modeled more easily than arbitrary waveform data. Singular-value decomposition (SVD) of the basis functions are used to assess which specific EM waveform provides superior resolution of a range of exponential time constants that can be related to earth conductivities. The pulse shape, pulse length, transient sampling scheme, noise levels, and primary field removal used in practical EM systems all affect the resolution of time constants. Step response systems are more diagnostic of long time constants, and hence good conductors, than impulse response systems. The limited bandwidth of airborne EM systems compared with ground systems is improved when the response is sampled during the transmitter on time and gives better resolution of short time constants or fast decays.

A novel across-track SAR interferometry simulator

Abstract: A novel across-track interferometric synthetic aperture radar (SAR) raw signal simulator is presented. It is based on an electromagnetic backscattering model of the scene and an accurate description of the SAR system impulse response function. A set of meaningful examples are also presented. They show that the proposed simulator is structurally consistent and correctly simulates the decorrelation effect, both in the mean and in the distribution sense.

Monte Carlo calculation of impulse response on diffuse IR wireless indoor channels

Abstract: A method to calculate multipath dispersion owing to wall reflections on indoor wireless diffuse optical channels using Monte Carlo simulation is presented. It allows evaluation of not only Lambertian but also specular reflections, and can be used to validate previous simulation schemes. It can be extended for Lambertian (with modal number 1 or higher) or non-Lambertian light sources.

Speech processing method and apparatus for improving speech quality and speech recognition performance

Abstract: A speech processing apparatus which, in the process of performing echo canceling by using a pseudo acoustic echo signal, continuously uses an impulse response used for the previous frame as an impulse response to generate the pseudo acoustic echo signal when a voice is contained in the microphone input signal, and which uses a newly updated impulse response when a voice is not contained in the microphone input signal.

Optimal impulse response shortening for discrete multitone transceivers

Abstract: The authors have derived a new algorithm for the optimal shortening of a channel impulse response in discrete multitone (DMT) transceivers. This algorithm uses eigenvalues and eigenvectors to generate the coefficients of the shortening impulse response filter (SIRF). In comparison with the previous approach, this new algorithm can calculate the optimal settings of an SIRF with arbitrary length.

Impulse response evaluation of drilled shafts

Abstract: A test section was constructed at the National Geotechnical Experimentation Site at Northwestern University to assess the applicability of nondestructive testing methods to evaluate deep foundations under inaccessible-head conditions. Tests were performed in both the accessible and the inaccessible conditions to evaluate the effects of intervening structure. This paper focuses on the results of impulse response tests performed on the National Geotechnical Experimentation Site drilled shafts before the pile caps were constructed, i.e., in an accessible-head condition. Based on field experimentation and numerical simulations, the use of impulse response tests to identify lengths of accessible-head shafts is limited primarily by the \iL/\iD ratio of the shaft, the ratio of the shear-wave velocity of the soil to the propagation velocity of the concrete, and soil stratigraphy. The length of a drilled shaft can be found to within ±5% based solely on errors in assumed propagation velocities. Site-specific construction procedures may be important when interpreting the results of impulse response tests because the soil immediately adjacent to a shaft has a large effect on the resolution of the signals in a mobility plot.

Seismic wavelet estimation: a frequency domain solution to a geophysical noisy input-output problem

Abstract: In seismic reflection prospecting for oil and gas a key step is the ability to estimate the seismic wavelet (impulse response) traveling through the Earth. Such estimation enables filters to be designed to deblur the recorded seismic time series and allows the integration of "downhole" and surface seismic data for seismic interpretation purposes. An appropriate model for the seismic time series is a noisy-input/noisy-output linear model. The authors tackle the estimation of the impulse response in the frequency domain by estimating its frequency response function. They use a novel approach where multiple coherence analysis is applied to the replicated observed output series to estimate the output signal-to-noise ratio (SNR) at each frequency. This, combined with an estimate of the ordinary coherence between observed input and observed output, and with the spectrum of the observed input and cross-spectrum of the observed input and output, enables estimation of the frequency response function. The methodology is seen to work well on real and synthetic data.

Spectrally constrained impulse shortening filter for a discrete multi-tone receiver

Abstract: A channel in a multiple carrier communication system is equalized by computing a target spectral response, shortening the impulse response of the channel so that a significant part of an energy of the impulse response is confined to a region that is shorter than a target length and filtering the signal based on the target spectral response.

Method of and an apparatus for training tap coefficients of an adaptive equalizer

Abstract: For training tap coefficients of an adaptive equalizer of L taps to be used for equalizing an impulse response of a transmission channel ( 200 ) to be shorter than v taps, stably and speedily, a training circuit comprises: a transmitter ( 100 ) for transmitting a transmission signal (x(D)) produced by converting a frequency-domain transmission vector (X) encoded with a PRBS into a time-domain; a target-impulse-response update means ( 1300 ) for producing an updated target impulse response (B u ) making use of frequency-domain division method referring to windowed tap coefficients (w w (D)), a reception signal (y(D)), and a training vector (X) encoded with a replica of the PRBS; a target-impulse-response windowing means ( 1400 ) for outputting a windowed target impulse response (B w ) together wit a normalization coefficient (S) by windowing and normalizing the updated target impulse response (B u ) within L taps in a time-domain; a tap-coefficient update means ( 2500 ) for updating the windowed tap coefficients (w w (D)) making use of a frequency-domain LMS method referring to the normalization coefficient (S), the windowed target impulse response (B w ), the training vector (X′) and the reception signal (y(D)); and a tap-coefficient windowing means ( 1600 ) for windowing the updated tap coefficients into v taps. By updating the windowed tap coefficients (w w (D)) repeatedly until a certain convergence condition is attained, the windowed tap coefficients (w w (D)) are outputted as the tap coefficients of the adaptive equalizer.

Time Resolved Measurements Which Isolate the Mechanisms Responsible for Terahertz Glory Scattering from Dielectric Spheres

Abstract: The surface-wave scattering processes responsible, in part, for the optical glory have never been compared with theoretical predictions Here, THz impulse ranging is used to measure the time domain impulse response of spherical targets with sufficiently high temporal resolution to permit the surfacewave contribution to the total impulse response to be isolated The first direct experimental comparison for the surface wave with Mie theory as well as the surface-wave approximation of van de Hulst is performed Interference of the surface waves from a dielectric sphere is shown to lead to the frequency and angular intensity dependence of the THz glory [S0031-9007(97)04970-3] PACS numbers: 4225Fx

Halfband filters and Hilbert transformers

Abstract: This paper presents in summarizing form a description of halfband filters and the related symmetrical Hilbert transformers. It starts with the two complemetary relations by which halfband filters are defined and the consequences for their impulse responses. The idealized versions of the frequency responses of halfband lowpasses and Hilbert transformers are introduced, and the related tolerance schemes that realized systems must satisfy are described. Using their frequency responses, the transformation of one filter type into the other is presented in general form. The design of finite impulse response (FIR)-halfband filters and their relation to corresponding Hilbert transformers are recalled, using maximally flat and Chebyshev approximations as examples. It is shown that the relation between both types of systems can be used for the infinite impulse response (IIR) case as well. The design of IIR-halfband filters is presented for systems with approximately linear phase and for those with minimum phase again for maximally flat and Chebyshev approximations. The design methods are partly new. The general procedure for the transformation into Hilbert transformers yields noncausal solutions, one of which is already known from the literature. By modifying this operation, phase-splitting systems are obtained, one of them related to corresponding continuous ones, discussed in papers published around 1950. Another system with approximately linear phase corresponds to a paper presented in 1987. Finally, the coupled form of these phase splitting allpasses is found to be a Hilbert transformer with precise phase difference, but with deviations of the magnitudes of the frequency responses.

Stability impulse control of faulted nonlinear systems

Abstract: This paper presents the impulse control approach intended to urgently return to the stability basin the system states affected by abrupt changes in certain system coefficients on a short time interval. Because of its short duration, the modeling of both the fault and controller involves /spl delta/-functions significantly simplifying analysis and control of fault phenomena. The design of an impulse controller is based on the technique for computing fault-induced jumps of the system states, which is described in the paper. A sample impulse controller instantaneously returning states of a Van-der-Pol system to the stability basin is designed.