Showing papers on "Impulse response published in 2002"

Linear System Theory

Abstract: Chapter 8 establishes the relationship between the input and output power spectral densities of a linear system. Limitations on results are carefully detailed and the case of oscillator noise is considered. The theory is extended to multiple input-multiple output systems.

Comparison of different impulse response measurement techniques

Abstract: The impulse response of an acoustical space or transducer is one of its most important characterizations. In order to perform the measurement of their impulse responses, four of the most suitable methods are compared: MLS (maximum-length sequence), IRS (inverse repeated sequence), time-stretched pulses, and SineSweep. These methods have already been described in the literature. Nevertheless, the choice of one of them depending on the measurement conditions is critical. Therefore an extensive comparison has been realized. This comparison was done through the implementation and realization of a complete, fast, reliable, and cheap measurement system. Finally, a conclusion for the use of each method according to the principal measurement conditions is presented. It is shown that in the presence of nonwhite noise, the MLS and IRS techniques seem to be more accurate. On the contrary, in quiet environments the logarithmic SineSweep method seems to be the most appropriate.

Solving Dynamic Equilibrium Models by a Method of Undetermined Coefficients

Abstract: I present an undetermined coefficients method for obtaining a linear approximating to the solution of a class of dynamic, rational expectations models. I also show how that solution can be used to compute a model's implications for impulse response functions and for second moments.

Spatial resolution properties of penalized-likelihood image reconstruction: space-invariant tomographs

Abstract: This paper examines the spatial resolution properties of penalized-likelihood image reconstruction methods by analyzing the local impulse response. The analysis shows that standard regularization penalties induce space-variant local impulse response functions, even for space-invariant tomographic systems. Paradoxically, for emission image reconstruction, the local resolution is generally poorest in high-count penalties depends on the object only through its projections. This analysis leads naturally to a modified regularization penalty that leads naturally to a modified regularization penalty that yields reconstructed images with nearly uniform resolution. The modified penalty also provides a very practical method for choosing the regularization parameter to obtain a specified resolution in images reconstructed by penalized-likelihood methods.

Prediction of Mobile Radio Channels : Modeling and Design

Abstract: Prediction of the rapidly fading envelope of a mobile radio channel enables a number of capacity improving techniques like fast resource allocation and fast link adaptation. This thesis deals with linear prediction of the complex impulse response of a channel and unbiased quadratic prediction of the power. The design and performance of these predictors depend heavily on the correlation properties of the channel. Models for a channelwhere the multipath is caused by clusters of scatterers are studied. The correlation for the contribution from a cluster can be approximated as a damped complex sinusoid. A suitable model for the dynamics of the channel is an ARMA-process. This motivates the use of linear predictors.A limiting factor in the prediction are the estimation errors on the observed channels. This estimation error, caused by measurement noise and time variation, is analyzed for a block based least squares algorithm which operates on a Jakes channel model. Efficient noise reduction on the estimated channel impulse responses can be obtained with Wienersmoothers that are based on simple models for the dynamics of the channel combined with estimates of the variance of the estimation error.Power prediction that is based on the squared magnitude of linear prediction of the taps will be biased. Hence, a bias compensated power predictor is proposed and the optimal prediction coefficients are derived for the Rayleigh fading channel. The corresponding probability density functions for the predicted power are also derived. A performance evaluation of the prediction algorithm is carried out on measured broadband mobile radio channels. The performance is highly dependent on the variance of the estimation error and the dynamics of the individual taps.

Communication system and methods of estimating channel impulse responses therein

Abstract: Multiple Steiner codes are transmitted as bursts from multiple base stations (182, 184, 186) having one or more transmit elements (174, 176, 178, 180), with successive bursts providing an extended training sequence for use in channel estimation at an addressed unit (172), such as a mobile handset Accurate channel estimation is possible through the use of Wiener frequency domain MMSE deconvolution (518) combined with frequency domain spatial decoupling matrices, with quasi-orthogonal pseudo-noise sequences (502, 504, 520, 522) allocated to base stations and their antenna elements The use of Steiner codes to supplement Wiener frequency domain MMSE deconvolution and frequency domain spatial decoupling results in the possibility of allocating only a single training sequence to each base station provided that the training sequence is of sufficient length to encompass all multiple time-translated channel impulse responses (H) Estimates may be refined iteratively by minimising the MS error of demodulated pilot symbols Estimates may also be refined by removing taps from the impulse response which are insignificant based on a relatively long-term power-delay profile for the channel

Fractional Calculus via Functional Calculus: Theory and Applications

Abstract: This paper demonstrates the power of the functional-calculus definition of linear fractional (pseudo-) differential operators via generalised Fourier transforms. Firstly, we describe in detail how to get global causal solutions of linear fractional differential equations via this calculus. The solutions are represented as convolutions of the input functions with the related impulse responses. The suggested method via residue calculus separates an impulse response automatically into an expo- nentially damped (possibly oscillatory) part and a 'slow' relaxation. If an impulse response is stable it becomes automatically causal, otherwise one has to add a homogeneous solution to get causality. Secondly, we present examples and, moreover, verify the approach along experiments on viscolelastic rods. The quality of the method as an effective few-parameter model is impressively demonstrated: the chosen reference example PTFE (Teflon) shows that in contrast to standard classical models our model describes the behaviour in a wide frequency range within the accuracy of the measurement. Even dispersion effects are included. Thirdly, we conclude the paper with a survey of the required theory. There the attention is directed to the extension from the L2-approach on the space of distributions D � .

Iterative site-based modeling for wireless infrared channels

Abstract: We describe an iterative site-based method for estimating the impulse response of wireless infrared channels. The method can efficiently account for multiple reflections of any order. A simple geometrical model of indoor environments is presented which includes interior features such as partitions, people, and furniture, thus permitting accurate evaluation of shadowing effects. For a reflection order of three, the iterative method is over 90 times faster than the existing recursive technique. A computer implementation is described and used to demonstrate the efficiency and accuracy of the method.

Transfer function-noise modeling in continuous time using predefined impulse response functions

Abstract: Received 18 December 2001; revised 1 August 2002; accepted 1 August 2002; published 11 December 2002. [1] A method of transfer function-noise (TFN) modeling is presented that operates in continuous time and uses a predefined family of impulse response (IR) functions. The resulting class of models is referred to as predefined IR function in continuous time (PIRFICT). It provides a useful tool for standardized analysis of time series, as it can be calibrated using irregularly spaced data and does not require a model identification phase prior to calibration. In section 2, the discrete Box-Jenkins (BJ) model is presented and transformed into continuous time to obtain the PIRFICT model. The discrete transfer function of a BJ model, which is made up of a variable number of parameters, is replaced by a simple analytical expression that defines the IR function. From the IR function, block response functions are derived that enable the model to handle irregularly spaced data. In the example application, the parameter estimates and performance of the BJ and PIRFICT model are compared using a data set of 15 piezometers and a simulated series. It was found that the estimated transfer and BR functions of both models follow the same general pattern, although the BJ transfer functions are partly irregular. The performance of both models proves to be highly comparable for all piezometers. INDEX TERMS: 1829 Hydrology: Groundwater hydrology; 1833 Hydrology: Hydroclimatology; 1854 Hydrology: Precipitation (3354); 1869 Hydrology: Stochastic processes; 9820 General or Miscellaneous: Techniques applicable in three or more fields; KEYWORDS: groundwater level fluctuations, transfer function-noise, continuous time, time series, impulse response, PIRFICT

Frequency analysis of digital holography

Abstract: A coherent optical imaging system consisting of recording a digital hologram by a CCD array and numerical reconstruction of the complex wave field in a computer is subjected to a frequency analysis. This analysis recognizes Fresnel and lensless Fourier transform holography; collimated and divergent reference waves; as well as the real image, the virtual image, and the dc term. The influences of finite sampling and the fill factor of the CCD pixels are examined. The impulse response of the system is a shifted Fraunhofer diffraction pattern of the aperture defined by the CCD. A fill factor below unity leads to a contrast decrease, which is quantitatively described in the modulation transfer function.

Detection of subsurface resistivity contrasts with application to location of fluids

Abstract: The invention relates to a method of mapping subsurface resistivity contrasts by making multichannel transient electromagnetic (MTEM) measurements on or near the earth's surface using at least one source, receiving means for measuring the system response and at least one receiver for measuring the resultant earth response. All signals from the or each source-receiver pair are processed to recover the corresponding electromagnetic impulse response of the earth and such impulse responses, or any transformation of such impulse responses, are displayed to create a subsurface representation of resistivity contrasts. The invention enables subsurface fluid deposits to be located and identified and the movement of such fluids to be monitored.

Stochastic approximation in nonparametric identification of Hammerstein systems

Abstract: Derived from the idea of stochastic approximation, recursive algorithms to identify a Hammerstein system are presented. Two of them recover the characteristic of the nonlinear memoryless subsystem, while the third one estimates the impulse response of the linear dynamic part. The a priori information about both subsystems is nonparametric. Consistency in quadratic mean is shown, and the convergence rate is examined. Results of numerical simulation are also presented.

On the design and implementation of FIR and IIR digital filters with variable frequency characteristics

Abstract: This paper studies the design and implementation of finite-impulse response (FIR) and infinite-impulse response (IIR) variable digital filters (VDFs), whose frequency characteristics can be controlled continuously by some control or tuning parameters. A least squares (LS) approach is proposed for the design of FIR VDFs by expressing the impulse response of the filter as a linear combination of basis functions. It is shown that the optimal LS solution can be obtained by solving a system of linear equations. By choosing the basis functions as piecewise polynomials, VDFs with larger tuning range than that of ordinary polynomial based approach results. The proposed VDF can be efficiently implemented using the familiar Farrow structure. Making use of the FIR VDF so obtained, an Eigensystem Realization Algorithm (ERA)-based model reduction technique is proposed to approximate the FIR VDF by a stable IIR VDF with lower system order. The advantages of the model reduction approach are: 1) it is computational simple which only requires the computation of the singular value decomposition of a Hankel matrix; 2) the IIR VDF obtained is guaranteed to be stable; and 3) the frequency response such as the phase response of the FIR prototype is well preserved. Apart from the above advantages, the proposed IIR VDF does not suffer from undesirable transient response during parameter tuning found in other approaches based on direct tuning of filter parameters. For frequency selective VDFs, about 40% of the multiplications can be saved using the IIR VDFs. The implementation of the proposed FIR VDF using sum-of-powers-of-two (SOPOT) coefficient and the multiplier block (MB) technique are also studied. Results show that about two-third of the additions in implementing the multiplication of the SOPOT coefficients can be saved using the multiplier block, which leads to significant savings in hardware complexity.

Time domain analysis of grounding electrodes impulse response

Abstract: Lightning protection studies require estimation of grounding systems' dynamic behavior. This paper presents the results of a new methodology for calculating the lightning response of the basic component of any grounding system, the grounding electrode. Lightning strike is modeled using a double exponential time function. Closed-form mathematical formulae are used to describe current and voltage distribution along the electrode. The effect of soil ionization can be also taken into account. The proposed methodology is validated by comparison of the obtained results with experimental and simulated waveforms found in literature.

Parallel interference cancellation receiver for multiuser detection of CDMA signals

Abstract: A parallel interference cancellation receiver that reduces impulse response interference using a model of the received signal similar to that used in block linear equalizers. Block linear equalizers comprise decorrelating receivers, zero-forcing receivers, minimum mean square error receivers and the like. The invention comprises an interference computation processor feedback loop for correcting the output of a direct interference canceller. The m iterative process removes interferers from the output symbols of a matched-filter. The PIC receiver uses received signal models of the various block linear equalizers that do not assume that each subchannel consists of several distinct paths. The receiver estimates the impulse response characteristic of each subchannel as a whole.

Maximally flat low-pass digital differentiator

Abstract: This paper describes the design of type III and type IV linear-phase finite-impulse response (FIR) low-pass digital differentiators according to the maximally flat criterion. We introduce a two-term recursive formula that enables the simple stable computation of the impulse response coefficients. The same recursive formula is valid for both Type III and Type IV solutions.

A min, + system theory for constrained traffic regulation and dynamic service guarantees

Abstract: By extending the system theory under the (min, +) algebra to the time-varying setting, we solve the problem of constrained traffic regulation and develop a calculus for dynamic service guarantees. For a constrained traffic-regulation problem with maximum tolerable delay d and maximum buffer size q, the optimal regulator that generates the output traffic conforming to a subadditive envelope f and minimizes the number of discarded packets is a concatenation of the g-clipper with g(t) = min[f(t+ d), f (t)+q] and the maximal f-regulator. The g-clipper is a bufferless device, which optimally drops packets as necessary in order that its output be conformant to an envelope g. The maximal f-regulator is a buffered device that delays packets as necessary in order that its output be conformant to an envelope f. The maximal f-regulator is a linear time-invariant filter with impulse response f, under the (min, +) algebra. To provide dynamic service guarantees in a network, we develop the concept of a dynamic server as a basic network element. Dynamic servers can be joined by concatenation, "filter bank summation," and feedback to form a composite dynamic server. We also show that dynamic service guarantees for multiple input streams sharing a work-conserving link can be achieved by a dynamic service curve earliest deadline scheduling algorithm, if an appropriate admission control is enforced.

Unbiased power prediction of Rayleigh fading channels

Abstract: Prediction of the rapidly fading envelope of a mobile radio channel enables a number of capacity improving techniques like fast resource allocation or fast adaptive modulation. Some power prediction algorithms are based on linear prediction of the taps of the complex impulse response and then forming the power prediction as the sum of the absolute square of the prediction of the taps in the impulse response. This will render a biased power predictor, that generally underestimates the power. We propose a bias compensated power predictor and derive the optimal prediction coefficients for the Rayleigh fading channel. The importance of efficient noise reduction of channel samples that are used as inputs to the predictor is also emphasized. A performance evaluation of the prediction algorithm is carried out on measured broadband mobile radio channels.

Linear Systems Theory

Abstract: This chapter contains sections titled: Linear Shift-Invariant Systems, Convolution, Impulses, Impulse Response of a System, Resistor-Capacitor Circuits, Higher Order Equations, The Heaviside-Laplace Transform, Linear System's Transfer function, The Resistor-Capacitor Circuit (A Second Look), Low-Pass, High-Pass, and Band-Pass Filters

Single-carrier to multi-carrier wireless architecture

Abstract: A Baseband receiver including a CIR estimate block, gain, phase and timing loops, a CMF, a single-carrier processor and a multi-carrier processor. The CIR estimate block generates an impulse response signal based on a receive signal that is a single-carrier signal or a single-carrier segment of a mixed carrier signal. The single-carrier segment has a spectrum that approximates a multi-carrier spectrum. The gain, phase and timing loops adjust gain, phase, frequency and timing to provide an adjusted receive signal. The CMF filters the adjusted receive signal according to the impulse response signal. The single-carrier processor processes the adjusted and filtered receive signal to resolve a single-carrier segment of a mixed carrier signal. The single-carrier processor detects a mixed carrier mode indication in a single-carrier segment and asserts a start indication. The multi-carrier processor processes a multi-carrier segment of a mixed carrier signal in response to assertion of the start indication.

Reflection model for calculation of the impulse response on IR-wireless indoor channels using ray-tracing algorithm

Abstract: This paper presents a simulation tool for the fast calculation of the impulse response on infrared (IR) wireless indoor channels. We used Phong's model to approximate the reflection pattern of the indoor surfaces upon which a Monte Carlo ray-tracing method allows us to evaluate the impulse response. We also present computer simulation results showing that the use of Phong's model can lead to differences with respect to Lambert's model in the evaluation of the impulse response when surfaces present a high specular component. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 296–300, 2002.

Recent Applications of Ultra Wideband Radar and Communications Systems

Abstract: Ultra wideband technology has its origins in the development of time-domain (impulse response) techniques for the characterization of linear, time-invariant microwave structures The advent of the time-domain sampling oscilloscope (Hewlett-Packard c 1962) and the development of techniques for subnanosecond (baseband) pulse generation provided the requisite tools for further basic research In the early 1970’s, impulse or baseband techniques were applied to a large number of potential applications ranging from low cost, high resolution radar to specialized communications systems having low probability of detection and low interference potential

Statistical modeling of small-scale fading in directional radio channels

Abstract: After a review of the known description of time-variant channels by means of system and correlation functions, a consistent extension of this description to directional time-variant channels is described. This extension allows a clear distinction between time- and space-variant effects in directional mobile radio channels. The major intention of the described directional extension however is the derivation of a statistical modeling approach for small-scale fading effects in time-variant wideband directional channels, which can be regarded as a consistent extension of the well established Rayleigh or Rice-fading approach for nondirectional time-variant narrowband channels. The approach, which is based on the time and aperture-variant transfer function, appears to be preferable to the frequently used statistical modeling of the time-variant angle-resolved impulse response for several reasons. The major advantage is that the approach can cope with the demand for a great number of superimposing components as the basis for statistical modeling. The correlation between adjacent values is proposed to be achieved by filtering with appropriate directional scattering functions. The description of the modeling approach, as done in the present paper, is intended to be general and universal; for the application on certain channel types statistical distribution functions and parameters to be used with the approach can readily be determined from appropriate measurements.

Blind, adaptive channel shortening by sum-squared auto-correlation minimization (SAM)

Abstract: We propose a new blind, adaptive channel shortening algorithm for updating a time-domain equalizer (TEQ) in a system employing multicarrier modulation The technique attempts to minimize the sum-squared auto-correlation of the combined channel-TEQ impulse response outside a window of desired length The proposed algorithm, sum-squared auto-correlation minimization (SAM), assumes the source sequence to be white and wide-sense stationary, and it is implemented as a stochastic gradient descent algorithm Simulation results demonstrating the success of the SAM algorithm are provided

Adaptive pre-equalization method and apparatus

Abstract: An adaptive pre-equalizer (15) is disclosed to compensate amplitude ripples in a low cost transmitter pass-band filter (35, 200). A filtered-x LMS algorithm is proposed to calculate the equalizer coefficients (72). To this purpose, the modulated RF signal is demodulated at the transmitter and subtracted from a filtered version of the original base band signal. The impulse response of the low-cost transmit filter (35, 200) is approximated by a delay (73). The disclosure may be applied to direct conversion or heterodyne transmitters using e.g. OFDM.

Estimation of input function and kinetic parameters using simulated annealing: application in a flow model

Abstract: Accurate determination of the input function is essential for absolute quantification of physiological parameters in positron emission tomography and single-photon emission computed tomography imaging, but it requires an invasive and tedious procedure of blood sampling that is impractical in clinical studies. We previously proposed a technique that estimates simultaneously kinetic parameters and the input function from the tissue impulse response functions and requires two blood samples. A nonlinear least squares method estimated all the parameters in the impulse response functions and the input function but failed occasionally due to high noise levels in the data, causing an ill-conditioned cost function. This paper investigates the feasibility of applying a Monte Carlo method called simulated annealing to estimate kinetic parameters in the impulse response functions and the input function. Time-activity curves of teboroxime, which is very sensitive to changes in the input function, were simulated based on published data obtained from a canine model. The equations describing the tracer kinetics in different regions were minimized simultaneously by simulated annealing and nonlinear least squares. We found that the physiological parameters obtained with simulated annealing are accurate, and the estimated input function more closely resembled the simulated curve. We conclude that simulated annealing reduces bias in the estimation of physiological parameters and determination of the input function.

Estimation of blur and noise parameters in remote sensing

Abstract: In this paper we propose a new algorithm to estimate the parameters of the noise related to the sensor and the impulse response of the optical system, from a blurred and noisy satellite or aerial image. The noise is supposed to be white, Gaussian and stationary. The blurring kernel has a parametric form and is modeled in such a way as to take into account the physics of the system (the atmosphere, the optics and the sensor). The observed scene is described by a fractal model, taking into account the scale invariance properties of natural images. The estimation is performed automatically by maximizing a marginalized likelihood, which is achieved by a deterministic algorithm whose complexity is limited to O (N), where N is the number of pixels.

UWB channel impulse response characterization using deconvolution techniques

Abstract: UWB Channels can be measured by sounding the channel with pulses, and thereby obtain the impulse response. Multipath components have different waveforms depending on the type of transmitter and receiver antennas used and the angles of transmission and reception. A modified deconvolution technique is introduced to extract the UWB channel response. The application of deconvolution techniques results in resolving multipath components with waveforms different from that of the sounding pulse. Resolving more components should improve the design of the rake receiver. Accurate characterization for the impulse response of a UWB communication system facilitates performance evaluation studies such as simulating the effect of pulse shaping.

VARs, Common Factors and the Empirical Validation of Equilibrium Business Cycle Models

Abstract: Equilibrium business cycle models have typically less shocks than variables. As pointed out by Altug, 1989, and Sargent, 1989, if variables are measured with error, this characteristic implies that the model solution for measured variables has a factor structure. This Paper compares estimation performance for the impulse response coefficients based on a VAR approximation to this class of models and an estimation method that explicitly takes into account the restrictions implied by the factor structure. Bias and mean squared error for both factor based and VAR based estimates of impulse response functions are quantified using, as a data generating process, a calibrated standard equilibrium business cycle model. We show that, at short horizons, VAR estimates of impulse response functions are less accurate than factor estimates while the two methods perform similarly at medium and long run horizons.