localization of damaged structural connections based on experimental modal and sensitivity analysis a method for the detection of damage location for framed structures has been proposed unlike most of the existing methods the proposed method has been proven by a series of experimental case studies and found to be practical in real applications this paper reports the theoretical development of the proposed method and the verification of the method with one numerical case study by using a six storey frame and one experimental case study by using a two storey frame two techniques have been developed in this proposed method the approximate parameter change apc technique and the damage signature matching dsm technique both techniques employ measured modal data before and after the structure is damaged the combination of these two techniques forms a practical method for the detection of damage locations

sensitivity analysis for antenna near field imaging although imaging and inverse scattering problems have been thoroughly studied during the last century there is only a partial understanding of these complex problems most of the efforts have been placed on the development of efficient inversion algorithms and mathematical uniqueness results in comparison there are very few results and a limited knowledge about the information content in the inversion data in this paper we provide a mathematical framework for sensitivity analysis of antenna near field imaging problems based on the multipole expansion of the electromagnetic field and the fisher information to quantify the quality of data by exploiting this framework a fundamental relation for accuracy and resolution is formulated based on the crameacuter rao bound crb the sensitivity analysis is illustrated using a relevant example with cylindrical measurement data

the beta model maximum likelihood cramer rao bounds and hypothesis testing we study the maximum likelihood estimator in a setting where the dependent variable is a random graph and covariates are available on a graph level the model generalizes the well known beta model for random graphs by replacing the constant model parameters with regression functions cramer rao bounds are derived for special cases of the undirected beta model the directed beta model and the covariate based beta model the corresponding maximum likelihood estimators are compared with the bounds by means of simulations moreover examples are given on how to use the presented maximum likelihood estimators to test for directionality and significance finally the applicability of the model is demonstrated using temporal social network data describing communication among healthcare workers

tilting modules and tilting torsion theories abstract we generalize basic results about classical tilting modules and partial tilting modules to the infinite dimensional case over an arbitrary ring r the methods employed combine classical techniques of representation theory of finite dimensional algebras with new techniques of the theory of modules using a generalization of the bongartz lemma we characterize tilting torsion theories in mod r i e torsion theories induced by infinitely generated tilting modules we investigate lattices gen p p of torsion classes induced by partial tilting modules p applying our results to tilting torsion classes we prove a version of the brenner butler theorem and a generalization of the assem smalo theorem to the case when r is artinian

joint estimation of porosity and saturation using stochastic rock physics modeling sediment porosity and saturation affect bulk modulus shearmodulus anddensity consequently estimatinghydrocarbon saturation and reservoir porosity from seismic data is a joint estimation problem uncertainty in porosity will lead toerrorsinsaturationprediction andviceversa porosityand saturation can be jointly estimated using stochastic rockphysicsmodelingandformalbayesianestimationmethodology knowledge of shear impedance reduces the uncertainty inporosityandthusalsoreducesuncertaintyinsaturationestimation this study investigates joint estimation of porosity and saturation by using rock physics stochastic modeling and bayesian estimation theory to derive saturation and porosity maps of expected pay sands in the field example the uncertainty in porosity quantified by the standard deviation stdassociatedwiththeposteriorprobabilitydensityfunctionpdf derivedfrominversionofseismicdataismuchless than the uncertainty in the derived saturation for a typical case the std associated with saturation is 24 while porositystdisabout1 34porosityunitsgivenseismic derived inversionattributeswithreasonableaccuracy comparisonof these numbers with prior estimates showed that inversion of seismic data decreased the uncertainty in porosity to 15 of the prior uncertainty while saturation uncertainty was only reduced to 92 of the prior uncertainty although these resultsmayvaryfromonelocationtoanother themethodology isgeneralandcanbeappliedtootherlocations

limits of sensing temporal concentration changes by single cells berg and purcell biophys j 20 193 1977 calculated how the accuracy of concentration sensing by single celled organisms is limited by noise from the small number of counted molecules here we generalize their results to the sensing of concentration ramps which is often the biologically relevant situation e g during bacterial chemotaxis we calculate lower bounds on the uncertainty of ramp sensing by three measurement devices a single receptor an absorbing sphere and a monitoring sphere we contrast two strategies simple linear regression of the input signal versus maximum likelihood estimation and show that the latter can be twice as accurate as the former finally we consider biological implementations of these two strategies and identify possible signatures that maximum likelihood estimation is implemented by real biological systems

estimate of the axial force in slender beams with unknown boundary conditions using one flexural mode shape abstract this paper presents an experimental procedure for the axial load identification of slender prismatic beams with unknown boundary conditions by making use of one vibration frequency and of five amplitudes of the corresponding mode shape in fact this method does not require the knowledge of the effective length of the beam under examination but only the flexural rigidity and mass per unit length the proposed algorithm was verified by means of many numerical and experimental tests on tie rods having different boundary conditions excellent estimates of the axial forces were obtained finally the influence of the location of the instrumented sections on the estimation of the axial load was analyzed using a simply supported beam model

absorbing boundary conditions for difference approximations to the multi dimensional wave equation construction des conditions aux limites absorbantes pour l equation des ondes multidimensionnelle a l aide d approximations aux differences formulation sous forme canonique des conditions aux limites absorbantes analytiques

on the flexural vibration of cylinders under axial loads numerical and experimental study abstract the flexural vibration of a homogeneous isotropic linearly elastic cylinder of any aspect ratio is analysed in this paper natural frequencies of a cylinder under uniformly distributed axial loads acting on its bases are calculated numerically by the ritz method with terms of power series in the coordinate directions as approximating functions the effect of axial loads on the flexural vibration cannot be described by applying infinitesimal strain theory therefore geometrically nonlinear strain displacement relations with second order terms are considered here the natural frequencies of free free clamped clamped and sliding sliding cylinders subjected to axial loads are calculated using the proposed three dimensional ritz approach and are compared with those obtained with the finite element method and the bernoulli euler theory different experiments with cylinders axially compressed by a hydraulic press are carried out and the experimental results for the lowest flexural frequency are compared with the numerical results an approach based on the ritz formulation is proposed for the flexural vibration of a cylinder between the platens of the press with constraints varying with the intensity of the compression the results show that for low compressions the cylinder behaves similarly to a sliding sliding cylinder whereas for high compressions the cylinder vibrates as a clamped clamped one

robust linear channel estimation methods for per subcarrier transmit antenna selection the linear minimum mean squared error mse channel estimator for systems employing per subcarrier transmit antenna selection is developed frequency domain correlations after the selection process are shown to be approximated well using a simple function which makes near optimal channel estimation practically possible however the resultant estimators are not robust to errors in the assumed model in terms of the antenna to subcarrier assignment used at transmission as we motivate both analytically and via simulations this is an issue when the channels for conveying this information to the receiver are severely constrained we present windowed channel estimations and new robust estimation algorithms either individually or in combination as solutions to counter this sensitivity the robust estimators are developed based on the principles of 1 minimising the worst case mse over the set of possible models and 2 minimising the expected mse over the set of possible models the latter estimator is preferred due to the lower implementation complexity and better mse performance we also prove theoretical asymptotic in signal to noise ratio performances of the two estimators used with the proposed correlation model simulation results illustrate the performance gains and improved robustness offered by the developed estimators

active learning applied to rcs computations with nonuniform sampling using different objective functions an active learning framework is introduced to reduce the number of frequencies and angles one must consider for wideband monostatic scattering computations or measurements this method is used to optimally select those frequencies and angles that would be most informative resulting in nonuniform sampling and often a reduced number of points vis agrave vis uniform sampling in this paper we focus on jointly two dimensional optimal sampling in frequency and incident angle thetas for monostatic scattering the method consists of two basic steps one step involves estimation of model parameters using a least square ls algorithm the next step is to optimally choose the next point frequency and thetas for analysis by the computational model or experiment this new point is selected with the goal of reducing uncertainty in the parametric model quantified via the fisher information matrix iterating these two steps a sequence of numerical computations or measurements are performed each at the most informative point for learning the parameters of the associated simpler parametric model this idea is demonstrated here in the context of reducing the number of points frequencies and orientations at which a computational model must be employed and in order to avoid repeatedly gathering samplings at the edge of the input space an alternative objective function is applied which makes the actively selected points closer to a region of interest

a refined use of the residue theorem for the evaluation of band averaged input power into linear second order dynamic systems abstract in a recent work a strategy was proposed which exploits the residue theorem as an efficient tool for evaluating the frequency averaged input power into vibrating systems in this paper such a technique is generalised and further insight and improvements are presented evaluating band averages requires the solution of a weighted integral over a real frequency variable in this paper the integration path is moved to the complex plane where the input mobility shows a smoother behaviour consequently a smaller number of quadrature points are needed to perform an accurate integration which leads to a significant reduction of computational time in addition the connection between the use of quadrature rules in the complex plane and weighting functions on real frequencies is considered two application examples prove the accuracy of the present strategy for different quadrature rules adaptive integration schemes are also investigated

k means clustering based data detection and symbol timing recovery for burst mode optical receiver burst mode receivers are key components of optical transmission systems including passive optical networks and have received much attention in recent years we present new efficient methods for burst optical signal detection in burst mode data transmission using a modified k means clustering technique we also develop a data aided feedforward symbol timing recovery method based on a polynomial interpolation and maximum likelihood estimation theory a performance criterion considering the error caused by the interpolation approximation is derived for this method the proposed detection and timing recovery approaches can be implemented effectively and rapidly therefore they are very suitable for burst mode receivers we also provide some numerical examples to demonstrate the performance of the proposed methods

calculation of the fisher information matrix for multidimensional data sets data sets that are acquired in many practical systems can be described as the output of a multidimensional linear separable denominator system with gaussian measurement noise an important example is nuclear magnetic resonance nmr spectroscopy in nmr spectroscopy high accuracy parameter estimation is of central importance a classical result on the crame spl acute r rao lower bound states that the inverse of the fisher information matrix fim provides a lower bound for the covariance of any unbiased estimator of the parameter vector the calculation of the fim is therefore of central importance for an assessment of the accuracy with which parameters can be estimated it is shown how the fim can be expressed using the matrices that determine the system that generates the data set for uniformly sampled data it is shown how the fim can be expressed through the solutions of lyapunov equations the novel techniques are demonstrated with an example arising from nmr spectroscopy

n star modules and n tilting modules we give some characterizations of not necessarily selfsmall n star modules and prove that not necessarily finitely generated n tilting modules are precisely not necessarily selfsmall n star modules n presenting all the injectives

retinal vessel centerline extraction using multiscale matched filters confidence and edge measures motivated by the goals of improving detection of low contrast and narrow vessels and eliminating false detections at nonvascular structures a new technique is presented for extracting vessels in retinal images the core of the technique is a new likelihood ratio test that combines matched filter responses confidence measures and vessel boundary measures matched filter responses are derived in scale space to extract vessels of widely varying widths a vessel confidence measure is defined as a projection of a vector formed from a normalized pixel neighborhood onto a normalized ideal vessel profile vessel boundary measures and associated confidences are computed at potential vessel boundaries combined these responses form a six dimensional measurement vector at each pixel a training technique is used to develop a mapping of this vector to a likelihood ratio that measures the vesselness at each pixel results comparing this vesselness measure to matched filters alone and to measures based on the hessian of intensities show substantial improvements both qualitatively and quantitatively the hessian can be used in place of the matched filter to obtain similar but less substantial improvements or to steer the matched filter by preselecting kernel orientations finally the new vesselness likelihood ratio is embedded into a vessel tracing framework resulting in an efficient and effective vessel centerline extraction algorithm

adaptive image denoising by targeted databases we propose a data dependent denoising procedure to restore noisy images different from existing denoising algorithms which search for patches from either the noisy image or a generic database the new algorithm finds patches from a database that contains relevant patches we formulate the denoising problem as an optimal filter design problem and make two contributions first we determine the basis function of the denoising filter by solving a group sparsity minimization problem the optimization formulation generalizes existing denoising algorithms and offers systematic analysis of the performance improvement methods are proposed to enhance the patch search process second we determine the spectral coefficients of the denoising filter by considering a localized bayesian prior the localized prior leverages the similarity of the targeted database alleviates the intensive bayesian computation and links the new method to the classical linear minimum mean squared error estimation we demonstrate applications of the proposed method in a variety of scenarios including text images multiview images and face images experimental results show the superiority of the new algorithm over existing methods

on the use of the residue theorem for the efficient evaluation of band averaged input power into linear second order dynamic systems abstract an alternative to numerical quadrature is proposed to compute the power injected into a vibrating structure over a certain frequency band instead of evaluating the system response at several sampling frequencies within the considered band the integral is computed by estimating the residue at a few complex frequencies corresponding to the poles of the weighting function this technique provides considerable benefits in terms of computation time since the integration is independent of the width of the frequency band two application examples show the effectiveness of the approach firstly the use of a butterworth filter instead of a rectangular weighting function is assessed secondly the accuracy of the approximation in case of hysteretic damping is proven finally the computational performance of the technique is compared with classical numerical quadrature schemes

equivalences and the tilting theory abstract we study a natural generalization of n modules and hence also of modules by introducing the notion of modules the most important results about n modules and also modules are extended to modules for example theorem 2 7 etc an interesting subclass of the class of modules namely the class of tilting modules may be viewed as a more natural generalization of tilting modules of finite projective dimension to infinite projective dimension we show that the generalization of the brenner butler theorem in the tilting theory holds for tilting modules theorem 3 9

iterative cdma multiuser receiver with soft decision directed channel estimation we develop an iterative code division multiple access cdma receiver for multipath block fading channels in the uplink the mean square error mse of the channel estimates is reduced iteratively by using soft data estimates as additional pilots the multiuser detector performs parallel interference cancellation pic with subsequent linear filtering we consider a single user matched filter sumf and develop a low complexity linear minimum mse lmmse filter for intersymbol interference isi channels that allows for 33 more users than the sumf we investigate two choices of training sequences for initial channel estimation the first is a random pilot symbol sequence modulated by a short spreading sequence rand and the second is a perfect root of unity sequence prus used as long sounding chip sequence we observe that the rand scheme approaches the single user bound up to 2 db and in case of prus up to 1 db at a target bit error rate ber of 10 3 further several channel estimators are developed that use various combinations of soft decision symbols and statistical a priori knowledge about the channel these are the approximated least squares als approximated linear mmse almmse and linear mmse lmmse estimators the iterative estimators show an improvement of 2 5 and 5 db with prus and rand pilots respectively over estimators that do not exploit soft feedback symbols at a ber of 10 3 the als is sacrificing less than 0 6 db to obtain a ber of 10 3 in a system at load 1 5 when compared with the almmse and lmmse schemes the load is understood as the ratio of the number of users to the spreading factor this paper shows that significant improvements in system capacity can be achieved in multipath scenarios with low complexity choices of multiuser detectors and channel estimators

analytic sequential weiss weinstein bounds in this paper we explore a sequential bayesian bound for state space models focusing on hybrid continuous and discrete random states we provide an analytic recursion for the sequential weiss weinstein sww bound for linear state space models with solutions for gaussian uniform and exponential distributions as derived as well as for a combination of these we compare the sww bound for discretized states with the corresponding bound for the continuous states the sww bound is contrasted with the sequential cramer rao bound for gaussian distributions practical issues of sww bounds are discussed and numerical simulation results provide insights into their behavior

em based recursive estimation of channel parameters recursive online expectation maximization em algorithm along with stochastic approximation is employed in this paper to estimate unknown time invariant variant parameters the impulse response of a linear system channel is modeled as an unknown deterministic vector process and as a gaussian vector process with unknown stochastic characteristics using these models which are embedded in white or colored gaussian noise different types of recursive least squares rls kalman filtering and smoothing and combined rls and kalman type algorithms are derived directly from the recursive em algorithm the estimation of unknown parameters also generates new recursive algorithms for situations such as additive colored noise modeled by an autoregressive process the recursive em algorithm is shown as a powerful tool which unifies the derivations of many adaptive estimation methods

every module is finitely generated abstract we solve one of the main problems of the theory of representable equivalences of module categories we prove that every module over an arbitrary associative ring r with unit is finitely generated consequently we obtain the equality of the classes of all modules and all quasi progenerators provided that r is commutative

bounds on maximum likelihood ratio part ii application to antenna array detection estimation with imperfect wavefront coherence the multiple hypothesis testing problem of the detection estimation of an unknown number of independent gaussian point sources is adequately addressed by likelihood ratio lr maximization over the set of admissible covariance matrix models we introduce nonasymptotic lower and upper bounds for the maximum lr since lr optimization is generally a nonconvex multiextremal problem any practical solution could now be tested against these bounds enabling a high probability of recognizing nonoptimal solutions we demonstrate that in many applications the lower bound is quite tight with approximate maximum likelihood ml techniques often unable to approach this bound the introduced lower bound analysis is shown to be very efficient in determining whether or not performance breakdown has occurred for subspace based direction of arrival doa estimation techniques we also demonstrate that by proper lr maximization we can extend the range of signal to noise ratio snr values and or number of data samples wherein accurate parameter estimates are produced yet when the snr and or sample size falls below a certain limit for a given scenario we show that ml estimation suffers from a discontinuity in the parameter estimates a phenomenon that cannot be eliminated within the ml paradigm

on minimum variance unbiased estimation of clock offset in a two way message exchange mechanism for many applications distributed networks require the local clocks of the constituent nodes to run close to an agreed upon notion of time most of the widely used clock synchronization algorithms in such systems employ the sender receiver protocol based on a two way timing message exchange paradigm maximum likelihood estimator mle of the clock offset based on the timing message exchanges between two clocks was derived in d r jeske on maximum likelihood estimation of clock offset ieee trans commun vol 53 pp 53 54 jan 2005 when the fixed delays are symmetric and the variable delays in each direction assume an exponential distribution with an unknown mean herein the best linear unbiased estimate using order statistics blue os of the clock offset between two nodes is derived assuming both symmetric and asymmetric exponential network delays respectively the rao blackwell lehmann scheffe theorem is then exploited to obtain the minimum variance unbiased estimate mvue for the clock offset which it is shown to coincide with the blue os in addition it is found that the mvue of the clock offset in the presence of symmetric network delays also coincides with the mle finally in the presence of asymmetric network delays although the mle is biased it is shown to achieve lesser mean square error mse than the mvue in the region around the point where the bidirectional network link delays are symmetric and hence its merit as the most versatile estimator is fairly justified

a circular stability test for general polynomials abstract we extend a new stability test proposed recently for discrete system polynomials 1 to polynomials with complex coefficients the method is based on a three term recursion of a conjugate symmetric sequence of polynomials the complex version has the same relative improved efficiency as the real version in comparison to the classical schur cohn formulation for counting the number of zeros of a polynomial with respect to the unit circle furthermore if desirable the complex text can be carried out using only real polynomials and arithmetic

approximation formulae for the acoustic radiation impedance of a cylindrical pipe useful approximation formulae for radiation impedance are given for the reflection coefficients of both infinitely flanged and unflanged rigid walled cylindrical ducts the expressions guarantee that simple but necessary physical and mathematical principles are met like hermitian symmetry for the reflection coefficient identical behaviour of positive and negative frequencies and causality for the impulse response a non causal but more accurate expression is also proposed that is suitable for frequency domain applications the formulae are obtained by analytical and numerical fitting to reference results from levine and schwinger for the unflanged case and extracted from the radiation impedance matrix given by zorumski for the infinite flanged case

class of widely linear complex kalman filters recently a class of widely linear augmented complex valued kalman filters kfs that make use of augmented complex statistics have been proposed for sequential state space estimation of the generality of complex signals this was achieved in the context of neural network training and has allowed for a unified treatment of both second order circular and noncircular signals that is both those with rotation invariant and rotation dependent distributions in this paper we revisit the augmented complex kf augmented complex extended kf and augmented complex unscented kf in a more general context and analyze their performances for different degrees of noncircularity of input and the state and measurement noises for rigor a theoretical bound for the performance advantage of widely linear kfs over their strictly linear counterparts is provided the analysis also addresses the duality with bivariate real valued kfs together with several issues of implementation simulations using both synthetic and real world proper and improper signals support the analysis

uplink synchronization in ofdma spectrum sharing systems spectrum sharing employs dynamic allocation of frequency resources for a more efficient use of the radio spectrum despite its appealing features this technology inevitably complicates the synchronization task which must be accomplished in an environment that may involve interference this paper considers the uplink of an orthogonal frequency division multiple access ofdma based spectrum sharing system and provides solutions for estimating the frequency and timing errors of multiple unsynchronized users in doing so we exploit suitably designed training blocks and apply maximum likelihood methods after modeling the interference power on each subcarrier as a random variable with an inverse gamma distribution the resulting frequency estimator turns out to be the extension to a multiuser scenario of a scheme that has previously been proposed for single user spectrum sharing systems timing recovery is more challenging and leads to a complete search over a multidimensional domain to overcome such a difficulty two alternative approaches are proposed the first one relies on a simplifying assumption about the interference distribution in the frequency domain while the second scheme operates in an iterative fashion according to the expectation maximization algorithm

some sampling properties of common phase estimators the instantaneous phase of neural rhythms is important to many neuroscience related studies in this letter we show that the statistical sampling properties of three instantaneous phase estimators commonly employed to analyze neuroscience data share common features allowing an analytical investigation into their behavior these three phase estimators the hilbert complex morlet and discrete fourier transform are each shown to maximize the likelihood of the data assuming the observation of different neural signals this connection explored with the use of a geometric argument is used to describe the bias and variance properties of each of the phase estimators their temporal dependence and the effect of model misspecification this analysis suggests how prior knowledge about a rhythmic signal can be used to improve the accuracy of phase estimates

representation of mutual information via input estimates a relationship between information theory and estimation theory was recently shown for the gaussian channel relating the derivative of mutual information with the minimum mean square error this paper generalizes the link between information theory and estimation theory to arbitrary channels giving representations of the derivative of mutual information as a function of the conditional marginal input distributions given the outputs we illustrate the use of this representation in the efficient numerical computation of the mutual information achieved by inputs such as specific codes or natural language

the risk unbiased cramer rao bound for non bayesian multivariate parameter estimation how accurately can one estimate a deterministic parameter subject to other unknown deterministic model nuisance parameters the most popular answer to this question is given by the cramer rao bound crb the main assumption behind the derivation of the crb is local unbiased estimation of all model parameters the foundations of this paper rely on doubting this assumption generally in multivariate parameter estimation each parameter in its turn can be treated as a single parameter of interest whereas the other model parameters are treated as nuisance as their misknowledge interferes with the estimation of the parameter of interest this approach is utilized in this paper to provide a fresh look at deterministic parameter estimation a new cramer rao cr type bound is derived without assuming unbiased estimation of the nuisance parameters rather than that we apply lehmann s concept of unbiasedness for a risk that measures the distance between the estimator and the locally best unbiased estimator which assumes perfect knowledge of the nuisance parameters the proposed risk unbiased crb rucrb is proven to be asymptotically attainable by the maximum likelihood estimator while being tighter than the conventional crb furthermore simulations verify the asymptotic achievability of the rucrb by the maximum likelihood estimator for an array processing problem

distributed snr estimation with power constrained signaling over gaussian multiple access channels a sensor network is used for distributed signal to noise ratio snr estimation in a single time snapshot sensors observe a signal embedded in noise and each observation is phase modulated using a constant modulus scheme and transmitted over a gaussian multiple access channel to a fusion center at the fusion center the mean and variance are estimated jointly using an asymptotically minimum variance estimator it is shown that this joint estimator decouples into simple individual estimators of the mean and the variance the constant modulus phase modulation scheme ensures a fixed transmit power robust estimation across several sensing noise distributions as well as an snr estimate that requires a single set of transmissions from the sensors to the fusion center the estimators are evaluated in terms of asymptotic variance which are then used to evaluate the performance of the snr estimator with gaussian and cauchy sensing noise distributions in the cases of total transmit power constraint as well as a per sensor power constraint for each sensing noise distribution the optimal phase transmission parameters are also determined the asymptotic relative efficiency of the estimators is evaluated it is shown that among the noise distributions considered the estimators are asymptotically efficient only when the noise distribution is gaussian simulation results corroborate analytical results

understanding blind deconvolution algorithms blind deconvolution is the recovery of a sharp version of a blurred image when the blur kernel is unknown recent algorithms have afforded dramatic progress yet many aspects of the problem remain challenging and hard to understand the goal of this paper is to analyze and evaluate recent blind deconvolution algorithms both theoretically and experimentally we explain the previously reported failure of the naive map approach by demonstrating that it mostly favors no blur explanations we show that using reasonable image priors a naive simulations map estimation of both latent image and blur kernel is guaranteed to fail even with infinitely large images sampled from the prior on the other hand we show that since the kernel size is often smaller than the image size a map estimation of the kernel alone is well constrained and is guaranteed to succeed to recover the true blur the plethora of recent deconvolution techniques makes an experimental evaluation on ground truth data important as a first step toward this experimental evaluation we have collected blur data with ground truth and compared recent algorithms under equal settings additionally our data demonstrate that the shift invariant blur assumption made by most algorithms is often violated

improvement of tdoa position fixing using the likelihood curvature a conventional multilateration is a two step process where in the first step the time difference of arrivals tdoa of a signal at multiple sensors are estimated and in the second step these tdoas are used in some position fixing technique to estimate the location of an emitter several estimators have been proposed over the years for the estimation of the tdoas many techniques have been proposed for position fixing as well much of the research on position fixing has been focused on obtaining a simplified closed form solution for the unknown deterministic signal model stein had derived the maximum likelihood estimator mle for the tdoa between two sensors which is the peak location of the cross correlation function since the asymptotic variance of an mle approaches the cramer rao lower bound crlb which is the inverse of the negative of the expected value of the curvature of the log likelihood function using this as a motivation we propose a weighted least squares type position fixing technique where the weights are computed from the curvature of the log likelihood function

vibration source identification using corrected finite difference schemes abstract this paper addresses the problem of the location and identification of vibration excitations from the measurement of the displacement field of a vibrating structure it constitutes an improvement of the force analysis technique published several years ago the development is based on the use of the motion equation which is discretized by finite difference schemes approximating spatial derivatives of the displacement in a first instance the error due to this approximation is analytically calculated in the case of beams and the low pass filtering effect of the finite difference schemes in the wavenumber domain is shown this filter also contains singularities implying bias errors especially if the spacing between sensors is chosen in order to regularize the problem in a second instance a corrected value is applied to the classic schemes used in the force analysis technique which suppresses completely the singularities of the filter after the complete description of the corrected force analysis technique on beams the extension to plates is described where simulations with noisy data show the very good accuracy one can obtain without the requirement of an added regularization for the excitation identification

identification of mechanical properties of elastically restrained laminated composite plates using vibration data abstract a nondestructive evaluation method using vibration data to determine mechanical properties material and spring constants of elastically restrained laminated composite plates is presented the rayleigh ritz method in which a set of legendre s polynomials is adopted to approximate the plate deflection is used to determine the theoretical natural frequencies of the elastically restrained laminated composite plates a number of natural frequencies extracted from the impulse vibration test data of the laminated composite plates supported by elastic restraints at both the edges and centers of the plates are used in the present method to determine the mechanical properties of the plates the sum of the squared differences function which measures the differences between the experimentally and theoretically predicted natural frequencies of the elastically restrained laminated composite plates is established the identification of the plate mechanical properties is then formulated as a constrained minimization problem in which the mechanical properties are determined by making the sum of the squared differences function a global minimum the feasibility and accuracy of the proposed method are studied by means of several numerical examples on the mechanical properties identification of elastically restrained laminated composite plates with different layups made of various composite materials experimental investigation of the mechanical properties identification of several elastically restrained laminated composite plates has been performed to illustrate the applications of the present method it has been shown that the present method can produce good estimates of the mechanical properties of the elastically restrained laminated composite plates in an efficient and effective way

interpretation and identification of minimum phase reflection coefficients if the acoustic reflection coefficient is minimum phase then the causality condition can be used to reconstruct its phase from its magnitude such reconstructions are useful when environmental conditions obscure the phase which is vital to understanding the dynamics of the reflecting object however the reconstructions are usually impossible because one cannot be sure that the reflection coefficient is minimum phase the present work addresses this difficulty by formulating a time domain description of the minimum phase condition and by identifying classes of submerged objects that always create minimum phase reflection coefficients numerical examples are used to confirm the analytical findings and to illustrate their applicability to objects that reflect sound with a wide range of magnitudes

robust rls in the presence of correlated noise using outlier sparsity relative to batch alternatives the recursive least squares rls algorithm has well appreciated merits of reduced complexity and storage requirements for online processing of stationary signals and also for tracking slowly varying nonstationary signals however rls is challenged when in addition to noise outliers are also present in the data due to e g impulsive disturbances existing robust rls approaches are resilient to outliers but require the nominal noise to be white an assumption that may not hold in e g sensor networks where neighboring sensors are affected by correlated ambient noise prewhitening with the known noise covariance is not a viable option because it spreads the outliers to noncontaminated measurements which leads to inefficient utilization of the available data and unsatisfactory performance in this correspondence a robust rls algorithm is developed capable of handling outliers and correlated noise simultaneously in the proposed method outliers are treated as nuisance variables and estimated jointly with the wanted parameters identifiability is ensured by exploiting the sparsity of outliers which is effected via regularizing the least squares ls criterion with the l1 norm of the outlier vectors this leads to an optimization problem whose solution yields the robust rls estimates for low complexity real time operation a suboptimal online algorithm is proposed which entails closed form updates per time step in the spirit of rls simulations demonstrate the effectiveness and improved performance of the proposed method in comparison with the nonrobust rls and its state of the art robust renditions

location estimation of a random signal source based on correlated sensor observations the problem of location estimation of a source of random signals using a network of sensors is considered a novel maximum likelihood estimation mle based approach using copula functions is proposed the measurements received at the sensors are often spatially correlated and characterized by a multivariate distribution using the theory of copulas the joint parametric density of sensor observations joint likelihood is approximated assuming only the knowledge of the marginal likelihood functions of the sensor observations the problem of selecting the best copula function to model the joint likelihood is approached as one of model selection and a model fusion strategy is used to reduce the effect of selection bias an example involving source localization of a poisson source is presented to illustrate the proposed approach and demonstrate its performance

robust precoding with limited feedback design based on precoding mse for mu miso systems for the separation of the signals in the vector broadcast channel bc some information about the channel state is necessary at the transmitter in many cases this channel state information csi must be fed back from the receivers to the transmitter we jointly design the channel estimators and the quantizers at the receivers together with the precoder at the transmitter based on a precoder centric criterion i e the minimization of a mean square error mse metric appropriate for the precoder design this is in contrast to our previous works where the quantizer design was based on a csi mse metric i e based on the minimization of the mse between the true channel and the channel recovered by the transmitter using a feedback channel interestingly the estimators resulting from this joint formulation are independent of the used codebook the codebook entries are the employed precoders therefore each receiver feeds back the index of a set of precoders and the intersection of the sets gives the appropriate precoder since the quantizers of the different receivers have to work separately the metric for the computation of the partition cells cannot be expressed as a simple squared error depending on the quantizer output the proposed system based on a joint optimization clearly outperforms previous designs with separate optimization of feedback and precoding

tilting modules of finite projective dimension and a generalization of modules abstract it is well known that tilting modules of projective dimension 1 coincide with modules generating all injectives this result is extended in this paper namely we generalize modules to so called n modules and show that tilting modules of projective dimension n are n modules which n present all injectives

tilting modules of finite projective dimension tilting modules are well known and are useful in the representation theory of artinian algebras 2 4 6 11 the purpose of this paper is to define tilting modules of finite projective dimension and prove some fundamental results a unital left a module a t over a ring a is said to be a tilting module of projective dimension 0 is an integer if it satisfies the following three conditions 1 a t has a projective resolution

a characterization of the tilting pair abstract let a be an artin algebra following miyashita a pair c t in a mod is called tilting provided both c and t are selforthogonal such that t add a c and c add a t in this note we extend a simple beautiful characterization of tilting modules given by bazzoni to tilting pairs in the case of artin algebras

auditory motivated level crossing approach to instantaneous frequency estimation we address the problem of estimating the instantaneous frequency if of a phase signal using its level crossing lc information based on front end auditory processing motivation we show that the problem of if estimation using lc information can be cast in the framework of estimation from irregularly sampled data the formulation has the generality of estimating different types of if without the need for a quasistationary assumption we consider two types of if polynomial and bandlimited we use polynomial interpolating functions for the former and for the latter we propose a novel line plus sum of sines model the model parameters are estimated by linear regression considering the noisy case lc data for different levels is analyzed and methods for combining different estimators from lcs are discussed theoretical and extensive simulation results show that the performance of the zero crossing zc based if estimator and the level crossing based if estimator with smaller level values is better than those obtained with higher level values or their combinations the new technique reaches the crame spl acute r rao bound crb roughly above 4 db signal to noise ratio snr and its performance does not deteriorate rapidly with mismatch in the if order compared with the other techniques in the literature

rigid body localization using sensor networks a framework for joint position and orientation estimation of a rigid body using range measurements is proposed we consider a setup in which a few sensors are mounted on a rigid body the absolute position of the rigid body is not known however we know how the sensors are mounted on the rigid body i e the sensor topology is known the rigid body is localized using noisy range measurements between the sensors and a few anchors nodes with known absolute positions and without using any inertial measurements we propose a least squares ls and a number of constrained ls estimators where the constrained estimators solve an optimization problem on the stiefel manifold as a benchmark we derive a unitarily constrained cramer rao bound finally the known topology of the sensors can be perturbed during fabrication or if the body is not entirely rigid to take these perturbations into account constrained total least squares estimators are also proposed

multi objective parameter identification of euler bernoulli beams under axial load abstract identification of physical parameters of the partial differential equation describing transverse vibrations of an axially loaded euler bernoulli beam ebb is proposed via a multi objective optimization formulation and solved by a genetic algorithm conflicting objectives such as performance and stability are specifically formulated and optimized simultaneously stability is quantified in terms of the solution s time growth factor physical parameter sets in the resulting pareto front approximation represent best trade offs with respect to the multiple objectives to compute output error performance objectives the ebb equation is discretized via finite differences in space and time and reformulated to a state space system identifiability is verified by checking regularity of the so called fisher information matrix the identification methodology is capable of determining material parameters including damping as well as the axial load from few spatially concentrated measurements its features are demonstrated and successfully validated on specific simulation data and measurement data obtained from a laboratory testbed

subspace partitioning for target detection and identification detection of a given target or set of targets from observed data is a problem countered in many applications regardless of the algorithm selected detection performance can be severely degraded when the subspace defined by the target data set is singular or ill conditioned high correlations between target components and their linear combinations lead to false positives and misidentifications especially for subspace based detectors in this paper we propose a subspace partitioning scheme that allows for detection to be performed in a number of better conditioned subspaces instead of the original subspace the proposed technique is applied to raman spectroscopic data analysis through both simulation and experimental results we demonstrate the improvement in the overall detection performance when using the proposed subspace partitioning scheme in conjunction with several subspace detection methods that are commonly used in practice

signal detection in complex structured para normal noise in this paper we address target detection in correlated non gaussian noise we introduce a new class of multivariate complex valued distributions that allows us to specify flexible non gaussian marginals as well as correlation between the variables while preserving circular symmetry for noise belonging to this class we study the fundamental problem of signal detection under different settings and develop the needed generalized likelihood ratio tests we also consider estimation of the noise parameters and derive the maximum likelihood formulations we evaluate the merit of our approach using numerical simulations on synthetic and real data and clearly demonstrate the advantage of using both correlations and non gaussianity

low complexity lmmse based mimo ofdm channel estimation via angle domain processing in many situations multiple input multiple output with orthogonal frequency division multiplexing mimo ofdm channels tend to be spatially correlated due for example to limited scattering prior knowledge of this channel spatial correlation and the channel frequency correlation can be exploited by using the linear minimum mean square error lmmse technique however the complexity of the 2 d lmmse technique which fully utilizes both the channel spatial and frequency correlation is quite high to solve this problem this paper presents and analyzes several low complexity suboptimal approximated lmmse channel estimation techniques in the angle domain where the channel model lends itself to a physical interpretation the choice of angle domain techniques is largely dependent on the extent of channel stochastic information e g channel correlation or power that is available to the receiver nevertheless all the proposed angle domain techniques have much lower complexity compared to the 2 d lmmse technique further all the angle domain techniques improve over the conventional least square ls technique for all the typical mimo ofdm models under consideration more importantly our simulation results show that the angle domain quasi 1 d ql d lmmse technique can achieve similar performance compared to the 2 d lmmse technique for all typical mimo ofdm models with significantly lower complexity

detection of gaussian constellations in mimo systems under imperfect csi this paper considers the problem of gaussian symbols detection in mimo systems in the presence of channel estimation errors under this framework we develop a computationally efficient approximations of the map detector the new detectors are based on a relaxation of the discrete nature of the digital constellation and on the channel estimation error statistics this leads to a non convex program that is solved efficiently via a hidden convexity minimization approach additionally we show that using a bayesian em approach comparable ber performance to that of the map detector can be achieved next we extend the detection scheme to the case where the noise variance is unknown we present a modified bayesian em approach with annealed gibbs sampling to perform joint noise variance estimation and symbols detection simulation results in a random mimo system show that the proposed algorithm outperforms the linear mmse receiver in terms of ber

fundamentals of statistical signal processing estimation theory minimum variance unbiased estimation cramer rao lower bound linear models general minimum variance unbiased estimation best linear unbiased estimators maximum likelihood estimation least squares method of moments the bayesian philosophy general bayesian estimators linear bayesian estimators kalman filters summary of estimators extension for complex data and parameters

on modules with trivial self extensions throughout this note all rings will be self basic connected artin algebras over a fixed commutative local artin ring k and all modules will be finitely generated homomorphisms will be written on the opposite side of the scalars by mod a resp a mod we denote the category of all right resp left a modules for an artin algebra a the ordinary duality functor is denoted by d mod a 2 a mod i e d hom f with the minimal injective cogenerator i over k we are interested in the bimodules bta with the following properties

successive and asymptotically efficient localization of sensor nodes in closed form accurate localization of nodes in a sensor network is a crucial step before the sensor network can be utilized for various applications this paper proposes a successive estimation method to self localize the sensor nodes using time of arrival toa measurements through the aid of a few anchor nodes whose positions are known a priori the successive nature of the proposed algorithm makes it attractive for distributed computation in a resource constrained environment the proposed technique uses subsets of toas to obtain coarse sensor node estimates depending on available computation and transmission resources the node positions are refined to improve their accuracies the solution of the proposed node localization algorithm is algebraic and closed form which simplifies computation and avoids possible local convergence or divergence problems as in the traditional iterative approaches a main benefit of the proposed algorithm is that although it is closed form and performs successive estimation of the node locations it is able to reach the cramer rao lower bound crlb accuracy under white gaussian measurement noise with sufficient snr this is confirmed by the theoretical analysis and corroborated by simulations

the total variance of a periodogram based spectral estimate of a stochastic process with spectral uncertainty and its application to classifier design the variance of a spectral estimate of a stochastic process is essential to the formulation and performance of a spectral classifier the overall variance of a spectral estimate originates from two sources the within class spectral uncertainty and the variance introduced in the spectral estimation procedure in this paper we derive the total variance of a periodogram based spectral estimate under some assumptions using this result we formulate a linear spectral classifier based on fisher s separability metric the classifier is used to classify two oceanographic processes ocean convection versus internal waves

fundamental limits of linear equalizers diversity capacity and complexity linear equalizers les have been widely adopted for practical systems due to their low computational complexity however it is also well known that les provide inferior performance relative to a maximum likelihood equalizer mle or other near mles because les usually cannot collect the diversity order enabled by the transmitter and at the same time they lose mutual information more importantly unlike mle or near mles the performance of les has not been well quantified this hinders more general applications of les in wireless systems in this paper we reveal a fundamental link between a channel parameter orthogonality deficiency od of the channel matrix and the diversity and capacity of les we identify that when the od of channel matrix has an upper bound strictly less than 1 the same diversity order as that of mles is collected by les and the outage capacity loss relative to mles is also a constant over signal to noise ratio snr these results can be applied to designing a framework for hybrid equalizers furthermore by studying the statistical properties of the od and comparing the complexity of different equalizers we show that hybrid equalizers can trade off between performance and complexity by tuning the channel matrix od the theoretical analysis is corroborated by computer simulations

on posterior distributions for signals in gaussian noise with unknown covariance matrix a bayesian approach to estimate parameters of signals embedded in complex gaussian noise with unknown color is presented the study specifically focuses on a bayesian treatment of the unknown noise covariance matrix making up a nuisance parameter in such problems by integrating out uncertainties regarding the noise color an enhanced ability to estimate both the signal parameters as well as properties of the error is exploited several noninformative priors for the covariance matrix such as the reference prior the jeffreys prior and modifications to this are considered some of the priors result in analytical solutions whereas others demand numerical approximations in the linear signal model connections are made between the standard adaptive maximum likelihood aml estimate and a bayesian solution using the jeffreys prior with adjustments to the jeffreys prior correspondence to the regularized solution is also established this in turn enables a formal treatment of the regularization parameter simulations indicate that significant improvements compared to the aml estimator can be obtained by considering both the derived regularized solutions as well as the one obtained using the reference prior the simulations also indicate the possibility of enhancing the predictions of properties of the error as uncertainties in the noise color are acknowledged

on the minimum mean p th error in gaussian noise channels and its applications the problem of estimating an arbitrary random vector from its observation corrupted by additive white gaussian noise where the cost function is taken to be the minimum mean p th error mmpe is considered the classical minimum mean square error mmse is a special case of the mmpe several bounds properties and applications of the mmpe are derived and discussed the optimal mmpe estimator is found for gaussian and binary input distributions properties of the mmpe as a function of the input distribution signal to noise ratio snr and order p are derived the single crossing point property scpp which provides an upper bound on the mmse and which together with the mutual information mmse relationship is a powerful tool in deriving converse proofs in multi user information theory is extended to the mmpe moreover a complementary bound to the scpp is derived as a first application of the mmpe a bound on the conditional differential entropy in terms of the mmpe is provided which then yields a generalization of the ozarow wyner lower bound on the mutual information achieved by a discrete input on a gaussian noise channel as a second application the mmpe is shown to improve on previous characterizations of the phase transition phenomenon that manifests in the limit as the length of the capacity achieving code goes to infinity as a discontinuity of the mmse as a function of snr as a final application the mmpe is used to show new bounds on the second derivative of mutual information or the first derivative of the mmse

applications of the causality condition to one dimensional acoustic reflection problems the causality condition is examined as a means of determining frequency domain information about a submerged object from a partial knowledge of its acoustic reflection characteristics a one dimensional problem is considered in which an acoustic wave reflects from an object that is described by the impedance it presents to the fluid two new applications of the causality condition to the frequency domain analysis of this problem are investigated and illustrated by numerical examples in each application the causality condition is used to find the object s complex impedance from a knowledge of the reflected wave s magnitude the first application is to experimental studies where one desires a knowledge of an object s complex impedance but practical limitations only allow a measurement of the reflected wave amplitude analysis shows that the causality condition may be used to determine the phase of the reflected wave and hence the object s impedance if the reflection coefficient is minimum phase when this is true examples suggest that the phase of the reflection coefficient may be accurately determined from the causality condition even in the presence of noise and band limited data the second application is to design situations where one wishes to create an object that reflects sound with a specified frequency dependent magnitude the causality condition may aid the designer by providing a knowledge of all causal object impedances that produce the same reflection coefficient magnitude a numerical example is presented in which a variety of causal object impedances produce the same reflection coefficient magnitude over an infinite frequency range

estimation of flows in flow networks abstract let g be a directed graph with an unknown flow on each edge such that the following flow conservation constraint is maintained except for sources and sinks the sum of flows into a node equals the sum of flows going out of a node given a noisy measurement of the flow on each edge the problem we address which we call the m ost p robable f low e stimation problem mpfe is to estimate the most probable assignment of flow for every edge such that the flow conservation constraint is maintained we provide an algorithm called y mpfe for solving the mpfe problem when the measurement error is gaussian g aussian mpfe the algorithm works in o e v 2 when the underlying undirected graph of g is a 2 connected planar graph and in o e v when it is a 2 connected serial parallel graph or a tree this result is applicable to any m inimum c ost f low problem for which the cost function is e x e e 2 for edge e where e and e are constants and x e is the flow on edge e we show that for all topologies the g aussian mpfe s precision for each edge is analogous to the equivalent resistance measured in series to this edge in an electrical network built by replacing every edge with a resistor reflecting the measurement s precision on that edge

robust structural damage identification based on multi objective optimization structural damage identification is an inverse problem which often is formulated as an optimization problem the design variables are degrees of damage in computational model and the objective is the discrepancies between the computed responses and the measured responses conventional single objective optimization approach defines the objective function by combining multiple error terms into a single one which leads to a weaker constraint in solving the identification problem an alternative approach explained in this paper is a multi objective approach that simultaneously minimizes multiple error terms a stronger constraint from multiple objectives promotes the solutions to converge to the correct solution numerical examples based on static testing are provided to illustrate the multi objective approach also conceptual explanations are given to extend the approach to include both the static testing and the dynamic testing expected challenges will also be explained

hybrid fm polynomial phase signal modeling parameter estimation and cramer rao bounds parameter estimation for a class of nonstationary signal models is addressed the class contains combination of a polynomial phase signal pps and a frequency modulated fm component of the sinusoidal or hyperbolic type such signals appear in radar and sonar applications involving moving targets with vibrating or rotating components a novel approach is proposed that allows us to decouple estimation of the fm parameters from those of the pps relying on properties of the multilag high order ambiguity function ml haf the accuracy achievable by any unbiased estimator of the hybrid fm pps parameters is investigated by means of the cramer rao lower bounds crlbs both exact and large sample approximate expressions of the bounds are derived and compared with the performance of the proposed methods based on monte carlo simulations

antenna geometry conditions for mimo radar with uncoupled direction estimation we mainly focus on the role played by the antenna geometry in the direction estimation performance for a direction finding df bistatic multiple input multiple output mimo radar first we introduce the signal and the noise models which satisfy the space time separability conditions then we derive an expression of the cramer rao lower bound crlb on target parameters with the antenna locations for a single point target in the far field scenario we show that under the space time separability conditions the temporal dimension parameters range and range rate and spatial dimension parameters direction of departure dod and the direction of arrival doa are uncoupled we also show that dod and doa are uncoupled because of their spatial independence in addition we derive a set of the necessary and sufficient geometrical constraints for the uncoupled direction estimation which is based on the diagonal fisher information matrix fim we present that when both the transmit and the receive antenna location parameters have equivalent auto moment of inertia tensors of x and y axes and zero cross moment of inertia tensors of x y and z axes the bistatic mimo radar system with uncoupled direction estimation can be obtained the corresponding conditions are extended to monostatic mimo radar case for their commonness of the colocated antenna geometry in numerical example section we show several representative antenna geometries to illustrate the antenna geometry conditions derived in this paper

quasi ml period estimation from incomplete timing data given a noisy sequence of possibly shifted integer multiples of a certain period it is often of interest to accurately estimate the period with known integer regressors the problem is classical linear regression in many applications however the regressors are unknown integers and only loose bounds on the period are available examples include hop period and timing estimation wherein hops may be missed at the output of the frequency discriminator or the emitter may hop out of band pulse repetition interval pri analysis and passive rotating beam radio scanning we study several pertinent period estimators our emphasis is on a quasi maximum likelihood approach developed herein and an earlier method based on the fourier transform of a dirac delta train representation of the data surprisingly both are capable of attaining the clairvoyant crame spl acute r rao bound at moderate signal to noise ratios snrs even for short e g 10 samples we carefully address parameter identifiability issues and corroborate our findings with extensive simulations

new results on deterministic cramer rao bounds for real and complex parameters the cramer rao bounds crb is a lower bound of great interest for system analysis and design in the asymptotic region high signal to noise ratio snr and or large number of snapshots as it is simple to calculate and it is usually possible to obtain closed form expressions the first part of the paper is a generalization to complex parameters of the barankin rationale for deriving mse lower bounds that is the minimization of a norm under a set of linear constraints with the norm minimization approach the study of fisher information matrix fim singularity constrained crb and regularity conditions become straightforward corollaries of the derivation the second part provides new results useful for system analysis and design a general reparameterization inequality the equivalence between reparameterization and equality constraints and an explicit relationship between parameters unidentifiability and fim singularity

quasi tilting modules and counter equivalences abstract given two ringsrands we study the category equivalences t y where t is a torsion class ofr modules and y is a torsion free class ofs modules these equivalences correspond to quasi tilting triples r v s wherervsis a bimodule which has locally a tilting behavior comparing this setting with tilting bimodules and more generally with the torsion theory counter equivalences introduced by colby and fuller we prove a local version of the tilting theorem for quasi tilting triples a whole section is devoted to examples in case of algebras over a field

on the evaluation of the polyanskiy poor verdu converse bound for finite block length coding in awgn a tight converse bound to the channel coding rate in the finite block length regime and under additive white gaussian noise conditions was recently proposed by polyanskiy poor verdu ppv the bound is a generalization of a number of other classical results and it was also claimed to be equivalent to shannon s 1959 cone packing bound in this paper we investigate methods for a reliable numerical evaluation of the bound which is troublesome even for not too large values of the block length n by compactly expressing the polyanskiy poor and verdu ppv converse bound in terms of non central chi squared distributions and by evaluating those through an integral expression and a corresponding series expansion which exploit a method proposed by temme as a result a robust evaluation method and new insights on the bound s asymptotics as well as new approximate expressions are obtained

time domain responses of a prestressed beam and prestress identification abstract the time domain response of a prestressed euler bernoulli beam under external excitation is studied based on modal superposition the prestress force is then identified in the time domain by a system identification approach and tikhonov regularization technique is used to provide bounds to the ill conditioned results in the identified problem both measured displacements and strains are used the noise effect is improved using the orthogonal polynomial function and cases with either sinusoidal or impulsive excitations are illustrated to give very good results from the lower three measured modes and data obtained from three measurement points work in this paper demonstrates the feasibility of indirectly identifying the prestress force in a beam