Input Power Spectral Density Research Articles

Optimum optical modulation index of laser transmitters in scm systems

An analysis of the optimum optical modulation index of laser transmitters in SCM systems is presented. Nonlinear distortion arising from overmodulation in a laser-limiter combination is studied. A generalised analysis, based on rectangular signal input power spectral density and broadband transmission, is given for the nonlinear noise spectral density. A computer algorithm is developed to generate the optimum modulation index which maximises the received CNR for SCM transmission.

Extension of an Itô-based general approximation technique for random vibration of a BBW general hysteris model part II: Non-Gaussian analysis

The work presented in this paper constitutes the second phase of on-going research aimed at developing mathematical models for representing general hysteretic behavior of structures and approximation techniques for the computation and analysis of the response of hysteretic systems to random excitations. In this second part, the technique previously developed by the authors for the Gaussian response analysis of non-linear systems with general hysteretic behavior is extended for the non-Gaussian analysis of these systems. This approximation technique is based on the approach proposed independently by Ibrahim and Wu-Lin. In this work up to fourth order moments of the response co-ordinates are obtained for the Bouc-Baber-Wen smooth hysteresis model. These higher order statistics previously have not been made available for general hysteresis models by using existing approximation methods. Second order moments obtained for the model by this non-Gaussian closure scheme are compared with equivalent linearization and Gaussian closure results via Monte Carlo simulation (MCS). Higher order moments are compared with the simulation results. The study performed for a wide range of degradation parameters and input power spectral density ( PSD) levels shows that the non-Gaussian responses obtained by this approach are in better agreement with the MCS results than the linearized and Gaussian ones. This approximation technique can provide information on higher order moments for general hysteretic systems. This information is valuable in random vibration and the reliability analysis of hysteretically yielding structures.

An Itô-based general approximation method for random vibration of hysteretic systems, part I: Gaussian analysis

The cumulant-neglect closure scheme independently developed by Ibrahim and Lin is extended for determining the stationary and non-stationary response of non-linear systems with hysteric restoring force characteristics. The method is applied to the analysis of a hysteresis and model with strength and/or stiffness degradation capabilities. This model has been studied in the past by Baber and Wen for the analysis of hysterically degrading systems using equivalent linearization. The same model has also been used for stochastic seismic performance evaluation of reinforced concrete buildings. Response statistics obtained for the model by using this closure scheme are compared with results of equivalent linearization via Monte Carlo simulation. The study performed, for a wide range of degradation parameters and input power spectral density levels, shows that the Gaussian responses obtained by this approach are identical with the linearized results. This general approximation technique, however, can provide information on higher order statistics for hysteretic systems. These non-Gaussian statistics have not been made available so far by the existing approximation techniques. In this paper the Gaussian statistics are presented.

ROBUST FILTERS FOR TIME DELAY ESTIMATORS WITH BOUNDED SPECTRAL CLASSES AT THE INPUTS

Optimum filters are used to enhance the performance of the generalized cross correlator (GCC) used in time delay estimators (TDE). The performance of these TDE can deteriorate considerably for deviations in the input power spectral densities (PSD's) from their assumed nominal values. In this pap-er we consider the bounded spectral classes of PSD's which are useful mode-ls when the input PSD's are not precisely known. For these classes, robust filters for TDE are derived for two optimum criterions separately. These criterions are maximizing the signal to noise ratio and minimizing the mean square error. The robust filters obtained achieve better performance for any inputs within the assumed PSD's. Numerical examples given illustrate the theoretical results.

Volterra Systems with Random Inputs: A Formalized Approach

The object of this work is to investigate the problem of Volterra systems driven by random inputs. General expressions for the second-order output statistics of a Volterra system are obtained and formalized. The input-output crosscorrelation and output autocorrelation functions are expressed in terms of higher order input autocorrelation functions. In the frequency domain, the cross-power and output power spectral densities are expressed in terms of higher order input power spectral densities. These expressions are used to obtain closed-form equations for the cross-power and output power spectral densities of a Volterra system driven by a real, stationary, zero-mean Gaussian input.

Biological system transfer-function extraction using swept-frequency and correlation techniques

The paper describes the application of a swept-frequency-system identification technique to biological systems. By linearly sweeping the frequency of the sinusoidal input signal over the range of frequencies of interest, the frequency-response profile of the biological system can be rapidly determined. System transfer characteristics are extracted from the input-power spectral density and output-input crosspower spectral-density computations. Noise, harmonic distortion and sweeptime considerations are given. Logarithmic frequencysweeping is suggested as a means of avoiding harmonic distortion.

STATISTICAL ESTIMATION OF THE MAXIMUM RESPONSE OF STRUCTURES SUBJECTED TO EARTHQUAKE MOTION

In this paper, the authors derived analytically the formula finding the absolute maximum response of structures due to earthquake motions from their respective maximum acceleration. The computation results for a given structure by this formula accompanied by the assumptions of input power spectral density gave a good coincidence within a narrow band estimation with its precise response obtained by the direct-integration of the governing equation with strong-earthquake records as an input.

Analytic inversion of a class of covariance matrices

The sample covariance matrix arising out of finite memory linear least squares estimation over a set of equally spaced time points, is inverted by spectral methods (operationally referred to as the z transform). It is shown that the complexity of the problem depends only upon the complexity of the input correlation function. The final solution is shown to reduce to the inversion of a triangular system of linear equations of an order less than half the degree of the denominator of the input power spectral density function.